Imported Upstream version 1.0.0.9910upstream/1.0.0.9910

34 files changed, 38 insertions, 4453 deletions

diff --git a/src/mscorlib/src/System/IO/BinaryReader.cs b/src/mscorlib/src/System/IO/BinaryReader.cs
index 4145a7f4f6..d973860472 100644
--- a/src/mscorlib/src/System/IO/BinaryReader.cs
+++ b/src/mscorlib/src/System/IO/BinaryReader.cs
@@ -23,7 +23,6 @@ namespace System.IO {
     using System.Diagnostics.Contracts;
     using System.Security;
 
-[System.Runtime.InteropServices.ComVisible(true)]
     public class BinaryReader : IDisposable
     {
         private const int MaxCharBytesSize = 128;
diff --git a/src/mscorlib/src/System/IO/BinaryWriter.cs b/src/mscorlib/src/System/IO/BinaryWriter.cs
index f99b4d3d42..b6c562534c 100644
--- a/src/mscorlib/src/System/IO/BinaryWriter.cs
+++ b/src/mscorlib/src/System/IO/BinaryWriter.cs
@@ -26,7 +26,6 @@ namespace System.IO {
     // give unique encodings.
     //
     [Serializable]
-    [System.Runtime.InteropServices.ComVisible(true)]
     public class BinaryWriter : IDisposable
     {
         public static readonly BinaryWriter Null = new BinaryWriter();
@@ -185,7 +184,7 @@ namespace System.IO {
 
             Debug.Assert(_encoding.GetMaxByteCount(1) <= 16, "_encoding.GetMaxByteCount(1) <= 16)");
             int numBytes = 0;
-            fixed(byte * pBytes = _buffer) {
+            fixed(byte * pBytes = &_buffer[0]) {
                 numBytes = _encoder.GetBytes(&ch, 1, pBytes, _buffer.Length, flush: true);
             }
             OutStream.Write(_buffer, 0, numBytes);
@@ -382,7 +381,7 @@ namespace System.IO {
                         }
                         fixed (char* pChars = value)
                         {
-                            fixed (byte* pBytes = _largeByteBuffer)
+                            fixed (byte* pBytes = &_largeByteBuffer[0])
                             {
                                 byteLen = _encoder.GetBytes(pChars + charStart, charCount, pBytes, _largeByteBuffer.Length, charCount == numLeft);
                             }
diff --git a/src/mscorlib/src/System/IO/Directory.cs b/src/mscorlib/src/System/IO/Directory.cs
index d6b68222cd..88a669a971 100644
--- a/src/mscorlib/src/System/IO/Directory.cs
+++ b/src/mscorlib/src/System/IO/Directory.cs
@@ -17,7 +17,6 @@
 
 using System.Collections.Generic;
 using System.Security;
-using System.Security.Permissions;
 using Microsoft.Win32;
 using Microsoft.Win32.SafeHandles;
 using System.Runtime.InteropServices;
@@ -26,404 +25,7 @@ using System.Diagnostics.Contracts;
 
 namespace System.IO
 {
-    [ComVisible(true)]
-    public static class Directory {
-        public static DirectoryInfo GetParent(String path)
-        {
-            if (path==null)
-                throw new ArgumentNullException(nameof(path));
-
-            if (path.Length==0)
-                throw new ArgumentException(Environment.GetResourceString("Argument_PathEmpty"), nameof(path));
-            Contract.EndContractBlock();
-
-            string fullPath = Path.GetFullPath(path);
-
-            string s = Path.GetDirectoryName(fullPath);
-            if (s==null)
-                 return null;
-            return new DirectoryInfo(s);
-        }
-
-        public static DirectoryInfo CreateDirectory(String path) {
-            if (path == null)
-                throw new ArgumentNullException(nameof(path));
-            if (path.Length == 0)
-                throw new ArgumentException(Environment.GetResourceString("Argument_PathEmpty"));
-            Contract.EndContractBlock();
-
-            return InternalCreateDirectoryHelper(path);
-        }
-
-        internal static DirectoryInfo InternalCreateDirectoryHelper(String path)
-        {
-            Contract.Requires(path != null);
-            Contract.Requires(path.Length != 0);
-
-            String fullPath = Path.GetFullPath(path);
-
-            InternalCreateDirectory(fullPath, path, null);
-
-            return new DirectoryInfo(fullPath, false);
-        }
-
-        internal unsafe static void InternalCreateDirectory(String fullPath, String path, Object dirSecurityObj)
-        {
-            int length = fullPath.Length;
-
-            // We need to trim the trailing slash or the code will try to create 2 directories of the same name.
-            if (length >= 2 && PathInternal.IsDirectorySeparator(fullPath[length - 1]))
-                length--;
-            
-            int lengthRoot = PathInternal.GetRootLength(fullPath);
-
-            // For UNC paths that are only // or /// 
-            if (length == 2 && PathInternal.IsDirectorySeparator(fullPath[1]))
-                throw new IOException(Environment.GetResourceString("IO.IO_CannotCreateDirectory", path));
-
-            // We can save a bunch of work if the directory we want to create already exists.  This also
-            // saves us in the case where sub paths are inaccessible (due to ERROR_ACCESS_DENIED) but the
-            // final path is accessable and the directory already exists.  For example, consider trying
-            // to create c:\Foo\Bar\Baz, where everything already exists but ACLS prevent access to c:\Foo
-            // and c:\Foo\Bar.  In that case, this code will think it needs to create c:\Foo, and c:\Foo\Bar
-            // and fail to due so, causing an exception to be thrown.  This is not what we want.
-            if (InternalExists(fullPath)) {
-                return;
-            }
-
-            List<string> stackDir = new List<string>();
-
-            // Attempt to figure out which directories don't exist, and only
-            // create the ones we need.  Note that InternalExists may fail due
-            // to Win32 ACL's preventing us from seeing a directory, and this
-            // isn't threadsafe.
-
-            bool somepathexists = false;
-
-            if (length > lengthRoot) { // Special case root (fullpath = X:\\)
-                int i = length-1;
-                while (i >= lengthRoot && !somepathexists) {
-                    String dir = fullPath.Substring(0, i+1);
-                        
-                    if (!InternalExists(dir)) // Create only the ones missing
-                        stackDir.Add(dir);
-                    else
-                        somepathexists = true;
-                    
-                    while (i > lengthRoot && fullPath[i] != Path.DirectorySeparatorChar && fullPath[i] != Path.AltDirectorySeparatorChar) i--;
-                    i--;
-                }
-            }
-
-            int count = stackDir.Count;
-
-            // If we were passed a DirectorySecurity, convert it to a security
-            // descriptor and set it in he call to CreateDirectory.
-            Win32Native.SECURITY_ATTRIBUTES secAttrs = null;
-
-            bool r = true;
-            int firstError = 0;
-            String errorString = path;
-            // If all the security checks succeeded create all the directories
-            while (stackDir.Count > 0) {
-                String name = stackDir[stackDir.Count - 1];
-                stackDir.RemoveAt(stackDir.Count - 1);
-                if (PathInternal.IsDirectoryTooLong(name))
-                    throw new PathTooLongException(Environment.GetResourceString("IO.PathTooLong"));
-                r = Win32Native.CreateDirectory(name, secAttrs);
-                if (!r && (firstError == 0)) {
-                    int currentError = Marshal.GetLastWin32Error();
-                    // While we tried to avoid creating directories that don't
-                    // exist above, there are at least two cases that will 
-                    // cause us to see ERROR_ALREADY_EXISTS here.  InternalExists 
-                    // can fail because we didn't have permission to the 
-                    // directory.  Secondly, another thread or process could
-                    // create the directory between the time we check and the
-                    // time we try using the directory.  Thirdly, it could
-                    // fail because the target does exist, but is a file.
-                    if (currentError != Win32Native.ERROR_ALREADY_EXISTS)
-                        firstError = currentError;
-                    else {
-                        // If there's a file in this directory's place, or if we have ERROR_ACCESS_DENIED when checking if the directory already exists throw.
-                        if (File.InternalExists(name) || (!InternalExists(name, out currentError) && currentError == Win32Native.ERROR_ACCESS_DENIED))
-                        {
-                            firstError = currentError;
-                            errorString = name;
-                        }
-                    }
-                }
-            }
-
-            // We need this check to mask OS differences
-            // Handle CreateDirectory("X:\\foo") when X: doesn't exist. Similarly for n/w paths.
-            if ((count == 0) && !somepathexists) {
-                String root = InternalGetDirectoryRoot(fullPath);
-                if (!InternalExists(root)) {
-                    // Extract the root from the passed in path again for security.
-                    __Error.WinIOError(Win32Native.ERROR_PATH_NOT_FOUND, InternalGetDirectoryRoot(path));
-                }
-                return;
-            }
-
-            // Only throw an exception if creating the exact directory we 
-            // wanted failed to work correctly.
-            if (!r && (firstError != 0)) {
-                __Error.WinIOError(firstError, errorString);
-            }
-        }
-      
-       
-        // Tests if the given path refers to an existing DirectoryInfo on disk.
-        // 
-        // Your application must have Read permission to the directory's
-        // contents.
-        //
-        public static bool Exists(String path)
-        {
-            return InternalExistsHelper(path);
-        }
-
-        internal static bool InternalExistsHelper(String path) {
-            try
-            {
-                if (path == null)
-                    return false;
-                if (path.Length == 0)
-                    return false;
-
-                return InternalExists(Path.GetFullPath(path));
-            }
-            catch (ArgumentException) { }
-            catch (NotSupportedException) { }  // Security can throw this on ":"
-            catch (SecurityException) { }
-            catch (IOException) { }
-            catch (UnauthorizedAccessException)
-            {
-                Debug.Assert(false, "Ignore this assert and send a repro to Microsoft. This assert was tracking purposes only.");
-            }
-            return false;
-        }
-
-        // Determine whether path describes an existing directory
-        // on disk, avoiding security checks.
-        internal static bool InternalExists(String path) {
-            int lastError = Win32Native.ERROR_SUCCESS;
-            return InternalExists(path, out lastError);
-        }
-
-        // Determine whether path describes an existing directory
-        // on disk, avoiding security checks.
-        internal static bool InternalExists(String path, out int lastError) {
-            Win32Native.WIN32_FILE_ATTRIBUTE_DATA data = new Win32Native.WIN32_FILE_ATTRIBUTE_DATA();
-            lastError = File.FillAttributeInfo(path, ref data, false, true);
-
-            return (lastError == 0) && (data.fileAttributes != -1)
-                    && ((data.fileAttributes & Win32Native.FILE_ATTRIBUTE_DIRECTORY) != 0);
-        }
-
-        public static DateTime GetCreationTime(String path)
-        {
-            return File.GetCreationTime(path);
-        }
-
-        public static DateTime GetCreationTimeUtc(String path)
-        {
-            return File.GetCreationTimeUtc(path);
-        }
-
-        public static DateTime GetLastWriteTime(String path)
-        {
-            return File.GetLastWriteTime(path);
-        }
-
-        public static DateTime GetLastWriteTimeUtc(String path)
-        {
-            return File.GetLastWriteTimeUtc(path);
-        }
-
-        public static DateTime GetLastAccessTime(String path)
-        {
-            return File.GetLastAccessTime(path);
-        }
-
-        public static DateTime GetLastAccessTimeUtc(String path)
-        {
-            return File.GetLastAccessTimeUtc(path);
-        }
-
-        // Returns an array of filenames in the DirectoryInfo specified by path
-        public static String[] GetFiles(String path)
-        {
-            if (path == null)
-                throw new ArgumentNullException(nameof(path));
-            Contract.Ensures(Contract.Result<String[]>() != null);
-            Contract.EndContractBlock();
-
-            return InternalGetFiles(path, "*", SearchOption.TopDirectoryOnly);
-        }
-
-        // Returns an array of Files in the current DirectoryInfo matching the 
-        // given search pattern (ie, "*.txt").
-        public static String[] GetFiles(String path, String searchPattern)
-        {
-            if (path == null)
-                throw new ArgumentNullException(nameof(path));
-            if (searchPattern == null)
-                throw new ArgumentNullException(nameof(searchPattern));
-            Contract.Ensures(Contract.Result<String[]>() != null);
-            Contract.EndContractBlock();
-
-            return InternalGetFiles(path, searchPattern, SearchOption.TopDirectoryOnly);
-        }
-
-        // Returns an array of Files in the current DirectoryInfo matching the 
-        // given search pattern (ie, "*.txt") and search option
-        public static String[] GetFiles(String path, String searchPattern, SearchOption searchOption)
-        {
-            if (path == null)
-                throw new ArgumentNullException(nameof(path));
-            if (searchPattern == null)
-                throw new ArgumentNullException(nameof(searchPattern));
-            if ((searchOption != SearchOption.TopDirectoryOnly) && (searchOption != SearchOption.AllDirectories))
-                throw new ArgumentOutOfRangeException(nameof(searchOption), Environment.GetResourceString("ArgumentOutOfRange_Enum"));
-            Contract.Ensures(Contract.Result<String[]>() != null);
-            Contract.EndContractBlock();
-            
-            return InternalGetFiles(path, searchPattern, searchOption);
-        }
-
-        // Returns an array of Files in the current DirectoryInfo matching the 
-        // given search pattern (ie, "*.txt") and search option
-        private static String[] InternalGetFiles(String path, String searchPattern, SearchOption searchOption)
-        {
-            Contract.Requires(path != null);
-            Contract.Requires(searchPattern != null);
-            Contract.Requires(searchOption == SearchOption.AllDirectories || searchOption == SearchOption.TopDirectoryOnly);
-
-            return InternalGetFileDirectoryNames(path, path, searchPattern, true, false, searchOption, true);
-        }
-
-        internal static String[] UnsafeGetFiles(String path, String searchPattern, SearchOption searchOption)
-        {
-            Contract.Requires(path != null);
-            Contract.Requires(searchPattern != null);
-            Contract.Requires(searchOption == SearchOption.AllDirectories || searchOption == SearchOption.TopDirectoryOnly);
-
-            return InternalGetFileDirectoryNames(path, path, searchPattern, true, false, searchOption, false);
-        }
-
-        // Returns an array of Directories in the current directory.
-        public static String[] GetDirectories(String path)
-        {
-            if (path == null)
-                throw new ArgumentNullException(nameof(path));
-            Contract.Ensures(Contract.Result<String[]>() != null);
-            Contract.EndContractBlock();
-
-            return InternalGetDirectories(path, "*", SearchOption.TopDirectoryOnly);
-        }
-
-        // Returns an array of Directories in the current DirectoryInfo matching the 
-        // given search criteria (ie, "*.txt").
-        public static String[] GetDirectories(String path, String searchPattern)
-        {
-            if (path == null)
-                throw new ArgumentNullException(nameof(path));
-            if (searchPattern == null)
-                throw new ArgumentNullException(nameof(searchPattern));
-            Contract.Ensures(Contract.Result<String[]>() != null);
-            Contract.EndContractBlock();
-
-            return InternalGetDirectories(path, searchPattern, SearchOption.TopDirectoryOnly);
-        }
-
-        // Returns an array of Directories in the current DirectoryInfo matching the 
-        // given search criteria (ie, "*.txt").
-        public static String[] GetDirectories(String path, String searchPattern, SearchOption searchOption)
-        {
-            if (path == null)
-                throw new ArgumentNullException(nameof(path));
-            if (searchPattern == null)
-                throw new ArgumentNullException(nameof(searchPattern));
-            if ((searchOption != SearchOption.TopDirectoryOnly) && (searchOption != SearchOption.AllDirectories))
-                throw new ArgumentOutOfRangeException(nameof(searchOption), Environment.GetResourceString("ArgumentOutOfRange_Enum"));
-            Contract.Ensures(Contract.Result<String[]>() != null);
-            Contract.EndContractBlock();
-
-            return InternalGetDirectories(path, searchPattern, searchOption);
-        }
-
-        // Returns an array of Directories in the current DirectoryInfo matching the 
-        // given search criteria (ie, "*.txt").
-        private static String[] InternalGetDirectories(String path, String searchPattern, SearchOption searchOption)
-        {
-            Contract.Requires(path != null);
-            Contract.Requires(searchPattern != null);
-            Contract.Requires(searchOption == SearchOption.AllDirectories || searchOption == SearchOption.TopDirectoryOnly);
-            Contract.Ensures(Contract.Result<String[]>() != null);
-
-            return InternalGetFileDirectoryNames(path, path, searchPattern, false, true, searchOption, true);
-        }
-
-        internal static String[] UnsafeGetDirectories(String path, String searchPattern, SearchOption searchOption)
-        {
-            Contract.Requires(path != null);
-            Contract.Requires(searchPattern != null);
-            Contract.Requires(searchOption == SearchOption.AllDirectories || searchOption == SearchOption.TopDirectoryOnly);
-            Contract.Ensures(Contract.Result<String[]>() != null);
-
-            return InternalGetFileDirectoryNames(path, path, searchPattern, false, true, searchOption, false);
-        }
-            
-        // Returns an array of strongly typed FileSystemInfo entries in the path
-        public static String[] GetFileSystemEntries(String path)
-        {
-            if (path == null)
-                throw new ArgumentNullException(nameof(path));
-            Contract.Ensures(Contract.Result<String[]>() != null);
-            Contract.EndContractBlock();
-
-            return InternalGetFileSystemEntries(path, "*", SearchOption.TopDirectoryOnly);
-        }
-
-        // Returns an array of strongly typed FileSystemInfo entries in the path with the
-        // given search criteria (ie, "*.txt"). We disallow .. as a part of the search criteria
-        public static String[] GetFileSystemEntries(String path, String searchPattern)
-        {
-            if (path == null)
-                throw new ArgumentNullException(nameof(path));
-            if (searchPattern == null)
-                throw new ArgumentNullException(nameof(searchPattern));
-            Contract.Ensures(Contract.Result<String[]>() != null);
-            Contract.EndContractBlock();
-
-            return InternalGetFileSystemEntries(path, searchPattern, SearchOption.TopDirectoryOnly);
-        }
-
-        // Returns an array of strongly typed FileSystemInfo entries in the path with the
-        // given search criteria (ie, "*.txt"). We disallow .. as a part of the search criteria
-        public static String[] GetFileSystemEntries(String path, String searchPattern, SearchOption searchOption)
-        {
-            if (path == null)
-                throw new ArgumentNullException(nameof(path));
-            if (searchPattern == null)
-                throw new ArgumentNullException(nameof(searchPattern));
-            if ((searchOption != SearchOption.TopDirectoryOnly) && (searchOption != SearchOption.AllDirectories))
-                throw new ArgumentOutOfRangeException(nameof(searchOption), Environment.GetResourceString("ArgumentOutOfRange_Enum"));
-            Contract.Ensures(Contract.Result<String[]>() != null);
-            Contract.EndContractBlock();
-
-            return InternalGetFileSystemEntries(path, searchPattern, searchOption);
-        }
-
-        private static String[] InternalGetFileSystemEntries(String path, String searchPattern, SearchOption searchOption)
-        {
-            Contract.Requires(path != null);
-            Contract.Requires(searchPattern != null);
-            Contract.Requires(searchOption == SearchOption.AllDirectories || searchOption == SearchOption.TopDirectoryOnly);
-
-            return InternalGetFileDirectoryNames(path, path, searchPattern, true, true, searchOption, true);
-        }
+    internal static class Directory {
 
         // Private class that holds search data that is passed around 
         // in the heap based stack recursion
@@ -445,90 +47,7 @@ namespace System.IO
             public readonly SearchOption searchOption;
         }
 
-
-        // Returns fully qualified user path of dirs/files that matches the search parameters. 
-        // For recursive search this method will search through all the sub dirs  and execute 
-        // the given search criteria against every dir.
-        // For all the dirs/files returned, it will then demand path discovery permission for 
-        // their parent folders (it will avoid duplicate permission checks)
-        internal static String[] InternalGetFileDirectoryNames(String path, String userPathOriginal, String searchPattern, bool includeFiles, bool includeDirs, SearchOption searchOption, bool checkHost)
-        {
-            Contract.Requires(path != null);
-            Contract.Requires(userPathOriginal != null);
-            Contract.Requires(searchPattern != null);
-            Contract.Requires(searchOption == SearchOption.AllDirectories || searchOption == SearchOption.TopDirectoryOnly);
-
-            IEnumerable<String> enble = FileSystemEnumerableFactory.CreateFileNameIterator(
-                                                                                path, userPathOriginal, searchPattern,
-                                                                                includeFiles, includeDirs, searchOption, checkHost);
-            List<String> fileList = new List<String>(enble);
-            return fileList.ToArray();
-        }
-
-        public static IEnumerable<String> EnumerateDirectories(String path)
-        {
-            if (path == null)
-                throw new ArgumentNullException(nameof(path));
-            Contract.EndContractBlock();
-
-            return InternalEnumerateDirectories(path, "*", SearchOption.TopDirectoryOnly);
-        }
-
-        public static IEnumerable<String> EnumerateDirectories(String path, String searchPattern)
-        {
-            if (path == null)
-                throw new ArgumentNullException(nameof(path));
-            if (searchPattern == null)
-                throw new ArgumentNullException(nameof(searchPattern));
-            Contract.EndContractBlock();
-
-            return InternalEnumerateDirectories(path, searchPattern, SearchOption.TopDirectoryOnly);
-        }
-
-        public static IEnumerable<String> EnumerateDirectories(String path, String searchPattern, SearchOption searchOption)
-        {
-            if (path == null)
-                throw new ArgumentNullException(nameof(path));
-            if (searchPattern == null)
-                throw new ArgumentNullException(nameof(searchPattern));
-            if ((searchOption != SearchOption.TopDirectoryOnly) && (searchOption != SearchOption.AllDirectories))
-                throw new ArgumentOutOfRangeException(nameof(searchOption), Environment.GetResourceString("ArgumentOutOfRange_Enum"));
-            Contract.EndContractBlock();
-
-            return InternalEnumerateDirectories(path, searchPattern, searchOption);
-        }
-
-        private static IEnumerable<String> InternalEnumerateDirectories(String path, String searchPattern, SearchOption searchOption)
-        {
-            Contract.Requires(path != null);
-            Contract.Requires(searchPattern != null);
-            Contract.Requires(searchOption == SearchOption.AllDirectories || searchOption == SearchOption.TopDirectoryOnly);
-
-            return EnumerateFileSystemNames(path, searchPattern, searchOption, false, true);
-        }
-
-        public static IEnumerable<String> EnumerateFiles(String path)
-        {
-            if (path == null)
-                throw new ArgumentNullException(nameof(path));
-            Contract.Ensures(Contract.Result<IEnumerable<String>>() != null);
-            Contract.EndContractBlock();
-
-            return InternalEnumerateFiles(path, "*", SearchOption.TopDirectoryOnly);
-        }
-
-        public static IEnumerable<String> EnumerateFiles(String path, String searchPattern)
-        {
-            if (path == null)
-                throw new ArgumentNullException(nameof(path));
-            if (searchPattern == null)
-                throw new ArgumentNullException(nameof(searchPattern));
-            Contract.Ensures(Contract.Result<IEnumerable<String>>() != null);
-            Contract.EndContractBlock();
-
-            return InternalEnumerateFiles(path, searchPattern, SearchOption.TopDirectoryOnly);
-        }
-
+#if PLATFORM_UNIX
         public static IEnumerable<String> EnumerateFiles(String path, String searchPattern, SearchOption searchOption)
         {
             if (path == null)
@@ -553,52 +72,6 @@ namespace System.IO
             return EnumerateFileSystemNames(path, searchPattern, searchOption, true, false);
         }
 
-        public static IEnumerable<String> EnumerateFileSystemEntries(String path)
-        {
-            if (path == null)
-                throw new ArgumentNullException(nameof(path));
-            Contract.Ensures(Contract.Result<IEnumerable<String>>() != null);
-            Contract.EndContractBlock();
-
-            return InternalEnumerateFileSystemEntries(path, "*", SearchOption.TopDirectoryOnly);
-        }
-
-        public static IEnumerable<String> EnumerateFileSystemEntries(String path, String searchPattern)
-        {
-            if (path == null)
-                throw new ArgumentNullException(nameof(path));
-            if (searchPattern == null)
-                throw new ArgumentNullException(nameof(searchPattern));
-            Contract.Ensures(Contract.Result<IEnumerable<String>>() != null);
-            Contract.EndContractBlock();
-
-            return InternalEnumerateFileSystemEntries(path, searchPattern, SearchOption.TopDirectoryOnly);
-        }
-
-        public static IEnumerable<String> EnumerateFileSystemEntries(String path, String searchPattern, SearchOption searchOption)
-        {
-            if (path == null)
-                throw new ArgumentNullException(nameof(path));
-            if (searchPattern == null)
-                throw new ArgumentNullException(nameof(searchPattern));
-            if ((searchOption != SearchOption.TopDirectoryOnly) && (searchOption != SearchOption.AllDirectories))
-                throw new ArgumentOutOfRangeException(nameof(searchOption), Environment.GetResourceString("ArgumentOutOfRange_Enum"));
-            Contract.Ensures(Contract.Result<IEnumerable<String>>() != null);
-            Contract.EndContractBlock();
-
-            return InternalEnumerateFileSystemEntries(path, searchPattern, searchOption);
-        }
-
-        private static IEnumerable<String> InternalEnumerateFileSystemEntries(String path, String searchPattern, SearchOption searchOption)
-        {
-            Contract.Requires(path != null);
-            Contract.Requires(searchPattern != null);
-            Contract.Requires(searchOption == SearchOption.AllDirectories || searchOption == SearchOption.TopDirectoryOnly);
-            Contract.Ensures(Contract.Result<IEnumerable<String>>() != null);
-
-            return EnumerateFileSystemNames(path, searchPattern, searchOption, true, true);
-        }
-
         private static IEnumerable<String> EnumerateFileSystemNames(String path, String searchPattern, SearchOption searchOption,
                                                             bool includeFiles, bool includeDirs)
         {
@@ -610,60 +83,14 @@ namespace System.IO
             return FileSystemEnumerableFactory.CreateFileNameIterator(path, path, searchPattern,
                                                                         includeFiles, includeDirs, searchOption, true);
         }
-
-        // Retrieves the names of the logical drives on this machine in the 
-        // form "C:\". 
-        // 
-        // Your application must have System Info permission.
-        // 
-        public static String[] GetLogicalDrives()
-        {
-            Contract.Ensures(Contract.Result<String[]>() != null);
-
-#pragma warning disable 618
-            new SecurityPermission(SecurityPermissionFlag.UnmanagedCode).Demand();
-#pragma warning restore 618
-                                 
-            int drives = Win32Native.GetLogicalDrives();
-            if (drives==0)
-                __Error.WinIOError();
-            uint d = (uint)drives;
-            int count = 0;
-            while (d != 0) {
-                if (((int)d & 1) != 0) count++;
-                d >>= 1;
-            }
-            String[] result = new String[count];
-            char[] root = new char[] {'A', ':', '\\'};
-            d = (uint)drives;
-            count = 0;
-            while (d != 0) {
-                if (((int)d & 1) != 0) {
-                    result[count++] = new String(root);
-                }
-                d >>= 1;
-                root[0]++;
-            }
-            return result;
-        }
-
-        public static String GetDirectoryRoot(String path) {
-            if (path==null)
-                throw new ArgumentNullException(nameof(path));
-            Contract.EndContractBlock();
-
-            string fullPath = Path.GetFullPath(path);
-            string root = fullPath.Substring(0, PathInternal.GetRootLength(fullPath));
-
-            return root;
-        }
+#endif // PLATFORM_UNIX        
 
         internal static String InternalGetDirectoryRoot(String path) {
               if (path == null) return null;
             return path.Substring(0, PathInternal.GetRootLength(path));
         }
 
-         /*===============================CurrentDirectory===============================
+        /*===============================CurrentDirectory===============================
         **Action:  Provides a getter and setter for the current directory.  The original
         **         current DirectoryInfo is the one from which the process was started.  
         **Returns: The current DirectoryInfo (from the getter).  Void from the setter.
@@ -673,20 +100,21 @@ namespace System.IO
         public static String GetCurrentDirectory()
         {
             // Start with a buffer the size of MAX_PATH
-            using (StringBuffer buffer = new StringBuffer(260))
+            StringBuffer buffer = new StringBuffer(260);
+            try
             {
                 uint result = 0;
-                while ((result = Win32Native.GetCurrentDirectoryW(buffer.CharCapacity, buffer.GetHandle())) > buffer.CharCapacity)
+                while ((result = Win32Native.GetCurrentDirectoryW((uint)buffer.Capacity, buffer.UnderlyingArray)) > buffer.Capacity)
                 {
                     // Reported size is greater than the buffer size. Increase the capacity.
                     // The size returned includes the null only if more space is needed (this case).
-                    buffer.EnsureCharCapacity(result);
+                    buffer.EnsureCapacity(checked((int)result));
                 }
 
                 if (result == 0)
                     __Error.WinIOError();
 
-                buffer.Length = result;
+                buffer.Length = (int)result;
 
 #if !PLATFORM_UNIX
                 if (buffer.Contains('~'))
@@ -695,12 +123,16 @@ namespace System.IO
 
                 return buffer.ToString();
             }
+            finally
+            {
+                buffer.Free();
+            }
         }
 
         public static void SetCurrentDirectory(String path)
         {
             if (path==null)
-                throw new ArgumentNullException("value");
+                throw new ArgumentNullException(nameof(path));
             if (path.Length==0)
                 throw new ArgumentException(Environment.GetResourceString("Argument_PathEmpty"));
             if (path.Length >= Path.MaxPath)
@@ -718,216 +150,6 @@ namespace System.IO
                 __Error.WinIOError(errorCode, fulldestDirName);
             }
         }
-
-        public static void Move(String sourceDirName,String destDirName)
-        {
-            if (sourceDirName==null)
-                throw new ArgumentNullException(nameof(sourceDirName));
-            if (sourceDirName.Length==0)
-                throw new ArgumentException(Environment.GetResourceString("Argument_EmptyFileName"), nameof(sourceDirName));
-            if (destDirName==null)
-                throw new ArgumentNullException(nameof(destDirName));
-            if (destDirName.Length==0)
-                throw new ArgumentException(Environment.GetResourceString("Argument_EmptyFileName"), nameof(destDirName));
-
-            String sourcePath = Path.GetFullPath(sourceDirName);
-            String destPath = Path.GetFullPath(destDirName);
-
-            if (String.Compare(sourcePath, destPath, StringComparison.OrdinalIgnoreCase) == 0)
-                throw new IOException(Environment.GetResourceString("IO.IO_SourceDestMustBeDifferent"));
-
-            String sourceRoot = Path.GetPathRoot(sourcePath);
-            String destinationRoot = Path.GetPathRoot(destPath);
-            if (String.Compare(sourceRoot, destinationRoot, StringComparison.OrdinalIgnoreCase) != 0)
-                throw new IOException(Environment.GetResourceString("IO.IO_SourceDestMustHaveSameRoot"));
-    
-            if (!Win32Native.MoveFile(sourceDirName, destDirName))
-            {
-                int hr = Marshal.GetLastWin32Error();
-                if (hr == Win32Native.ERROR_FILE_NOT_FOUND) // Source dir not found
-                {
-                    hr = Win32Native.ERROR_PATH_NOT_FOUND;
-                    __Error.WinIOError(hr, sourcePath);
-                }
-                // This check was originally put in for Win9x (unfortunately without special casing it to be for Win9x only). We can't change the NT codepath now for backcomp reasons.
-                if (hr == Win32Native.ERROR_ACCESS_DENIED) // WinNT throws IOException. This check is for Win9x. We can't change it for backcomp.
-                    throw new IOException(Environment.GetResourceString("UnauthorizedAccess_IODenied_Path", sourceDirName), Win32Native.MakeHRFromErrorCode(hr));
-                __Error.WinIOError(hr, String.Empty);
-            }
-        }
-
-        public static void Delete(String path)
-        {
-            String fullPath = Path.GetFullPath(path);
-            Delete(fullPath, path, false);
-        }
-
-        public static void Delete(String path, bool recursive)
-        {
-            String fullPath = Path.GetFullPath(path);
-            Delete(fullPath, path, recursive);
-        }
-
-         // Called from DirectoryInfo as well.  FullPath is fully qualified,
-        // while the user path is used for feedback in exceptions.
-        internal static void Delete(String fullPath, String userPath, bool recursive)
-        {
-            // Do not recursively delete through reparse points.  Perhaps in a 
-            // future version we will add a new flag to control this behavior, 
-            // but for now we're much safer if we err on the conservative side.
-            // This applies to symbolic links and mount points.
-            Win32Native.WIN32_FILE_ATTRIBUTE_DATA data = new Win32Native.WIN32_FILE_ATTRIBUTE_DATA();
-            int dataInitialised = File.FillAttributeInfo(fullPath, ref data, false, true);
-            if (dataInitialised != 0) {
-                // Ensure we throw a DirectoryNotFoundException.
-                if (dataInitialised == Win32Native.ERROR_FILE_NOT_FOUND)
-                    dataInitialised = Win32Native.ERROR_PATH_NOT_FOUND;
-                __Error.WinIOError(dataInitialised, fullPath);
-            }
-
-            if (((FileAttributes)data.fileAttributes & FileAttributes.ReparsePoint) != 0)
-                recursive = false;
-
-            DeleteHelper(fullPath, userPath, recursive, true);
-        }
-
-        // Note that fullPath is fully qualified, while userPath may be relative.
-        private static void DeleteHelper(String fullPath, String userPath, bool recursive, bool throwOnTopLevelDirectoryNotFound)
-        {
-            bool r;
-            int hr;
-            Exception ex = null;
-
-            // Do not recursively delete through reparse points.  Perhaps in a 
-            // future version we will add a new flag to control this behavior, 
-            // but for now we're much safer if we err on the conservative side.
-            // This applies to symbolic links and mount points.
-            // Note the logic to check whether fullPath is a reparse point is
-            // in Delete(String, String, bool), and will set "recursive" to false.
-            // Note that Win32's DeleteFile and RemoveDirectory will just delete
-            // the reparse point itself.
-
-            if (recursive) {
-                Win32Native.WIN32_FIND_DATA data = new Win32Native.WIN32_FIND_DATA();
-                
-                // Open a Find handle
-                using (SafeFindHandle hnd = Win32Native.FindFirstFile(fullPath + Path.DirectorySeparatorChar + "*", data)) {
-                    if (hnd.IsInvalid) {
-                        hr = Marshal.GetLastWin32Error();
-                        __Error.WinIOError(hr, fullPath);
-                    }
-
-                    do {
-                        bool isDir = (0!=(data.dwFileAttributes & Win32Native.FILE_ATTRIBUTE_DIRECTORY));
-                        if (isDir) {
-                            // Skip ".", "..".
-                            if (data.cFileName.Equals(".") || data.cFileName.Equals(".."))
-                                continue;
-
-                            // Recurse for all directories, unless they are 
-                            // reparse points.  Do not follow mount points nor
-                            // symbolic links, but do delete the reparse point 
-                            // itself.
-                            bool shouldRecurse = (0 == (data.dwFileAttributes & (int) FileAttributes.ReparsePoint));
-                            if (shouldRecurse) {
-                                String newFullPath = Path.Combine(fullPath, data.cFileName);
-                                String newUserPath = Path.Combine(userPath, data.cFileName);
-                                try {
-                                    DeleteHelper(newFullPath, newUserPath, recursive, false);
-                                }
-                                catch(Exception e) {
-                                    if (ex == null) {
-                                        ex = e;
-                                    }
-                                }
-                            }
-                            else {
-                                // Check to see if this is a mount point, and
-                                // unmount it.
-                                if (data.dwReserved0 == Win32Native.IO_REPARSE_TAG_MOUNT_POINT) {
-                                    // Use full path plus a trailing '\'
-                                    String mountPoint = Path.Combine(fullPath, data.cFileName + Path.DirectorySeparatorChar);
-                                    r = Win32Native.DeleteVolumeMountPoint(mountPoint);
-                                    if (!r) {
-                                        hr = Marshal.GetLastWin32Error();
-                                        if (hr != Win32Native.ERROR_PATH_NOT_FOUND) {
-                                            try {
-                                                __Error.WinIOError(hr, data.cFileName);
-                                            }
-                                            catch(Exception e) {
-                                                if (ex == null) {
-                                                    ex = e;
-                                                }
-                                            }
-                                        }
-                                    }
-                                }
-
-                                // RemoveDirectory on a symbolic link will
-                                // remove the link itself.
-                                String reparsePoint = Path.Combine(fullPath, data.cFileName);
-                                r = Win32Native.RemoveDirectory(reparsePoint);
-                                if (!r) {
-                                    hr = Marshal.GetLastWin32Error();
-                                    if (hr != Win32Native.ERROR_PATH_NOT_FOUND) {
-                                        try {
-                                            __Error.WinIOError(hr, data.cFileName);
-                                        }
-                                        catch(Exception e) {
-                                            if (ex == null) {
-                                                ex = e;
-                                            }
-                                        }
-                                    }
-                                }
-                            }
-                        }
-                        else {
-                            String fileName = Path.Combine(fullPath, data.cFileName);
-                            r = Win32Native.DeleteFile(fileName);
-                            if (!r) {
-                                hr = Marshal.GetLastWin32Error();
-                                if (hr != Win32Native.ERROR_FILE_NOT_FOUND) {
-                                    try {
-                                        __Error.WinIOError(hr, data.cFileName);
-                                    }
-                                    catch (Exception e) {
-                                        if (ex == null) {
-                                            ex = e;
-                                        }
-                                    }
-                                }
-                            }
-                        }
-                    } while (Win32Native.FindNextFile(hnd, data));
-                    // Make sure we quit with a sensible error.
-                    hr = Marshal.GetLastWin32Error();
-                }
-
-                if (ex != null) 
-                    throw ex;
-                if (hr!=0 && hr!=Win32Native.ERROR_NO_MORE_FILES) 
-                    __Error.WinIOError(hr, userPath);
-            }
-
-            r = Win32Native.RemoveDirectory(fullPath);
-            
-            if (!r) {
-                hr = Marshal.GetLastWin32Error();
-                if (hr == Win32Native.ERROR_FILE_NOT_FOUND) // A dubious error code.
-                    hr = Win32Native.ERROR_PATH_NOT_FOUND;
-                // This check was originally put in for Win9x (unfortunately without special casing it to be for Win9x only). We can't change the NT codepath now for backcomp reasons.
-                if (hr == Win32Native.ERROR_ACCESS_DENIED) 
-                    throw new IOException(Environment.GetResourceString("UnauthorizedAccess_IODenied_Path", userPath));
-
-                // don't throw the DirectoryNotFoundException since this is a subdir and there could be a race condition
-                // between two Directory.Delete callers
-                if (hr == Win32Native.ERROR_PATH_NOT_FOUND && !throwOnTopLevelDirectoryNotFound)
-                    return;  
-
-                __Error.WinIOError(hr, fullPath);
-            }
-        }
     }
 }
 
diff --git a/src/mscorlib/src/System/IO/DirectoryInfo.cs b/src/mscorlib/src/System/IO/DirectoryInfo.cs
deleted file mode 100644
index c4c350d245..0000000000
--- a/src/mscorlib/src/System/IO/DirectoryInfo.cs
+++ /dev/null
@@ -1,511 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-// See the LICENSE file in the project root for more information.
-
-/*============================================================
-**
-** 
-** 
-**
-**
-** Purpose: Exposes routines for enumerating through a 
-** directory.
-**
-**          April 11,2000
-**
-===========================================================*/
-
-using System.Collections.Generic;
-using Microsoft.Win32;
-using System.Runtime.InteropServices;
-using System.Runtime.Serialization;
-using System.Runtime.Versioning;
-using System.Diagnostics;
-using System.Diagnostics.Contracts;
-
-namespace System.IO
-{
-    [Serializable]
-    [ComVisible(true)]
-    public sealed class DirectoryInfo : FileSystemInfo
-    {
-        // Migrating InheritanceDemands requires this default ctor, so we can annotate it.
-        private DirectoryInfo(){}
-
-        public DirectoryInfo(String path)
-        {
-            if (path==null)
-                throw new ArgumentNullException(nameof(path));
-            Contract.EndContractBlock();
-
-            Init(path);
-        }
-
-        private void Init(String path)
-        {
-            // Special case "<DriveLetter>:" to point to "<CurrentDirectory>" instead
-            if ((path.Length == 2) && (path[1] == ':'))
-            {
-                OriginalPath = ".";
-            }
-            else
-            {
-                OriginalPath = path;
-            }
-
-            FullPath = Path.GetFullPath(path); ;
-            DisplayPath = GetDisplayName(OriginalPath, FullPath);
-        }
-
-        internal DirectoryInfo(String fullPath, bool junk)
-        {
-            Debug.Assert(PathInternal.GetRootLength(fullPath) > 0, "fullPath must be fully qualified!");
-            // Fast path when we know a DirectoryInfo exists.
-            OriginalPath = Path.GetFileName(fullPath);
-
-            FullPath = fullPath;
-            DisplayPath = GetDisplayName(OriginalPath, FullPath);
-        }
-
-        private DirectoryInfo(SerializationInfo info, StreamingContext context) : base(info, context)
-        {
-            DisplayPath = GetDisplayName(OriginalPath, FullPath);
-        }
-
-        public override String Name
-        {
-            get 
-            {
-                // DisplayPath is dir name for coreclr
-                return DisplayPath;
-            }
-        }
-
-        public DirectoryInfo Parent {
-            get {
-                String parentName;
-                // FullPath might be either "c:\bar" or "c:\bar\".  Handle 
-                // those cases, as well as avoiding mangling "c:\".
-                String s = FullPath;
-                if (s.Length > 3 && s.EndsWith(Path.DirectorySeparatorChar))
-                    s = FullPath.Substring(0, FullPath.Length - 1);
-                parentName = Path.GetDirectoryName(s);
-                if (parentName==null)
-                    return null;
-
-                return new DirectoryInfo(parentName, false);
-            }
-        }
-
-        public DirectoryInfo CreateSubdirectory(String path) {
-            if (path == null)
-                throw new ArgumentNullException(nameof(path));
-            Contract.EndContractBlock();
-
-            return CreateSubdirectory(path, null);
-        }
-
-        public DirectoryInfo CreateSubdirectory(String path, Object directorySecurity)
-        {
-            if (path == null)
-                throw new ArgumentNullException(nameof(path));
-            Contract.EndContractBlock();
-
-            return CreateSubdirectoryHelper(path, directorySecurity);
-        }
-
-        private DirectoryInfo CreateSubdirectoryHelper(String path, Object directorySecurity)
-        {
-            Contract.Requires(path != null);
-
-            String newDirs = Path.Combine(FullPath, path);
-            String fullPath = Path.GetFullPath(newDirs);
-
-            if (0!=String.Compare(FullPath,0,fullPath,0, FullPath.Length,StringComparison.OrdinalIgnoreCase)) {
-                String displayPath = __Error.GetDisplayablePath(DisplayPath, false);
-                throw new ArgumentException(Environment.GetResourceString("Argument_InvalidSubPath", path, displayPath));
-            }
-
-            Directory.InternalCreateDirectory(fullPath, path, directorySecurity);
-
-            // Check for read permission to directory we hand back by calling this constructor.
-            return new DirectoryInfo(fullPath);
-        }
-
-        public void Create()
-        {
-            Directory.InternalCreateDirectory(FullPath, OriginalPath, null);
-        }
-
-        // Tests if the given path refers to an existing DirectoryInfo on disk.
-        public override bool Exists {
-            get
-            {
-                try
-                {
-                    if (_dataInitialised == -1)
-                        Refresh();
-                    if (_dataInitialised != 0) // Refresh was unable to initialise the data
-                        return false;
-                    return _data.fileAttributes != -1 && (_data.fileAttributes & Win32Native.FILE_ATTRIBUTE_DIRECTORY) != 0;
-                }
-                catch
-                {
-                    return false;
-                }
-            }
-        }
-
-        // Returns an array of Files in the current DirectoryInfo matching the 
-        // given search criteria (ie, "*.txt").
-        public FileInfo[] GetFiles(String searchPattern)
-        {
-            if (searchPattern == null)
-                throw new ArgumentNullException(nameof(searchPattern));
-            Contract.EndContractBlock();
-
-            return InternalGetFiles(searchPattern, SearchOption.TopDirectoryOnly);
-        }
-
-        // Returns an array of Files in the current DirectoryInfo matching the 
-        // given search criteria (ie, "*.txt").
-        public FileInfo[] GetFiles(String searchPattern, SearchOption searchOption)
-        {
-            if (searchPattern == null)
-                throw new ArgumentNullException(nameof(searchPattern));
-            if ((searchOption != SearchOption.TopDirectoryOnly) && (searchOption != SearchOption.AllDirectories))
-                throw new ArgumentOutOfRangeException(nameof(searchOption), Environment.GetResourceString("ArgumentOutOfRange_Enum"));
-            Contract.EndContractBlock();
-
-            return InternalGetFiles(searchPattern, searchOption);
-        }
-
-        // Returns an array of Files in the current DirectoryInfo matching the 
-        // given search criteria (ie, "*.txt").
-        private FileInfo[] InternalGetFiles(String searchPattern, SearchOption searchOption)
-        {
-            Contract.Requires(searchPattern != null);
-            Contract.Requires(searchOption == SearchOption.AllDirectories || searchOption == SearchOption.TopDirectoryOnly);
-
-            IEnumerable<FileInfo> enble = FileSystemEnumerableFactory.CreateFileInfoIterator(FullPath, OriginalPath, searchPattern, searchOption);
-            List<FileInfo> fileList = new List<FileInfo>(enble);
-            return fileList.ToArray();
-        }
-
-        // Returns an array of Files in the DirectoryInfo specified by path
-        public FileInfo[] GetFiles()
-        {
-            return InternalGetFiles("*", SearchOption.TopDirectoryOnly);
-        }
-
-        // Returns an array of Directories in the current directory.
-        public DirectoryInfo[] GetDirectories()
-        {
-            return InternalGetDirectories("*", SearchOption.TopDirectoryOnly);
-        }
-
-        // Returns an array of strongly typed FileSystemInfo entries in the path with the
-        // given search criteria (ie, "*.txt").
-        public FileSystemInfo[] GetFileSystemInfos(String searchPattern)
-        {
-            if (searchPattern == null)
-                throw new ArgumentNullException(nameof(searchPattern));
-            Contract.EndContractBlock();
-
-            return InternalGetFileSystemInfos(searchPattern, SearchOption.TopDirectoryOnly);
-        }
-
-        // Returns an array of strongly typed FileSystemInfo entries in the path with the
-        // given search criteria (ie, "*.txt").
-        public FileSystemInfo[] GetFileSystemInfos(String searchPattern, SearchOption searchOption)
-        {
-            if (searchPattern == null)
-                throw new ArgumentNullException(nameof(searchPattern));
-            if ((searchOption != SearchOption.TopDirectoryOnly) && (searchOption != SearchOption.AllDirectories))
-                throw new ArgumentOutOfRangeException(nameof(searchOption), Environment.GetResourceString("ArgumentOutOfRange_Enum"));
-            Contract.EndContractBlock();
-
-            return InternalGetFileSystemInfos(searchPattern, searchOption);
-        }
-
-        // Returns an array of strongly typed FileSystemInfo entries in the path with the
-        // given search criteria (ie, "*.txt").
-        private FileSystemInfo[] InternalGetFileSystemInfos(String searchPattern, SearchOption searchOption)
-        {
-            Contract.Requires(searchPattern != null);
-            Contract.Requires(searchOption == SearchOption.AllDirectories || searchOption == SearchOption.TopDirectoryOnly);
-
-            IEnumerable<FileSystemInfo> enble = FileSystemEnumerableFactory.CreateFileSystemInfoIterator(FullPath, OriginalPath, searchPattern, searchOption);
-            List<FileSystemInfo> fileList = new List<FileSystemInfo>(enble);
-            return fileList.ToArray();
-        }
-
-        // Returns an array of strongly typed FileSystemInfo entries which will contain a listing
-        // of all the files and directories.
-        public FileSystemInfo[] GetFileSystemInfos()
-        {
-            return InternalGetFileSystemInfos("*", SearchOption.TopDirectoryOnly);
-        }
-
-        // Returns an array of Directories in the current DirectoryInfo matching the 
-        // given search criteria (ie, "System*" could match the System & System32
-        // directories).
-        public DirectoryInfo[] GetDirectories(String searchPattern)
-        {
-            if (searchPattern == null)
-                throw new ArgumentNullException(nameof(searchPattern));
-            Contract.EndContractBlock();
-
-            return InternalGetDirectories(searchPattern, SearchOption.TopDirectoryOnly);
-        }
-
-        // Returns an array of Directories in the current DirectoryInfo matching the 
-        // given search criteria (ie, "System*" could match the System & System32
-        // directories).
-        public DirectoryInfo[] GetDirectories(String searchPattern, SearchOption searchOption)
-        {
-            if (searchPattern == null)
-                throw new ArgumentNullException(nameof(searchPattern));
-            if ((searchOption != SearchOption.TopDirectoryOnly) && (searchOption != SearchOption.AllDirectories))
-                throw new ArgumentOutOfRangeException(nameof(searchOption), Environment.GetResourceString("ArgumentOutOfRange_Enum"));
-            Contract.EndContractBlock();
-
-            return InternalGetDirectories(searchPattern, searchOption);
-        }
-
-        // Returns an array of Directories in the current DirectoryInfo matching the 
-        // given search criteria (ie, "System*" could match the System & System32
-        // directories).
-        private DirectoryInfo[] InternalGetDirectories(String searchPattern, SearchOption searchOption)
-        {
-            Contract.Requires(searchPattern != null);
-            Contract.Requires(searchOption == SearchOption.AllDirectories || searchOption == SearchOption.TopDirectoryOnly);
-
-            IEnumerable<DirectoryInfo> enble = FileSystemEnumerableFactory.CreateDirectoryInfoIterator(FullPath, OriginalPath, searchPattern, searchOption);
-            List<DirectoryInfo> fileList = new List<DirectoryInfo>(enble);
-            return fileList.ToArray();
-        }
-
-        public IEnumerable<DirectoryInfo> EnumerateDirectories()
-        {
-            return InternalEnumerateDirectories("*", SearchOption.TopDirectoryOnly);
-        }
-
-        public IEnumerable<DirectoryInfo> EnumerateDirectories(String searchPattern)
-        {
-            if (searchPattern == null)
-                throw new ArgumentNullException(nameof(searchPattern));
-            Contract.EndContractBlock();
-
-            return InternalEnumerateDirectories(searchPattern, SearchOption.TopDirectoryOnly);
-        }
-
-        public IEnumerable<DirectoryInfo> EnumerateDirectories(String searchPattern, SearchOption searchOption)
-        {
-            if (searchPattern == null)
-                throw new ArgumentNullException(nameof(searchPattern));
-            if ((searchOption != SearchOption.TopDirectoryOnly) && (searchOption != SearchOption.AllDirectories))
-                throw new ArgumentOutOfRangeException(nameof(searchOption), Environment.GetResourceString("ArgumentOutOfRange_Enum"));
-            Contract.EndContractBlock();
-
-            return InternalEnumerateDirectories(searchPattern, searchOption);
-        }
-
-        private IEnumerable<DirectoryInfo> InternalEnumerateDirectories(String searchPattern, SearchOption searchOption)
-        {
-            Contract.Requires(searchPattern != null);
-            Contract.Requires(searchOption == SearchOption.AllDirectories || searchOption == SearchOption.TopDirectoryOnly);
-
-            return FileSystemEnumerableFactory.CreateDirectoryInfoIterator(FullPath, OriginalPath, searchPattern, searchOption);
-        }
-
-        public IEnumerable<FileInfo> EnumerateFiles()
-        {
-            return InternalEnumerateFiles("*", SearchOption.TopDirectoryOnly);
-        }
-
-        public IEnumerable<FileInfo> EnumerateFiles(String searchPattern)
-        {
-            if (searchPattern == null)
-                throw new ArgumentNullException(nameof(searchPattern));
-            Contract.EndContractBlock();
-
-            return InternalEnumerateFiles(searchPattern, SearchOption.TopDirectoryOnly);
-        }
-
-        public IEnumerable<FileInfo> EnumerateFiles(String searchPattern, SearchOption searchOption)
-        {
-            if (searchPattern == null)
-                throw new ArgumentNullException(nameof(searchPattern));
-            if ((searchOption != SearchOption.TopDirectoryOnly) && (searchOption != SearchOption.AllDirectories))
-                throw new ArgumentOutOfRangeException(nameof(searchOption), Environment.GetResourceString("ArgumentOutOfRange_Enum"));
-            Contract.EndContractBlock();
-
-            return InternalEnumerateFiles(searchPattern, searchOption);
-        }
-
-        private IEnumerable<FileInfo> InternalEnumerateFiles(String searchPattern, SearchOption searchOption)
-        {
-            Contract.Requires(searchPattern != null);
-            Contract.Requires(searchOption == SearchOption.AllDirectories || searchOption == SearchOption.TopDirectoryOnly);
-
-            return FileSystemEnumerableFactory.CreateFileInfoIterator(FullPath, OriginalPath, searchPattern, searchOption);
-        }
-
-        public IEnumerable<FileSystemInfo> EnumerateFileSystemInfos()
-        {
-            return InternalEnumerateFileSystemInfos("*", SearchOption.TopDirectoryOnly);
-        }
-
-        public IEnumerable<FileSystemInfo> EnumerateFileSystemInfos(String searchPattern)
-        {
-            if (searchPattern == null)
-                throw new ArgumentNullException(nameof(searchPattern));
-            Contract.EndContractBlock();
-
-            return InternalEnumerateFileSystemInfos(searchPattern, SearchOption.TopDirectoryOnly);
-        }
-
-        public IEnumerable<FileSystemInfo> EnumerateFileSystemInfos(String searchPattern, SearchOption searchOption)
-        {
-            if (searchPattern == null)
-                throw new ArgumentNullException(nameof(searchPattern));
-            if ((searchOption != SearchOption.TopDirectoryOnly) && (searchOption != SearchOption.AllDirectories))
-                throw new ArgumentOutOfRangeException(nameof(searchOption), Environment.GetResourceString("ArgumentOutOfRange_Enum"));
-            Contract.EndContractBlock();
-
-            return InternalEnumerateFileSystemInfos(searchPattern, searchOption);
-        }
-
-        private IEnumerable<FileSystemInfo> InternalEnumerateFileSystemInfos(String searchPattern, SearchOption searchOption)
-        {
-            Contract.Requires(searchPattern != null);
-            Contract.Requires(searchOption == SearchOption.AllDirectories || searchOption == SearchOption.TopDirectoryOnly);
-
-            return FileSystemEnumerableFactory.CreateFileSystemInfoIterator(FullPath, OriginalPath, searchPattern, searchOption);
-        }
-
-        // Returns the root portion of the given path. The resulting string
-        // consists of those rightmost characters of the path that constitute the
-        // root of the path. Possible patterns for the resulting string are: An
-        // empty string (a relative path on the current drive), "\" (an absolute
-        // path on the current drive), "X:" (a relative path on a given drive,
-        // where X is the drive letter), "X:\" (an absolute path on a given drive),
-        // and "\\server\share" (a UNC path for a given server and share name).
-        // The resulting string is null if path is null.
-        public DirectoryInfo Root {
-            get
-            {
-                int rootLength = PathInternal.GetRootLength(FullPath);
-                String rootPath = FullPath.Substring(0, rootLength);
-
-                return new DirectoryInfo(rootPath);
-            }
-        }
-
-        public void MoveTo(String destDirName) {
-            if (destDirName==null)
-                throw new ArgumentNullException(nameof(destDirName));
-            if (destDirName.Length==0)
-                throw new ArgumentException(Environment.GetResourceString("Argument_EmptyFileName"), nameof(destDirName));
-            Contract.EndContractBlock();
-
-            String fullDestDirName = Path.GetFullPath(destDirName);
-            if (!fullDestDirName.EndsWith(Path.DirectorySeparatorChar))
-                fullDestDirName = fullDestDirName + Path.DirectorySeparatorChar;
-
-            String fullSourcePath;
-            if (FullPath.EndsWith(Path.DirectorySeparatorChar))
-                fullSourcePath = FullPath;
-            else
-                fullSourcePath = FullPath + Path.DirectorySeparatorChar;
-
-            if (String.Compare(fullSourcePath, fullDestDirName, StringComparison.OrdinalIgnoreCase) == 0)
-                throw new IOException(Environment.GetResourceString("IO.IO_SourceDestMustBeDifferent"));
-
-            String sourceRoot = Path.GetPathRoot(fullSourcePath);
-            String destinationRoot = Path.GetPathRoot(fullDestDirName);
-
-            if (String.Compare(sourceRoot, destinationRoot, StringComparison.OrdinalIgnoreCase) != 0)
-                throw new IOException(Environment.GetResourceString("IO.IO_SourceDestMustHaveSameRoot"));
-                       
-            if (!Win32Native.MoveFile(FullPath, destDirName))
-            {
-                int hr = Marshal.GetLastWin32Error();
-                if (hr == Win32Native.ERROR_FILE_NOT_FOUND) // A dubious error code
-                {
-                    hr = Win32Native.ERROR_PATH_NOT_FOUND;
-                    __Error.WinIOError(hr, DisplayPath);
-                }
-                
-                if (hr == Win32Native.ERROR_ACCESS_DENIED) // We did this for Win9x. We can't change it for backcomp. 
-                    throw new IOException(Environment.GetResourceString("UnauthorizedAccess_IODenied_Path", DisplayPath));
-            
-                __Error.WinIOError(hr,String.Empty);
-            }
-            FullPath = fullDestDirName;
-            OriginalPath = destDirName;
-            DisplayPath = GetDisplayName(OriginalPath, FullPath);
-
-            // Flush any cached information about the directory.
-            _dataInitialised = -1;
-        }
-
-        public override void Delete()
-        {
-            Directory.Delete(FullPath, OriginalPath, false);
-        }
-
-        public void Delete(bool recursive)
-        {
-            Directory.Delete(FullPath, OriginalPath, recursive);
-        }
-
-        // Returns the fully qualified path
-        public override String ToString()
-        {
-            return DisplayPath;
-        }
-
-        private static String GetDisplayName(String originalPath, String fullPath)
-        {
-            Debug.Assert(originalPath != null);
-            Debug.Assert(fullPath != null);
-
-            String displayName = "";
-
-            // Special case "<DriveLetter>:" to point to "<CurrentDirectory>" instead
-            if ((originalPath.Length == 2) && (originalPath[1] == ':'))
-            {
-                displayName = ".";
-            }
-            else 
-            {
-                displayName = GetDirName(fullPath);
-            }
-            return displayName;
-        }
-
-        private static String GetDirName(String fullPath)
-        {
-            Debug.Assert(fullPath != null);
-
-            String dirName = null;
-            if (fullPath.Length > 3)
-            {
-                String s = fullPath;
-                if (fullPath.EndsWith(Path.DirectorySeparatorChar))
-                {
-                    s = fullPath.Substring(0, fullPath.Length - 1);
-                }
-                dirName = Path.GetFileName(s);
-            }
-            else
-            {
-                dirName = fullPath;  // For rooted paths, like "c:\"
-            }
-            return dirName;
-        }
-    }
-}
-
diff --git a/src/mscorlib/src/System/IO/DirectoryNotFoundException.cs b/src/mscorlib/src/System/IO/DirectoryNotFoundException.cs
index 09d7e7d4e7..21211a61e7 100644
--- a/src/mscorlib/src/System/IO/DirectoryNotFoundException.cs
+++ b/src/mscorlib/src/System/IO/DirectoryNotFoundException.cs
@@ -23,7 +23,6 @@ namespace System.IO {
      * and STG_E_PATHNOTFOUND (0x80030003).
      */
     [Serializable]
-    [System.Runtime.InteropServices.ComVisible(true)]
     public class DirectoryNotFoundException : IOException {
         public DirectoryNotFoundException() 
             : base(Environment.GetResourceString("Arg_DirectoryNotFoundException")) {
diff --git a/src/mscorlib/src/System/IO/DriveNotFoundException.cs b/src/mscorlib/src/System/IO/DriveNotFoundException.cs
index 04155bcc0e..f0245a8b28 100644
--- a/src/mscorlib/src/System/IO/DriveNotFoundException.cs
+++ b/src/mscorlib/src/System/IO/DriveNotFoundException.cs
@@ -17,8 +17,7 @@ namespace System.IO {
 
     //Thrown when trying to access a drive that is not availabe.
     [Serializable]
-    [System.Runtime.InteropServices.ComVisible(true)]
-    public class DriveNotFoundException : IOException {
+    internal class DriveNotFoundException : IOException {
         public DriveNotFoundException() 
             : base(Environment.GetResourceString("Arg_DriveNotFoundException")) {
             SetErrorCode(__HResults.COR_E_DIRECTORYNOTFOUND);
@@ -28,11 +27,6 @@ namespace System.IO {
             : base(message) {
             SetErrorCode(__HResults.COR_E_DIRECTORYNOTFOUND);
         }
-    
-        public DriveNotFoundException(String message, Exception innerException) 
-            : base(message, innerException) {
-            SetErrorCode(__HResults.COR_E_DIRECTORYNOTFOUND);
-        }
         
         protected DriveNotFoundException(SerializationInfo info, StreamingContext context) : base(info, context) {
         }
diff --git a/src/mscorlib/src/System/IO/EndOfStreamException.cs b/src/mscorlib/src/System/IO/EndOfStreamException.cs
index 60f5109a0f..558c792a9e 100644
--- a/src/mscorlib/src/System/IO/EndOfStreamException.cs
+++ b/src/mscorlib/src/System/IO/EndOfStreamException.cs
@@ -18,7 +18,6 @@ using System.Runtime.Serialization;
 
 namespace System.IO {
     [Serializable]
-    [System.Runtime.InteropServices.ComVisible(true)]
     public class EndOfStreamException : IOException
     {
         public EndOfStreamException() 
diff --git a/src/mscorlib/src/System/IO/File.cs b/src/mscorlib/src/System/IO/File.cs
index 9f89f81a91..7cc3f431a9 100644
--- a/src/mscorlib/src/System/IO/File.cs
+++ b/src/mscorlib/src/System/IO/File.cs
@@ -14,7 +14,6 @@
 **
 ===========================================================*/
 
-using System.Security.Permissions;
 using Win32Native = Microsoft.Win32.Win32Native;
 using System.Runtime.InteropServices;
 using System.Security;
@@ -28,155 +27,13 @@ namespace System.IO
 {
     // Class for creating FileStream objects, and some basic file management
     // routines such as Delete, etc.
-    [ComVisible(true)]
-    public static class File
+    internal static class File
     {
         private const int ERROR_INVALID_PARAMETER = 87;
         internal const int GENERIC_READ = unchecked((int)0x80000000);
 
         private const int GetFileExInfoStandard = 0;
 
-        public static StreamReader OpenText(String path)
-        {
-            if (path == null)
-                throw new ArgumentNullException(nameof(path));
-            Contract.EndContractBlock();
-            return new StreamReader(path);
-        }
-
-        public static StreamWriter CreateText(String path)
-        {
-            if (path == null)
-                throw new ArgumentNullException(nameof(path));
-            Contract.EndContractBlock();
-            return new StreamWriter(path,false);
-        }
-
-        public static StreamWriter AppendText(String path)
-        {
-            if (path == null)
-                throw new ArgumentNullException(nameof(path));
-            Contract.EndContractBlock();
-            return new StreamWriter(path,true);
-        }
-
-
-        // Copies an existing file to a new file. An exception is raised if the
-        // destination file already exists. Use the 
-        // Copy(String, String, boolean) method to allow 
-        // overwriting an existing file.
-        public static void Copy(String sourceFileName, String destFileName) {
-            if (sourceFileName == null)
-                throw new ArgumentNullException(nameof(sourceFileName), Environment.GetResourceString("ArgumentNull_FileName"));
-            if (destFileName == null)
-                throw new ArgumentNullException(nameof(destFileName), Environment.GetResourceString("ArgumentNull_FileName"));
-            if (sourceFileName.Length == 0)
-                throw new ArgumentException(Environment.GetResourceString("Argument_EmptyFileName"), nameof(sourceFileName));
-            if (destFileName.Length == 0)
-                throw new ArgumentException(Environment.GetResourceString("Argument_EmptyFileName"), nameof(destFileName));
-            Contract.EndContractBlock();
-
-            InternalCopy(sourceFileName, destFileName, false);
-        }
-    
-        // Copies an existing file to a new file. If overwrite is 
-        // false, then an IOException is thrown if the destination file 
-        // already exists.  If overwrite is true, the file is 
-        // overwritten.
-        public static void Copy(String sourceFileName, String destFileName, bool overwrite) {
-            if (sourceFileName == null)
-                throw new ArgumentNullException(nameof(sourceFileName), Environment.GetResourceString("ArgumentNull_FileName"));
-            if (destFileName == null)
-                throw new ArgumentNullException(nameof(destFileName), Environment.GetResourceString("ArgumentNull_FileName"));
-            if (sourceFileName.Length == 0)
-                throw new ArgumentException(Environment.GetResourceString("Argument_EmptyFileName"), nameof(sourceFileName));
-            if (destFileName.Length == 0)
-                throw new ArgumentException(Environment.GetResourceString("Argument_EmptyFileName"), nameof(destFileName));
-            Contract.EndContractBlock();
-
-            InternalCopy(sourceFileName, destFileName, overwrite);
-        }
-
-        /// <devdoc>
-        ///    Note: This returns the fully qualified name of the destination file.
-        /// </devdoc>
-        internal static String InternalCopy(String sourceFileName, String destFileName, bool overwrite)
-        {
-            Contract.Requires(sourceFileName != null);
-            Contract.Requires(destFileName != null);
-            Contract.Requires(sourceFileName.Length > 0);
-            Contract.Requires(destFileName.Length > 0);
-
-            String fullSourceFileName = Path.GetFullPath(sourceFileName);
-            String fullDestFileName = Path.GetFullPath(destFileName);
-
-            bool r = Win32Native.CopyFile(fullSourceFileName, fullDestFileName, !overwrite);
-            if (!r) {
-                // Save Win32 error because subsequent checks will overwrite this HRESULT.
-                int errorCode = Marshal.GetLastWin32Error();
-                String fileName = destFileName;
-
-                if (errorCode != Win32Native.ERROR_FILE_EXISTS) {
-                    if (errorCode == Win32Native.ERROR_ACCESS_DENIED) {
-                        if (Directory.InternalExists(fullDestFileName))
-                            throw new IOException(Environment.GetResourceString("Arg_FileIsDirectory_Name", destFileName), Win32Native.ERROR_ACCESS_DENIED, fullDestFileName);
-                    }
-                }
-
-                __Error.WinIOError(errorCode, fileName);
-            }
-
-            return fullDestFileName;
-        }
-
-        // Creates a file in a particular path.  If the file exists, it is replaced.
-        // The file is opened with ReadWrite accessand cannot be opened by another 
-        // application until it has been closed.  An IOException is thrown if the 
-        // directory specified doesn't exist.
-        public static FileStream Create(String path) {
-            return Create(path, FileStream.DefaultBufferSize);
-        }
-        
-        // Creates a file in a particular path.  If the file exists, it is replaced.
-        // The file is opened with ReadWrite access and cannot be opened by another 
-        // application until it has been closed.  An IOException is thrown if the 
-        // directory specified doesn't exist.
-        public static FileStream Create(String path, int bufferSize) {
-            return new FileStream(path, FileMode.Create, FileAccess.ReadWrite, FileShare.None, bufferSize);
-        }
-
-        public static FileStream Create(String path, int bufferSize, FileOptions options) {
-            return new FileStream(path, FileMode.Create, FileAccess.ReadWrite,
-                                  FileShare.None, bufferSize, options);
-        }
-
-        // Deletes a file. The file specified by the designated path is deleted.
-        // If the file does not exist, Delete succeeds without throwing
-        // an exception.
-        // 
-        // On NT, Delete will fail for a file that is open for normal I/O
-        // or a file that is memory mapped.  
-        public static void Delete(String path) {
-            if (path == null)
-                throw new ArgumentNullException(nameof(path));
-            Contract.EndContractBlock();
-
-            InternalDelete(path);
-        }
-
-        internal static void InternalDelete(String path)
-        {
-            String fullPath = Path.GetFullPath(path);
-            bool r = Win32Native.DeleteFile(fullPath);
-            if (!r) {
-                int hr = Marshal.GetLastWin32Error();
-                if (hr==Win32Native.ERROR_FILE_NOT_FOUND)
-                    return;
-                else
-                    __Error.WinIOError(hr, fullPath);
-            }
-        }
-
         // Tests if a file exists. The result is true if the file
         // given by the specified path exists; otherwise, the result is
         // false.  Note that if path describes a directory,
@@ -225,193 +82,11 @@ namespace System.IO
                     && ((data.fileAttributes  & Win32Native.FILE_ATTRIBUTE_DIRECTORY) == 0);
         }
 
-        public static FileStream Open(String path, FileMode mode) {
-            return Open(path, mode, (mode == FileMode.Append ? FileAccess.Write : FileAccess.ReadWrite), FileShare.None);
-        }
-
-        public static FileStream Open(String path, FileMode mode, FileAccess access) {
-            return Open(path,mode, access, FileShare.None);
-        }
-
-        public static FileStream Open(String path, FileMode mode, FileAccess access, FileShare share) {
-            return new FileStream(path, mode, access, share);
-        }
-
-        public static DateTime GetCreationTime(String path)
-        {
-            return InternalGetCreationTimeUtc(path).ToLocalTime();
-        }
-
-        public static DateTime GetCreationTimeUtc(String path)
-        {
-            return InternalGetCreationTimeUtc(path); // this API isn't exposed in Silverlight
-        }
-
-        private static DateTime InternalGetCreationTimeUtc(String path)
-        {
-            String fullPath = Path.GetFullPath(path);
-
-            Win32Native.WIN32_FILE_ATTRIBUTE_DATA data = new Win32Native.WIN32_FILE_ATTRIBUTE_DATA();
-            int dataInitialised = FillAttributeInfo(fullPath, ref data, false, false);
-            if (dataInitialised != 0)
-                __Error.WinIOError(dataInitialised, fullPath);
-
-            long dt = ((long)(data.ftCreationTimeHigh) << 32) | ((long)data.ftCreationTimeLow);
-            return DateTime.FromFileTimeUtc(dt);
-        }
-
-        public static DateTime GetLastAccessTime(String path)
-        {
-            return InternalGetLastAccessTimeUtc(path).ToLocalTime();
-        }
-
-        public static DateTime GetLastAccessTimeUtc(String path)
-        {
-            return InternalGetLastAccessTimeUtc(path);
-        }
-
-        private static DateTime InternalGetLastAccessTimeUtc(String path)
-        {
-            String fullPath = Path.GetFullPath(path);
-
-            Win32Native.WIN32_FILE_ATTRIBUTE_DATA data = new Win32Native.WIN32_FILE_ATTRIBUTE_DATA();
-            int dataInitialised = FillAttributeInfo(fullPath, ref data, false, false);
-            if (dataInitialised != 0)
-                __Error.WinIOError(dataInitialised, fullPath);
-
-            long dt = ((long)(data.ftLastAccessTimeHigh) << 32) | ((long)data.ftLastAccessTimeLow);
-            return DateTime.FromFileTimeUtc(dt);
-        }
-
-        public static DateTime GetLastWriteTime(String path)
-        {
-            return InternalGetLastWriteTimeUtc(path).ToLocalTime();
-        }
-
-        public static DateTime GetLastWriteTimeUtc(String path)
-        {
-            return InternalGetLastWriteTimeUtc(path);
-        }
-
-        private static DateTime InternalGetLastWriteTimeUtc(String path)
-        {
-            String fullPath = Path.GetFullPath(path);
-
-            Win32Native.WIN32_FILE_ATTRIBUTE_DATA data = new Win32Native.WIN32_FILE_ATTRIBUTE_DATA();
-            int dataInitialised = FillAttributeInfo(fullPath, ref data, false, false);
-            if (dataInitialised != 0)
-                __Error.WinIOError(dataInitialised, fullPath);
-
-            long dt = ((long)data.ftLastWriteTimeHigh << 32) | ((long)data.ftLastWriteTimeLow);
-            return DateTime.FromFileTimeUtc(dt);
-        }
-
-        public static FileAttributes GetAttributes(String path) 
-        {
-            String fullPath = Path.GetFullPath(path);
-
-            Win32Native.WIN32_FILE_ATTRIBUTE_DATA data = new Win32Native.WIN32_FILE_ATTRIBUTE_DATA();
-            int dataInitialised = FillAttributeInfo(fullPath, ref data, false, true);
-            if (dataInitialised != 0)
-                __Error.WinIOError(dataInitialised, fullPath);
-
-            return (FileAttributes) data.fileAttributes;
-        }
-
-        public static void SetAttributes(String path, FileAttributes fileAttributes) 
-        {
-            String fullPath = Path.GetFullPath(path);
-            bool r = Win32Native.SetFileAttributes(fullPath, (int) fileAttributes);
-            if (!r) {
-                int hr = Marshal.GetLastWin32Error();
-                if (hr==ERROR_INVALID_PARAMETER)
-                    throw new ArgumentException(Environment.GetResourceString("Arg_InvalidFileAttrs"));
-                 __Error.WinIOError(hr, fullPath);
-            }
-        }
-
-        public static FileStream OpenRead(String path) {
-            return new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read);
-        }
-
-        public static FileStream OpenWrite(String path) {
-            return new FileStream(path, FileMode.OpenOrCreate, 
-                                  FileAccess.Write, FileShare.None);
-        }
-
-        public static String ReadAllText(String path)
-        {
-            if (path == null)
-                throw new ArgumentNullException(nameof(path));
-            if (path.Length == 0)
-                throw new ArgumentException(Environment.GetResourceString("Argument_EmptyPath"));
-            Contract.EndContractBlock();
-
-            return InternalReadAllText(path, Encoding.UTF8);
-        }
-
-        public static String ReadAllText(String path, Encoding encoding)
-        {
-            if (path == null)
-                throw new ArgumentNullException(nameof(path));
-            if (encoding == null)
-                throw new ArgumentNullException(nameof(encoding));
-            if (path.Length == 0)
-                throw new ArgumentException(Environment.GetResourceString("Argument_EmptyPath"));
-            Contract.EndContractBlock();
-
-            return InternalReadAllText(path, encoding);
-        }
-
-        private static String InternalReadAllText(String path, Encoding encoding)
-        {
-            Contract.Requires(path != null);
-            Contract.Requires(encoding != null);
-            Contract.Requires(path.Length > 0);
-
-            using (StreamReader sr = new StreamReader(path, encoding, true, StreamReader.DefaultBufferSize))
-                return sr.ReadToEnd();
-        }
-
-        public static void WriteAllText(String path, String contents)
-        {
-            if (path == null)
-                throw new ArgumentNullException(nameof(path));
-            if (path.Length == 0)
-                throw new ArgumentException(Environment.GetResourceString("Argument_EmptyPath"));
-            Contract.EndContractBlock();
-
-            InternalWriteAllText(path, contents, StreamWriter.UTF8NoBOM);
-        }
-
-        public static void WriteAllText(String path, String contents, Encoding encoding)
-        {
-            if (path == null)
-                throw new ArgumentNullException(nameof(path));
-            if (encoding == null)
-                throw new ArgumentNullException(nameof(encoding));
-            if (path.Length == 0)
-                throw new ArgumentException(Environment.GetResourceString("Argument_EmptyPath"));
-            Contract.EndContractBlock();
-
-            InternalWriteAllText(path, contents, encoding);
-        }
-
-        private static void InternalWriteAllText(String path, String contents, Encoding encoding)
-        {
-            Contract.Requires(path != null);
-            Contract.Requires(encoding != null);
-            Contract.Requires(path.Length > 0);
-
-            using (StreamWriter sw = new StreamWriter(path, false, encoding, StreamWriter.DefaultBufferSize))
-                sw.Write(contents);
-        } 
-
         public static byte[] ReadAllBytes(String path)
         {
             byte[] bytes;
             using(FileStream fs = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, 
-                FileStream.DefaultBufferSize, FileOptions.None, Path.GetFileName(path), false, false)) {
+                FileStream.DefaultBufferSize, FileOptions.None)) {
                 // Do a blocking read
                 int index = 0;
                 long fileLength = fs.Length;
@@ -430,32 +105,7 @@ namespace System.IO
             return bytes;
         }
 
-        public static void WriteAllBytes(String path, byte[] bytes)
-        {
-            if (path == null)
-                throw new ArgumentNullException(nameof(path), Environment.GetResourceString("ArgumentNull_Path"));
-            if (path.Length == 0)
-                throw new ArgumentException(Environment.GetResourceString("Argument_EmptyPath"));
-            if (bytes == null)
-                throw new ArgumentNullException(nameof(bytes));
-            Contract.EndContractBlock();
-
-            InternalWriteAllBytes(path, bytes);
-        }
-
-        private static void InternalWriteAllBytes(String path, byte[] bytes)
-        {
-            Contract.Requires(path != null);
-            Contract.Requires(path.Length != 0);
-            Contract.Requires(bytes != null);
-
-            using (FileStream fs = new FileStream(path, FileMode.Create, FileAccess.Write, FileShare.Read,
-                    FileStream.DefaultBufferSize, FileOptions.None, Path.GetFileName(path), false, false))
-            {
-                fs.Write(bytes, 0, bytes.Length);
-            }
-        }
-
+#if PLATFORM_UNIX
         public static String[] ReadAllLines(String path)
         {
             if (path == null)
@@ -467,19 +117,6 @@ namespace System.IO
             return InternalReadAllLines(path, Encoding.UTF8);
         }
 
-        public static String[] ReadAllLines(String path, Encoding encoding)
-        {
-            if (path == null)
-                throw new ArgumentNullException(nameof(path));
-            if (encoding == null)
-                throw new ArgumentNullException(nameof(encoding));
-            if (path.Length == 0)
-                throw new ArgumentException(Environment.GetResourceString("Argument_EmptyPath"));
-            Contract.EndContractBlock();
-
-            return InternalReadAllLines(path, encoding);
-        }
-
         private static String[] InternalReadAllLines(String path, Encoding encoding)
         {
             Contract.Requires(path != null);
@@ -495,236 +132,8 @@ namespace System.IO
 
             return lines.ToArray();
         }
-
-        public static IEnumerable<String> ReadLines(String path)
-        {
-            if (path == null)
-                throw new ArgumentNullException(nameof(path));
-            if (path.Length == 0)
-                throw new ArgumentException(Environment.GetResourceString("Argument_EmptyPath"), nameof(path));
-            Contract.EndContractBlock();
-
-            return ReadLinesIterator.CreateIterator(path, Encoding.UTF8);
-        }
-
-        public static IEnumerable<String> ReadLines(String path, Encoding encoding)
-        {
-            if (path == null)
-                throw new ArgumentNullException(nameof(path));
-            if (encoding == null)
-                throw new ArgumentNullException(nameof(encoding));
-            if (path.Length == 0)
-                throw new ArgumentException(Environment.GetResourceString("Argument_EmptyPath"), nameof(path));
-            Contract.EndContractBlock();
-
-            return ReadLinesIterator.CreateIterator(path, encoding);
-        }
-
-        public static void WriteAllLines(String path, String[] contents)
-        {
-            if (path == null)
-                throw new ArgumentNullException(nameof(path));
-            if (contents == null)
-                throw new ArgumentNullException(nameof(contents));
-            if (path.Length == 0)
-                throw new ArgumentException(Environment.GetResourceString("Argument_EmptyPath"));
-            Contract.EndContractBlock();
-
-            InternalWriteAllLines(new StreamWriter(path, false, StreamWriter.UTF8NoBOM), contents);
-        }
-
-        public static void WriteAllLines(String path, String[] contents, Encoding encoding)
-        {
-            if (path == null)
-                throw new ArgumentNullException(nameof(path));
-            if (contents == null)
-                throw new ArgumentNullException(nameof(contents));
-            if (encoding == null)
-                throw new ArgumentNullException(nameof(encoding));
-            if (path.Length == 0)
-                throw new ArgumentException(Environment.GetResourceString("Argument_EmptyPath"));
-            Contract.EndContractBlock();
-
-            InternalWriteAllLines(new StreamWriter(path, false, encoding), contents);
-        }
-
-        public static void WriteAllLines(String path, IEnumerable<String> contents)
-        {
-            if (path == null)
-                throw new ArgumentNullException(nameof(path));
-            if (contents == null)
-                throw new ArgumentNullException(nameof(contents));
-            if (path.Length == 0)
-                throw new ArgumentException(Environment.GetResourceString("Argument_EmptyPath"));
-            Contract.EndContractBlock();
-
-            InternalWriteAllLines(new StreamWriter(path, false, StreamWriter.UTF8NoBOM), contents);
-        }
-
-        public static void WriteAllLines(String path, IEnumerable<String> contents, Encoding encoding)
-        {
-            if (path == null)
-                throw new ArgumentNullException(nameof(path));
-            if (contents == null)
-                throw new ArgumentNullException(nameof(contents));
-            if (encoding == null)
-                throw new ArgumentNullException(nameof(encoding));
-            if (path.Length == 0)
-                throw new ArgumentException(Environment.GetResourceString("Argument_EmptyPath"));
-            Contract.EndContractBlock();
-
-            InternalWriteAllLines(new StreamWriter(path, false, encoding), contents);
-        }
-
-        private static void InternalWriteAllLines(TextWriter writer, IEnumerable<String> contents)
-        {
-            Contract.Requires(writer != null);
-            Contract.Requires(contents != null);
-
-            using (writer)
-            {
-                foreach (String line in contents)
-                {
-                    writer.WriteLine(line);
-                }
-            }
-        }
-
-        public static void AppendAllText(String path, String contents)
-        {
-            if (path == null)
-                throw new ArgumentNullException(nameof(path));
-            if (path.Length == 0)
-                throw new ArgumentException(Environment.GetResourceString("Argument_EmptyPath"));
-            Contract.EndContractBlock();
-
-            InternalAppendAllText(path, contents, StreamWriter.UTF8NoBOM);
-        }
-
-        public static void AppendAllText(String path, String contents, Encoding encoding)
-        {
-            if (path == null)
-                throw new ArgumentNullException(nameof(path));
-            if (encoding == null)
-                throw new ArgumentNullException(nameof(encoding));
-            if (path.Length == 0)
-                throw new ArgumentException(Environment.GetResourceString("Argument_EmptyPath"));
-            Contract.EndContractBlock();
-
-            InternalAppendAllText(path, contents, encoding);
-        }
-
-        private static void InternalAppendAllText(String path, String contents, Encoding encoding)
-        {
-            Contract.Requires(path != null);
-            Contract.Requires(encoding != null);
-            Contract.Requires(path.Length > 0);
-
-            using (StreamWriter sw = new StreamWriter(path, true, encoding))
-                sw.Write(contents);
-        }
-
-        public static void AppendAllLines(String path, IEnumerable<String> contents)
-        {
-            if (path == null)
-                throw new ArgumentNullException(nameof(path));
-            if (contents == null)
-                throw new ArgumentNullException(nameof(contents));
-            if (path.Length == 0)
-                throw new ArgumentException(Environment.GetResourceString("Argument_EmptyPath"));
-            Contract.EndContractBlock();
-
-            InternalWriteAllLines(new StreamWriter(path, true, StreamWriter.UTF8NoBOM), contents);
-        }
-
-        public static void AppendAllLines(String path, IEnumerable<String> contents, Encoding encoding)
-        {
-            if (path == null)
-                throw new ArgumentNullException(nameof(path));
-            if (contents == null)
-                throw new ArgumentNullException(nameof(contents));
-            if (encoding == null)
-                throw new ArgumentNullException(nameof(encoding));
-            if (path.Length == 0)
-                throw new ArgumentException(Environment.GetResourceString("Argument_EmptyPath"));
-            Contract.EndContractBlock();
-
-            InternalWriteAllLines(new StreamWriter(path, true, encoding), contents);
-        }
-
-        // Moves a specified file to a new location and potentially a new file name.
-        // This method does work across volumes.
-        public static void Move(String sourceFileName, String destFileName) {
-            InternalMove(sourceFileName, destFileName);
-        }
-
-        private static void InternalMove(String sourceFileName, String destFileName) {
-            if (sourceFileName == null)
-                throw new ArgumentNullException(nameof(sourceFileName), Environment.GetResourceString("ArgumentNull_FileName"));
-            if (destFileName == null)
-                throw new ArgumentNullException(nameof(destFileName), Environment.GetResourceString("ArgumentNull_FileName"));
-            if (sourceFileName.Length == 0)
-                throw new ArgumentException(Environment.GetResourceString("Argument_EmptyFileName"), nameof(sourceFileName));
-            if (destFileName.Length == 0)
-                throw new ArgumentException(Environment.GetResourceString("Argument_EmptyFileName"), nameof(destFileName));
-            Contract.EndContractBlock();
-            
-            String fullSourceFileName = Path.GetFullPath(sourceFileName);
-            String fullDestFileName = Path.GetFullPath(destFileName);
-
-            if (!InternalExists(fullSourceFileName))
-                __Error.WinIOError(Win32Native.ERROR_FILE_NOT_FOUND, fullSourceFileName);
-            
-            if (!Win32Native.MoveFile(fullSourceFileName, fullDestFileName))
-            {
-                __Error.WinIOError();
-            }
-        }
-
-
-        public static void Replace(String sourceFileName, String destinationFileName, String destinationBackupFileName)
-        {
-            if (sourceFileName == null)
-                throw new ArgumentNullException(nameof(sourceFileName));
-            if (destinationFileName == null)
-                throw new ArgumentNullException(nameof(destinationFileName));
-            Contract.EndContractBlock();
-
-            InternalReplace(sourceFileName, destinationFileName, destinationBackupFileName, false);
-        }
-
-        public static void Replace(String sourceFileName, String destinationFileName, String destinationBackupFileName, bool ignoreMetadataErrors)
-        {
-            if (sourceFileName == null)
-                throw new ArgumentNullException(nameof(sourceFileName));
-            if (destinationFileName == null)
-                throw new ArgumentNullException(nameof(destinationFileName));
-            Contract.EndContractBlock();
-
-            InternalReplace(sourceFileName, destinationFileName, destinationBackupFileName, ignoreMetadataErrors);
-        }
-
-        private static void InternalReplace(String sourceFileName, String destinationFileName, String destinationBackupFileName, bool ignoreMetadataErrors)
-        {
-            Contract.Requires(sourceFileName != null);
-            Contract.Requires(destinationFileName != null);
-
-            String fullSrcPath = Path.GetFullPath(sourceFileName);
-            String fullDestPath = Path.GetFullPath(destinationFileName);
-            String fullBackupPath = null;
-            if (destinationBackupFileName != null)
-                fullBackupPath = Path.GetFullPath(destinationBackupFileName);
-
-            int flags = Win32Native.REPLACEFILE_WRITE_THROUGH;
-            if (ignoreMetadataErrors)
-                flags |= Win32Native.REPLACEFILE_IGNORE_MERGE_ERRORS;
-
-            bool r = Win32Native.ReplaceFile(fullDestPath, fullSrcPath, fullBackupPath, flags, IntPtr.Zero, IntPtr.Zero);
-            if (!r)
-                __Error.WinIOError();
-        }
-
-
+#endif // PLATFORM_UNIX
+        
         // Returns 0 on success, otherwise a Win32 error code.  Note that
         // classes should use -1 as the uninitialized state for dataInitialized.
         internal static int FillAttributeInfo(String path, ref Win32Native.WIN32_FILE_ATTRIBUTE_DATA data, bool tryagain, bool returnErrorOnNotFound)
diff --git a/src/mscorlib/src/System/IO/FileAccess.cs b/src/mscorlib/src/System/IO/FileAccess.cs
index f708a284c1..707b58f78b 100644
--- a/src/mscorlib/src/System/IO/FileAccess.cs
+++ b/src/mscorlib/src/System/IO/FileAccess.cs
@@ -23,7 +23,6 @@ namespace System.IO {
     // 
 [Serializable]
 [Flags]
-[System.Runtime.InteropServices.ComVisible(true)]
     public enum FileAccess
     {
         // Specifies read access to the file. Data can be read from the file and
diff --git a/src/mscorlib/src/System/IO/FileAttributes.cs b/src/mscorlib/src/System/IO/FileAttributes.cs
deleted file mode 100644
index 51ef597f9d..0000000000
--- a/src/mscorlib/src/System/IO/FileAttributes.cs
+++ /dev/null
@@ -1,39 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-// See the LICENSE file in the project root for more information.
-
-/*============================================================
-**
-** 
-** Purpose: File attribute flags corresponding to NT's flags.
-**
-** 
-===========================================================*/
-using System;
-
-namespace System.IO
-{
-    // File attributes for use with the FileEnumerator class.
-    // These constants correspond to the constants in WinNT.h.
-    [Serializable]
-    [Flags]
-    [System.Runtime.InteropServices.ComVisible(true)]
-    public enum FileAttributes
-    {
-        // From WinNT.h (FILE_ATTRIBUTE_XXX)
-        ReadOnly = 0x1,
-        Hidden = 0x2,
-        System = 0x4,
-        Directory = 0x10,
-        Archive = 0x20,
-        Device = 0x40,
-        Normal = 0x80,
-        Temporary = 0x100,
-        SparseFile = 0x200,
-        ReparsePoint = 0x400,
-        Compressed = 0x800,
-        Offline = 0x1000,
-        NotContentIndexed = 0x2000,
-        Encrypted = 0x4000,
-    }
-}
diff --git a/src/mscorlib/src/System/IO/FileInfo.cs b/src/mscorlib/src/System/IO/FileInfo.cs
deleted file mode 100644
index 32622c63a1..0000000000
--- a/src/mscorlib/src/System/IO/FileInfo.cs
+++ /dev/null
@@ -1,270 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-// See the LICENSE file in the project root for more information.
-
-using Win32Native = Microsoft.Win32.Win32Native;
-using System.Runtime.InteropServices;
-using System.Text;
-using System.Runtime.Serialization;
-using System.Globalization;
-using System.Runtime.Versioning;
-using System.Diagnostics;
-using System.Diagnostics.Contracts;
-
-namespace System.IO
-{
-    // Class for creating FileStream objects, and some basic file management
-    // routines such as Delete, etc.
-    [Serializable]
-    [ComVisible(true)]
-    public sealed class FileInfo: FileSystemInfo
-    {
-        private String _name;
-
-        // Migrating InheritanceDemands requires this default ctor, so we can annotate it.
-        private FileInfo(){}
-
-        public FileInfo(String fileName)
-        {
-            if (fileName == null)
-                throw new ArgumentNullException(nameof(fileName));
-            Contract.EndContractBlock();
-
-            Init(fileName);
-        }
-
-        private void Init(String fileName)
-        {
-            OriginalPath = fileName;
-            _name = Path.GetFileName(fileName);
-            FullPath = Path.GetFullPath(fileName);
-            DisplayPath = GetDisplayPath(fileName);
-        }
-
-        private String GetDisplayPath(String originalPath)
-        {
-            return Path.GetFileName(originalPath);
-        }
-
-        private FileInfo(SerializationInfo info, StreamingContext context) : base(info, context)
-        {
-            _name = Path.GetFileName(OriginalPath);
-            DisplayPath = GetDisplayPath(OriginalPath);
-        }
-
-        internal FileInfo(String fullPath, bool ignoreThis)
-        {
-            Debug.Assert(PathInternal.GetRootLength(fullPath) > 0, "fullPath must be fully qualified!");
-            _name = Path.GetFileName(fullPath);
-            OriginalPath = _name;
-            FullPath = fullPath;
-            DisplayPath = _name;
-        }
-
-        public override String Name {
-            get { return _name; }
-        }
-
-        public long Length {
-            get {
-                if (_dataInitialised == -1)
-                    Refresh();
-                
-                if (_dataInitialised != 0) // Refresh was unable to initialise the data
-                    __Error.WinIOError(_dataInitialised, DisplayPath);
-        
-                if ((_data.fileAttributes & Win32Native.FILE_ATTRIBUTE_DIRECTORY) != 0)
-                    __Error.WinIOError(Win32Native.ERROR_FILE_NOT_FOUND, DisplayPath);
-                
-                return ((long)_data.fileSizeHigh) << 32 | ((long)_data.fileSizeLow & 0xFFFFFFFFL);
-            }
-        }
-
-        /* Returns the name of the directory that the file is in */
-        public String DirectoryName
-        {
-            get
-            {
-                return Path.GetDirectoryName(FullPath);
-            }
-        }
-
-        /* Creates an instance of the the parent directory */
-        public DirectoryInfo Directory
-        {
-            get
-            {
-                String dirName = DirectoryName;
-                if (dirName == null)
-                    return null;
-                return new DirectoryInfo(dirName);
-            }
-        } 
-
-        public bool IsReadOnly {
-            get {
-                return (Attributes & FileAttributes.ReadOnly) != 0;
-            }
-            set {
-                if (value)
-                    Attributes |= FileAttributes.ReadOnly;
-                else
-                    Attributes &= ~FileAttributes.ReadOnly;
-            }
-        }
-
-        public StreamReader OpenText()
-        {
-            return new StreamReader(FullPath, Encoding.UTF8, true, StreamReader.DefaultBufferSize);
-        }
-
-        public StreamWriter CreateText()
-        {
-            return new StreamWriter(FullPath,false);
-        }
-
-        public StreamWriter AppendText()
-        {
-            return new StreamWriter(FullPath,true);
-        }
-
-        // Copies an existing file to a new file. An exception is raised if the
-        // destination file already exists. Use the 
-        // Copy(String, String, boolean) method to allow 
-        // overwriting an existing file.
-        public FileInfo CopyTo(String destFileName) {
-            if (destFileName == null)
-                throw new ArgumentNullException(nameof(destFileName), Environment.GetResourceString("ArgumentNull_FileName"));
-            if (destFileName.Length == 0)
-                throw new ArgumentException(Environment.GetResourceString("Argument_EmptyFileName"), nameof(destFileName));
-            Contract.EndContractBlock();
-
-            destFileName = File.InternalCopy(FullPath, destFileName, false);
-            return new FileInfo(destFileName, false);
-        }
-
-        // Copies an existing file to a new file. If overwrite is 
-        // false, then an IOException is thrown if the destination file 
-        // already exists.  If overwrite is true, the file is 
-        // overwritten.
-        public FileInfo CopyTo(String destFileName, bool overwrite) {
-            if (destFileName == null)
-                throw new ArgumentNullException(nameof(destFileName), Environment.GetResourceString("ArgumentNull_FileName"));
-            if (destFileName.Length == 0)
-                throw new ArgumentException(Environment.GetResourceString("Argument_EmptyFileName"), nameof(destFileName));
-            Contract.EndContractBlock();
-
-            destFileName = File.InternalCopy(FullPath, destFileName, overwrite);
-            return new FileInfo(destFileName, false);
-        }
-
-        public FileStream Create() {
-            return File.Create(FullPath);
-        }
-
-        // Deletes a file. The file specified by the designated path is deleted. 
-        // If the file does not exist, Delete succeeds without throwing
-        // an exception.
-        // 
-        // On NT, Delete will fail for a file that is open for normal I/O
-        // or a file that is memory mapped.
-        public override void Delete()
-        {
-            bool r = Win32Native.DeleteFile(FullPath);
-            if (!r) {
-                int hr = Marshal.GetLastWin32Error();
-                if (hr==Win32Native.ERROR_FILE_NOT_FOUND)
-                    return;
-                else
-                    __Error.WinIOError(hr, DisplayPath);
-            }
-        }
-
-        // Tests if the given file exists. The result is true if the file
-        // given by the specified path exists; otherwise, the result is
-        // false.  
-        public override bool Exists {
-            get {
-                try {
-                    if (_dataInitialised == -1)
-                        Refresh();
-                    if (_dataInitialised != 0) {
-                        // Refresh was unable to initialise the data.
-                        // We should normally be throwing an exception here, 
-                        // but Exists is supposed to return true or false.
-                        return false;
-                    }
-                    return (_data.fileAttributes & Win32Native.FILE_ATTRIBUTE_DIRECTORY) == 0;
-                }
-                catch
-                {
-                    return false;
-                }
-            }
-        }
-
-        // User must explicitly specify opening a new file or appending to one.
-        public FileStream Open(FileMode mode) {
-            return Open(mode, FileAccess.ReadWrite, FileShare.None);
-        }
-
-        public FileStream Open(FileMode mode, FileAccess access) {
-            return Open(mode, access, FileShare.None);
-        }
-
-        public FileStream Open(FileMode mode, FileAccess access, FileShare share) {
-            return new FileStream(FullPath, mode, access, share);
-        }
-
-        public FileStream OpenRead()
-        {
-            return new FileStream(FullPath, FileMode.Open, FileAccess.Read,
-                                  FileShare.Read, 4096, false);
-        }
-
-        public FileStream OpenWrite() {
-            return new FileStream(FullPath, FileMode.OpenOrCreate, 
-                                  FileAccess.Write, FileShare.None);
-        }
-
-        // Moves a given file to a new location and potentially a new file name.
-        // This method does work across volumes.
-        public void MoveTo(String destFileName) {
-            if (destFileName==null)
-                throw new ArgumentNullException(nameof(destFileName));
-            if (destFileName.Length==0)
-                throw new ArgumentException(Environment.GetResourceString("Argument_EmptyFileName"), nameof(destFileName));
-            Contract.EndContractBlock();
-
-            string fullDestFileName = Path.GetFullPath(destFileName);
-
-            if (!Win32Native.MoveFile(FullPath, fullDestFileName))
-                __Error.WinIOError();
-            FullPath = fullDestFileName;
-            OriginalPath = destFileName;
-            _name = Path.GetFileName(fullDestFileName);
-            DisplayPath = GetDisplayPath(destFileName);
-            // Flush any cached information about the file.
-            _dataInitialised = -1;
-        }
-
-        [ComVisible(false)]
-        public FileInfo Replace(String destinationFileName, String destinationBackupFileName)
-        {
-            return Replace(destinationFileName, destinationBackupFileName, false);
-        }
-
-        [ComVisible(false)]
-        public FileInfo Replace(String destinationFileName, String destinationBackupFileName, bool ignoreMetadataErrors)
-        {
-            File.Replace(FullPath, destinationFileName, destinationBackupFileName, ignoreMetadataErrors);
-            return new FileInfo(destinationFileName);
-        }
-
-        // Returns the display path
-        public override String ToString()
-        {
-            return DisplayPath;
-        }
-    }
-}
diff --git a/src/mscorlib/src/System/IO/FileLoadException.cs b/src/mscorlib/src/System/IO/FileLoadException.cs
index 2b56c00191..980d2514aa 100644
--- a/src/mscorlib/src/System/IO/FileLoadException.cs
+++ b/src/mscorlib/src/System/IO/FileLoadException.cs
@@ -20,14 +20,12 @@ using System.Runtime.Serialization;
 using System.Runtime.InteropServices;
 using System.Runtime.CompilerServices;
 using System.Security;
-using System.Security.Permissions;
 using System.Runtime.Versioning;
 using SecurityException = System.Security.SecurityException;
 
 namespace System.IO {
 
     [Serializable]
-    [System.Runtime.InteropServices.ComVisible(true)]
     public class FileLoadException : IOException {
 
         private String _fileName;   // the name of the file we could not load.
diff --git a/src/mscorlib/src/System/IO/FileMode.cs b/src/mscorlib/src/System/IO/FileMode.cs
index 9b9c2024a7..3972cf0533 100644
--- a/src/mscorlib/src/System/IO/FileMode.cs
+++ b/src/mscorlib/src/System/IO/FileMode.cs
@@ -27,7 +27,6 @@ namespace System.IO {
     // exist, use Create.
     // 
     [Serializable]
-[System.Runtime.InteropServices.ComVisible(true)]
     public enum FileMode
     {
         // Creates a new file. An exception is raised if the file already exists.
diff --git a/src/mscorlib/src/System/IO/FileNotFoundException.cs b/src/mscorlib/src/System/IO/FileNotFoundException.cs
index 8cc75f8232..ad6b5386ba 100644
--- a/src/mscorlib/src/System/IO/FileNotFoundException.cs
+++ b/src/mscorlib/src/System/IO/FileNotFoundException.cs
@@ -16,14 +16,12 @@
 
 using System;
 using System.Runtime.Serialization;
-using System.Security.Permissions;
 using SecurityException = System.Security.SecurityException;
 using System.Globalization;
 
 namespace System.IO {
     // Thrown when trying to access a file that doesn't exist on disk.
     [Serializable]
-    [System.Runtime.InteropServices.ComVisible(true)]
     public class FileNotFoundException : IOException {
 
         private String _fileName;  // The name of the file that isn't found.
diff --git a/src/mscorlib/src/System/IO/FileOptions.cs b/src/mscorlib/src/System/IO/FileOptions.cs
index ffd6ddad90..02bc99eea4 100644
--- a/src/mscorlib/src/System/IO/FileOptions.cs
+++ b/src/mscorlib/src/System/IO/FileOptions.cs
@@ -24,7 +24,6 @@ namespace System.IO {
     // a number of them made sense in managed code, at least not yet.
     [Serializable]
     [Flags]
-    [ComVisible(true)]
     public enum FileOptions
     {
         // NOTE: any change to FileOptions enum needs to be 
diff --git a/src/mscorlib/src/System/IO/FileShare.cs b/src/mscorlib/src/System/IO/FileShare.cs
index ad76d5da09..8a7d1f05e9 100644
--- a/src/mscorlib/src/System/IO/FileShare.cs
+++ b/src/mscorlib/src/System/IO/FileShare.cs
@@ -28,7 +28,6 @@ namespace System.IO {
     // 
 [Serializable]
 [Flags]
-[System.Runtime.InteropServices.ComVisible(true)]
     public enum FileShare
     {
         // No sharing. Any request to open the file (by this process or another
diff --git a/src/mscorlib/src/System/IO/FileSystemEnumerable.cs b/src/mscorlib/src/System/IO/FileSystemEnumerable.cs
index f861805ccf..0316de0f93 100644
--- a/src/mscorlib/src/System/IO/FileSystemEnumerable.cs
+++ b/src/mscorlib/src/System/IO/FileSystemEnumerable.cs
@@ -25,7 +25,6 @@ using System.Threading;
 
 namespace System.IO
 {
-
     // Overview:
     // The key methods instantiate FileSystemEnumerableIterators. These compose the iterator with search result
     // handlers that instantiate the FileInfo, DirectoryInfo, String, etc. The handlers then perform any
@@ -42,37 +41,6 @@ namespace System.IO
             SearchResultHandler<String> handler = new StringResultHandler(includeFiles, includeDirs);
             return new FileSystemEnumerableIterator<String>(path, originalUserPath, searchPattern, searchOption, handler, checkHost);
         }
-
-        internal static IEnumerable<FileInfo> CreateFileInfoIterator(String path, String originalUserPath, String searchPattern, SearchOption searchOption)
-        {
-            Contract.Requires(path != null);
-            Contract.Requires(originalUserPath != null);
-            Contract.Requires(searchPattern != null);
-
-            SearchResultHandler<FileInfo> handler = new FileInfoResultHandler();
-            return new FileSystemEnumerableIterator<FileInfo>(path, originalUserPath, searchPattern, searchOption, handler, true);
-        }
-
-        internal static IEnumerable<DirectoryInfo> CreateDirectoryInfoIterator(String path, String originalUserPath, String searchPattern, SearchOption searchOption)
-        {
-
-            Contract.Requires(path != null);
-            Contract.Requires(originalUserPath != null);
-            Contract.Requires(searchPattern != null);
-
-            SearchResultHandler<DirectoryInfo> handler = new DirectoryInfoResultHandler();
-            return new FileSystemEnumerableIterator<DirectoryInfo>(path, originalUserPath, searchPattern, searchOption, handler, true);
-        }
-
-        internal static IEnumerable<FileSystemInfo> CreateFileSystemInfoIterator(String path, String originalUserPath, String searchPattern, SearchOption searchOption)
-        {
-            Contract.Requires(path != null);
-            Contract.Requires(originalUserPath != null);
-            Contract.Requires(searchPattern != null);
-
-            SearchResultHandler<FileSystemInfo> handler = new FileSystemInfoResultHandler();
-            return new FileSystemEnumerableIterator<FileSystemInfo>(path, originalUserPath, searchPattern, searchOption, handler, true);
-        }
     }
 
     // Abstract Iterator, borrowed from Linq. Used in anticipation of need for similar enumerables
@@ -166,11 +134,11 @@ namespace System.IO
         private String searchCriteria;
         SafeFindHandle _hnd = null;
 
-        // empty means we know in advance that we won’t find any search results, which can happen if:
-        // 1. we don’t have a search pattern
-        // 2. we’re enumerating only the top directory and found no matches during the first call
-        // This flag allows us to return early for these cases. We can’t know this in advance for
-        // SearchOption.AllDirectories because we do a “*” search for subdirs and then use the
+        // empty means we know in advance that we won't find any search results, which can happen if:
+        // 1. we don't have a search pattern
+        // 2. we're enumerating only the top directory and found no matches during the first call
+        // This flag allows us to return early for these cases. We can't know this in advance for
+        // SearchOption.AllDirectories because we do a "*" search for subdirs and then use the
         // searchPattern at each directory level.
         bool empty;
 
@@ -603,71 +571,6 @@ namespace System.IO
         }
     }
 
-    internal class FileInfoResultHandler : SearchResultHandler<FileInfo>
-    {
-        internal override bool IsResultIncluded(SearchResult result)
-        {
-            return FileSystemEnumerableHelpers.IsFile(result.FindData);
-        }
-
-        internal override FileInfo CreateObject(SearchResult result)
-        {
-            String name = result.FullPath;
-            FileInfo fi = new FileInfo(name, false);
-            fi.InitializeFrom(result.FindData);
-            return fi;
-        }
-    }
-
-    internal class DirectoryInfoResultHandler : SearchResultHandler<DirectoryInfo>
-    {
-        internal override bool IsResultIncluded(SearchResult result)
-        {
-            return FileSystemEnumerableHelpers.IsDir(result.FindData);
-        }
-
-        internal override DirectoryInfo CreateObject(SearchResult result)
-        {
-            DirectoryInfo di = new DirectoryInfo(result.FullPath, false);
-            di.InitializeFrom(result.FindData);
-            return di;
-        }
-    }
-
-    internal class FileSystemInfoResultHandler : SearchResultHandler<FileSystemInfo>
-    {
-
-        internal override bool IsResultIncluded(SearchResult result)
-        {
-            bool includeFile = FileSystemEnumerableHelpers.IsFile(result.FindData);
-            bool includeDir = FileSystemEnumerableHelpers.IsDir(result.FindData);
-            Debug.Assert(!(includeFile && includeDir), result.FindData.cFileName + ": current item can't be both file and dir!");
-
-            return (includeDir || includeFile);
-        }
-
-        internal override FileSystemInfo CreateObject(SearchResult result)
-        {
-            bool isFile = FileSystemEnumerableHelpers.IsFile(result.FindData);
-            bool isDir = FileSystemEnumerableHelpers.IsDir(result.FindData);
-
-            if (isDir)
-            {
-                DirectoryInfo di = new DirectoryInfo(result.FullPath, false);
-                di.InitializeFrom(result.FindData);
-                return di;
-            }
-            else
-            {
-                Contract.Assert(isFile);
-                FileInfo fi = new FileInfo(result.FullPath, false);
-                fi.InitializeFrom(result.FindData);
-                return fi;
-            }
-        }
-
-    }
-
     internal sealed class SearchResult
     {
         private String fullPath;     // fully-qualifed path
diff --git a/src/mscorlib/src/System/IO/FileSystemInfo.cs b/src/mscorlib/src/System/IO/FileSystemInfo.cs
deleted file mode 100644
index 94cd531b07..0000000000
--- a/src/mscorlib/src/System/IO/FileSystemInfo.cs
+++ /dev/null
@@ -1,240 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-// See the LICENSE file in the project root for more information.
-
-using Microsoft.Win32;
-using System.Runtime.InteropServices;
-using System.Runtime.Serialization;
-using System.Diagnostics.Contracts;
-
-namespace System.IO
-{
-#if FEATURE_SERIALIZATION
-    [Serializable]
-#endif
-    [ComVisible(true)]
-    public abstract class FileSystemInfo : MarshalByRefObject, ISerializable {
-        
-        internal Win32Native.WIN32_FILE_ATTRIBUTE_DATA _data; // Cache the file information
-        internal int _dataInitialised = -1; // We use this field in conjunction with the Refresh methods, if we succeed
-                                            // we store a zero, on failure we store the HResult in it so that we can
-                                            // give back a generic error back.
-
-        private const int ERROR_INVALID_PARAMETER = 87;
-        internal const int ERROR_ACCESS_DENIED = 0x5;
-
-        protected String FullPath;          // fully qualified path of the directory
-        protected String OriginalPath;      // path passed in by the user
-        private String _displayPath = "";   // path that can be displayed to the user
-
-        protected FileSystemInfo()
-        {
-        }
-
-        protected FileSystemInfo(SerializationInfo info, StreamingContext context)
-        {
-            if (info == null)
-                throw new ArgumentNullException(nameof(info));
-            Contract.EndContractBlock();
-
-            // Must use V1 field names here, since V1 didn't implement 
-            // ISerializable.
-            FullPath = Path.GetFullPath(info.GetString("FullPath"));
-            OriginalPath = info.GetString("OriginalPath");
-
-            // Lazily initialize the file attributes.
-            _dataInitialised = -1;
-        }
-
-        internal void InitializeFrom(Win32Native.WIN32_FIND_DATA findData)
-        {
-            _data = new Win32Native.WIN32_FILE_ATTRIBUTE_DATA();
-            _data.PopulateFrom(findData);
-            _dataInitialised = 0;
-        }
-
-        // Full path of the direcory/file
-        public virtual String FullName {
-            get 
-            {
-                return FullPath;
-            }
-        }
-
-        public String Extension 
-        {
-            get
-            {
-                // GetFullPathInternal would have already stripped out the terminating "." if present.
-               int length = FullPath.Length;
-                for (int i = length; --i >= 0;) {
-                    char ch = FullPath[i];
-                    if (ch == '.')
-                        return FullPath.Substring(i, length - i);
-                    if (ch == Path.DirectorySeparatorChar || ch == Path.AltDirectorySeparatorChar || ch == Path.VolumeSeparatorChar)
-                        break;
-                }
-                return String.Empty;
-            }
-        }
-
-        // For files name of the file is returned, for directories the last directory in hierarchy is returned if possible,
-        // otherwise the fully qualified name s returned
-        public abstract String Name {
-            get;
-        }
-        
-        // Whether a file/directory exists
-        public abstract bool Exists
-        {
-            get;
-        }
-
-        // Delete a file/directory
-        public abstract void Delete();
-
-        public DateTime CreationTime
-        {
-            get {
-                    // depends on the security check in get_CreationTimeUtc
-                    return CreationTimeUtc.ToLocalTime();
-            }
-        }
-
-       [ComVisible(false)]
-       public DateTime CreationTimeUtc {
-            get {
-                if (_dataInitialised == -1) {
-                    _data = new Win32Native.WIN32_FILE_ATTRIBUTE_DATA();
-                    Refresh();
-                }
-
-                if (_dataInitialised != 0) // Refresh was unable to initialise the data
-                    __Error.WinIOError(_dataInitialised, DisplayPath);
-                
-                long fileTime = ((long)_data.ftCreationTimeHigh << 32) | _data.ftCreationTimeLow;
-                return DateTime.FromFileTimeUtc(fileTime);
-                
-            }
-        }
-
-        public DateTime LastAccessTime
-        {
-           get {
-                // depends on the security check in get_LastAccessTimeUtc
-                return LastAccessTimeUtc.ToLocalTime();
-           }
-           set {
-                LastAccessTimeUtc = value.ToUniversalTime();
-            }
-        }
-
-        [ComVisible(false)]
-        public DateTime LastAccessTimeUtc {
-            get {
-                if (_dataInitialised == -1) {
-                    _data = new Win32Native.WIN32_FILE_ATTRIBUTE_DATA();
-                    Refresh();
-                }
-
-                if (_dataInitialised != 0) // Refresh was unable to initialise the data
-                    __Error.WinIOError(_dataInitialised, DisplayPath);
-                    
-                long fileTime = ((long)_data.ftLastAccessTimeHigh << 32) | _data.ftLastAccessTimeLow;
-                return DateTime.FromFileTimeUtc(fileTime);
-            }
-
-            set {
-            }
-        }
-
-        public DateTime LastWriteTime
-        {
-            get {
-                // depends on the security check in get_LastWriteTimeUtc
-                return LastWriteTimeUtc.ToLocalTime();
-            }
-
-            set {
-                LastWriteTimeUtc = value.ToUniversalTime();
-            }
-        }
-
-        [ComVisible(false)]
-        public DateTime LastWriteTimeUtc {
-            get {
-                if (_dataInitialised == -1) {
-                    _data = new Win32Native.WIN32_FILE_ATTRIBUTE_DATA();
-                    Refresh();
-                }
-
-                if (_dataInitialised != 0) // Refresh was unable to initialise the data
-                    __Error.WinIOError(_dataInitialised, DisplayPath);
-        
-            
-                long fileTime = ((long)_data.ftLastWriteTimeHigh << 32) | _data.ftLastWriteTimeLow;
-                return DateTime.FromFileTimeUtc(fileTime);
-            }
-
-            set {
-            }
-        }
-
-        public void Refresh()
-        {
-            _dataInitialised = File.FillAttributeInfo(FullPath, ref _data, false, false);
-        }
-
-        public FileAttributes Attributes {
-            get
-            {
-                if (_dataInitialised == -1) {
-                    _data = new Win32Native.WIN32_FILE_ATTRIBUTE_DATA();
-                    Refresh(); // Call refresh to intialise the data
-                }
-
-                if (_dataInitialised != 0) // Refresh was unable to initialise the data
-                    __Error.WinIOError(_dataInitialised, DisplayPath);
-
-                return (FileAttributes) _data.fileAttributes;
-            }
-
-            set {
-                bool r = Win32Native.SetFileAttributes(FullPath, (int) value);
-                if (!r) {
-                    int hr = Marshal.GetLastWin32Error();
-                    
-                    if (hr==ERROR_INVALID_PARAMETER)
-                        throw new ArgumentException(Environment.GetResourceString("Arg_InvalidFileAttrs"));
-                    
-                    // For whatever reason we are turning ERROR_ACCESS_DENIED into 
-                    // ArgumentException here (probably done for some 9x code path).
-                    // We can't change this now but special casing the error message instead.
-                    if (hr == ERROR_ACCESS_DENIED)
-                        throw new ArgumentException(Environment.GetResourceString("UnauthorizedAccess_IODenied_NoPathName"));
-                    __Error.WinIOError(hr, DisplayPath);
-                }
-                _dataInitialised = -1;
-            }
-        }
-
-        [ComVisible(false)]
-        public virtual void GetObjectData(SerializationInfo info, StreamingContext context)
-        {
-            info.AddValue("OriginalPath", OriginalPath, typeof(String));
-            info.AddValue("FullPath", FullPath, typeof(String));
-        }
-
-        internal String DisplayPath
-        {
-            get
-            {
-                return _displayPath;
-            }
-            set
-            {
-                _displayPath = value;
-            }
-        }
-    }
-}
diff --git a/src/mscorlib/src/System/IO/IOException.cs b/src/mscorlib/src/System/IO/IOException.cs
index b3db033b0d..ab612811b0 100644
--- a/src/mscorlib/src/System/IO/IOException.cs
+++ b/src/mscorlib/src/System/IO/IOException.cs
@@ -19,7 +19,6 @@ using System.Runtime.Serialization;
 namespace System.IO {
 
     [Serializable]
-    [System.Runtime.InteropServices.ComVisible(true)]
     public class IOException : SystemException
     {
         // For debugging purposes, store the complete path in the IOException
diff --git a/src/mscorlib/src/System/IO/MemoryStream.cs b/src/mscorlib/src/System/IO/MemoryStream.cs
index bdddc83818..05aac909b5 100644
--- a/src/mscorlib/src/System/IO/MemoryStream.cs
+++ b/src/mscorlib/src/System/IO/MemoryStream.cs
@@ -23,7 +23,6 @@ using System.Diagnostics;
 using System.Diagnostics.Contracts;
 using System.Threading;
 using System.Threading.Tasks;
-using System.Security.Permissions;
 
 namespace System.IO {
     // A MemoryStream represents a Stream in memory (ie, it has no backing store).
@@ -35,7 +34,6 @@ namespace System.IO {
     // memory streams are resizable, while ones created with a byte array provide
     // a stream "view" of the data.
     [Serializable]
-    [ComVisible(true)]
     public class MemoryStream : Stream
     {
         private byte[] _buffer;    // Either allocated internally or externally.
@@ -181,7 +179,6 @@ namespace System.IO {
         public override void Flush() {
         }
 
-        [ComVisible(false)]
         public override Task FlushAsync(CancellationToken cancellationToken) {
 
             if (cancellationToken.IsCancellationRequested)
@@ -357,7 +354,6 @@ namespace System.IO {
             return n;
         }
 
-        [ComVisible(false)]
         public override Task<int> ReadAsync(Byte[] buffer, int offset, int count, CancellationToken cancellationToken)
         {
             if (buffer==null)
@@ -589,7 +585,6 @@ namespace System.IO {
 
         }
 
-        [ComVisible(false)]
         public override Task WriteAsync(Byte[] buffer, int offset, int count, CancellationToken cancellationToken)
         {
             if (buffer == null)
diff --git a/src/mscorlib/src/System/IO/PathTooLongException.cs b/src/mscorlib/src/System/IO/PathTooLongException.cs
index b1063232a1..a84fdfbb36 100644
--- a/src/mscorlib/src/System/IO/PathTooLongException.cs
+++ b/src/mscorlib/src/System/IO/PathTooLongException.cs
@@ -20,7 +20,6 @@ using System.Runtime.Serialization;
 namespace System.IO {
 
     [Serializable]
-    [System.Runtime.InteropServices.ComVisible(true)]
     public class PathTooLongException : IOException
     {
         public PathTooLongException() 
diff --git a/src/mscorlib/src/System/IO/PinnedBufferMemoryStream.cs b/src/mscorlib/src/System/IO/PinnedBufferMemoryStream.cs
index 890669fa58..2cbd14f734 100644
--- a/src/mscorlib/src/System/IO/PinnedBufferMemoryStream.cs
+++ b/src/mscorlib/src/System/IO/PinnedBufferMemoryStream.cs
@@ -42,8 +42,8 @@ namespace System.IO {
             _pinningHandle = new GCHandle(array, GCHandleType.Pinned);
             // Now the byte[] is pinned for the lifetime of this instance.
             // But I also need to get a pointer to that block of memory...
-            fixed(byte* ptr = _array)
-                Initialize(ptr, len, len, FileAccess.Read, true);
+            fixed(byte* ptr = &_array[0])
+                Initialize(ptr, len, len, FileAccess.Read);
         }
 
         ~PinnedBufferMemoryStream()
diff --git a/src/mscorlib/src/System/IO/ReadLinesIterator.cs b/src/mscorlib/src/System/IO/ReadLinesIterator.cs
deleted file mode 100644
index ce2ad2ad0f..0000000000
--- a/src/mscorlib/src/System/IO/ReadLinesIterator.cs
+++ /dev/null
@@ -1,102 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-// See the LICENSE file in the project root for more information.
-using System;
-using System.Diagnostics.Contracts;
-using System.Runtime.Versioning;
-using System.Text;
-
-namespace System.IO
-{
-    // An iterator that returns a single line at-a-time from a given file.
-    //
-    // Known issues which cannot be changed to remain compatible with 4.0:
-    //
-    //  - The underlying StreamReader is allocated upfront for the IEnumerable<T> before 
-    //    GetEnumerator has even been called. While this is good in that exceptions such as 
-    //    DirectoryNotFoundException and FileNotFoundException are thrown directly by 
-    //    File.ReadLines (which the user probably expects), it also means that the reader 
-    //    will be leaked if the user never actually foreach's over the enumerable (and hence 
-    //    calls Dispose on at least one IEnumerator<T> instance).
-    //
-    //  - Reading to the end of the IEnumerator<T> disposes it. This means that Dispose 
-    //    is called twice in a normal foreach construct.
-    //
-    //  - IEnumerator<T> instances from the same IEnumerable<T> party on the same underlying 
-    //    reader (Dev10 Bugs 904764).
-    //
-    internal class ReadLinesIterator : Iterator<string>
-    {
-        private readonly string _path;
-        private readonly Encoding _encoding;
-        private StreamReader _reader;
-
-        private ReadLinesIterator(string path, Encoding encoding, StreamReader reader)
-        {
-            Contract.Requires(path != null);
-            Contract.Requires(path.Length > 0);
-            Contract.Requires(encoding != null);
-            Contract.Requires(reader != null);
-
-            _path = path;
-            _encoding = encoding;
-            _reader = reader;
-        }
-
-        public override bool MoveNext()
-        {
-            if (this._reader != null)
-            {
-                this.current = _reader.ReadLine();
-                if (this.current != null)
-                    return true;
-
-                // To maintain 4.0 behavior we Dispose 
-                // after reading to the end of the reader.
-                Dispose();
-            }
-
-            return false;
-        }
-
-        protected override Iterator<string> Clone()
-        {
-            // NOTE: To maintain the same behavior with the previous yield-based
-            // iterator in 4.0, we have all the IEnumerator<T> instances share the same 
-            // underlying reader. If we have already been disposed, _reader will be null, 
-            // which will cause CreateIterator to simply new up a new instance to start up
-            // a new iteration. Dev10 Bugs 904764 has been filed to fix this in next side-
-            // by-side release.
-            return CreateIterator(_path, _encoding, _reader);
-        }
-
-        protected override void Dispose(bool disposing)
-        {
-            try
-            {
-                if (disposing)
-                {
-                    if (_reader != null)
-                    {
-                        _reader.Dispose();
-                    }
-                }
-            }
-            finally
-            {
-                _reader = null;
-                base.Dispose(disposing);
-            }
-        }
-
-        internal static ReadLinesIterator CreateIterator(string path, Encoding encoding)
-        {
-            return CreateIterator(path, encoding, (StreamReader)null);
-        }
-
-        private static ReadLinesIterator CreateIterator(string path, Encoding encoding, StreamReader reader)
-        {
-            return new ReadLinesIterator(path, encoding, reader ?? new StreamReader(path, encoding));
-        }
-    }
-}
diff --git a/src/mscorlib/src/System/IO/SearchOption.cs b/src/mscorlib/src/System/IO/SearchOption.cs
index aa9b9e37f8..e2f761cd54 100644
--- a/src/mscorlib/src/System/IO/SearchOption.cs
+++ b/src/mscorlib/src/System/IO/SearchOption.cs
@@ -20,7 +20,6 @@ using System;
 
 namespace System.IO {
     [Serializable]
-[System.Runtime.InteropServices.ComVisible(true)]
     public enum SearchOption
     {
         // Include only the current directory in the search operation
diff --git a/src/mscorlib/src/System/IO/SeekOrigin.cs b/src/mscorlib/src/System/IO/SeekOrigin.cs
index a0a013e7aa..bff49e610f 100644
--- a/src/mscorlib/src/System/IO/SeekOrigin.cs
+++ b/src/mscorlib/src/System/IO/SeekOrigin.cs
@@ -21,7 +21,6 @@ namespace System.IO {
     // Provides seek reference points.  To seek to the end of a stream,
     // call stream.Seek(0, SeekOrigin.End).
     [Serializable]
-    [System.Runtime.InteropServices.ComVisible(true)]
     public enum SeekOrigin
     {
         // These constants match Win32's FILE_BEGIN, FILE_CURRENT, and FILE_END
diff --git a/src/mscorlib/src/System/IO/Stream.cs b/src/mscorlib/src/System/IO/Stream.cs
index 3cdfad613e..790f0a09ab 100644
--- a/src/mscorlib/src/System/IO/Stream.cs
+++ b/src/mscorlib/src/System/IO/Stream.cs
@@ -23,14 +23,12 @@ using System.Runtime.InteropServices;
 using System.Runtime.CompilerServices;
 using System.Runtime.ExceptionServices;
 using System.Security;
-using System.Security.Permissions;
 using System.Diagnostics;
 using System.Diagnostics.Contracts;
 using System.Reflection;
 
 namespace System.IO {
     [Serializable]
-    [ComVisible(true)]
     public abstract class Stream : MarshalByRefObject, IDisposable {
 
         public static readonly Stream Null = new NullStream();
@@ -65,7 +63,6 @@ namespace System.IO {
             get;
         }
 
-        [ComVisible(false)]
         public virtual bool CanTimeout {
             [Pure]
             get {
@@ -87,7 +84,6 @@ namespace System.IO {
             set;
         }
 
-        [ComVisible(false)]
         public virtual int ReadTimeout {
             get {
                 Contract.Ensures(Contract.Result<int>() >= 0);
@@ -98,7 +94,6 @@ namespace System.IO {
             }
         }
 
-        [ComVisible(false)]
         public virtual int WriteTimeout {
             get {
                 Contract.Ensures(Contract.Result<int>() >= 0);
@@ -109,7 +104,6 @@ namespace System.IO {
             }
         }
 
-        [ComVisible(false)]
         public Task CopyToAsync(Stream destination)
         {
             int bufferSize = _DefaultCopyBufferSize;
@@ -146,13 +140,11 @@ namespace System.IO {
             return CopyToAsync(destination, bufferSize);
         }
 
-        [ComVisible(false)]
         public Task CopyToAsync(Stream destination, Int32 bufferSize)
         {
             return CopyToAsync(destination, bufferSize, CancellationToken.None);
         }
 
-        [ComVisible(false)]
         public virtual Task CopyToAsync(Stream destination, Int32 bufferSize, CancellationToken cancellationToken)
         {
             StreamHelpers.ValidateCopyToArgs(this, destination, bufferSize);
@@ -278,13 +270,11 @@ namespace System.IO {
 
         public abstract void Flush();
 
-        [ComVisible(false)]
         public Task FlushAsync()
         {
             return FlushAsync(CancellationToken.None);
         }
 
-        [ComVisible(false)]
         public virtual Task FlushAsync(CancellationToken cancellationToken)
         {
             return Task.Factory.StartNew(state => ((Stream)state).Flush(), this,
@@ -398,13 +388,11 @@ namespace System.IO {
             }
         }
 
-        [ComVisible(false)]
         public Task<int> ReadAsync(Byte[] buffer, int offset, int count)
         {
             return ReadAsync(buffer, offset, count, CancellationToken.None);
         }
 
-        [ComVisible(false)]
         public virtual Task<int> ReadAsync(Byte[] buffer, int offset, int count, CancellationToken cancellationToken)
         {
             // If cancellation was requested, bail early with an already completed task.
@@ -617,7 +605,6 @@ namespace System.IO {
                 _buffer = null;
             }
 
-            [MethodImpl(MethodImplOptions.NoInlining)]
             public ReadWriteTask(
                 bool isRead,
                 bool apm,
@@ -630,8 +617,6 @@ namespace System.IO {
                 Contract.Requires(buffer != null);
                 Contract.EndContractBlock();
 
-                StackCrawlMark stackMark = StackCrawlMark.LookForMyCaller;
-
                 // Store the arguments
                 _isRead = isRead;
                 _apm = apm;
@@ -648,8 +633,7 @@ namespace System.IO {
                 if (callback != null)
                 {
                     _callback = callback;
-                    _context = ExecutionContext.Capture(ref stackMark, 
-                        ExecutionContext.CaptureOptions.OptimizeDefaultCase | ExecutionContext.CaptureOptions.IgnoreSyncCtx);
+                    _context = ExecutionContext.Capture();
                     base.AddCompletionAction(this);
                 }
             }
@@ -683,14 +667,13 @@ namespace System.IO {
                     var invokeAsyncCallback = s_invokeAsyncCallback;
                     if (invokeAsyncCallback == null) s_invokeAsyncCallback = invokeAsyncCallback = InvokeAsyncCallback; // benign race condition
 
-                    using(context) ExecutionContext.Run(context, invokeAsyncCallback, this, true);
+                    ExecutionContext.Run(context, invokeAsyncCallback, this);
                 }
             }
 
             bool ITaskCompletionAction.InvokeMayRunArbitraryCode { get { return true; } }
         }
 
-        [ComVisible(false)]
         public Task WriteAsync(Byte[] buffer, int offset, int count)
         {
             return WriteAsync(buffer, offset, count, CancellationToken.None);
@@ -698,7 +681,6 @@ namespace System.IO {
 
 
 
-        [ComVisible(false)]
         public virtual Task WriteAsync(Byte[] buffer, int offset, int count, CancellationToken cancellationToken)
         {
             // If cancellation was requested, bail early with an already completed task.
@@ -906,7 +888,6 @@ namespace System.IO {
             {
             }
 
-            [ComVisible(false)]
             public override Task FlushAsync(CancellationToken cancellationToken)
             {
                 return cancellationToken.IsCancellationRequested ?
@@ -951,7 +932,6 @@ namespace System.IO {
                 return 0;
             }
 
-            [ComVisible(false)]
             public override Task<int> ReadAsync(Byte[] buffer, int offset, int count, CancellationToken cancellationToken)
             {
                 var nullReadTask = s_nullReadTask;
@@ -970,7 +950,6 @@ namespace System.IO {
             {
             }
 
-            [ComVisible(false)]
             public override Task WriteAsync(Byte[] buffer, int offset, int count, CancellationToken cancellationToken)
             {
                 return cancellationToken.IsCancellationRequested ?
@@ -1106,7 +1085,6 @@ namespace System.IO {
                 get { return _stream.CanSeek; }
             }
         
-            [ComVisible(false)]
             public override bool CanTimeout {
                 [Pure]
                 get {
@@ -1135,7 +1113,6 @@ namespace System.IO {
                 }
             }
 
-            [ComVisible(false)]
             public override int ReadTimeout {
                 get {
                     return _stream.ReadTimeout;
@@ -1145,7 +1122,6 @@ namespace System.IO {
                 }
             }
 
-            [ComVisible(false)]
             public override int WriteTimeout {
                 get {
                     return _stream.WriteTimeout;
diff --git a/src/mscorlib/src/System/IO/StreamReader.cs b/src/mscorlib/src/System/IO/StreamReader.cs
index 708db088e8..6d50347b1a 100644
--- a/src/mscorlib/src/System/IO/StreamReader.cs
+++ b/src/mscorlib/src/System/IO/StreamReader.cs
@@ -8,7 +8,6 @@ using System.Runtime.Versioning;
 using System.Diagnostics;
 using System.Diagnostics.CodeAnalysis;
 using System.Diagnostics.Contracts;
-using System.Security.Permissions;
 using System.Threading.Tasks;
 
 namespace System.IO
@@ -18,8 +17,7 @@ namespace System.IO
     // whereas the Stream class is designed for byte input and output.  
     // 
     [Serializable]
-    [System.Runtime.InteropServices.ComVisible(true)]
-    public class StreamReader : TextReader
+    internal class StreamReader : TextReader
     {
         // StreamReader.Null is threadsafe.
         public new static readonly StreamReader Null = new NullStreamReader();
@@ -188,7 +186,7 @@ namespace System.IO
                 throw new ArgumentOutOfRangeException(nameof(bufferSize), Environment.GetResourceString("ArgumentOutOfRange_NeedPosNum"));
             Contract.EndContractBlock();
 
-            Stream stream = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, DefaultFileStreamBufferSize, FileOptions.SequentialScan, Path.GetFileName(path), false, false);
+            Stream stream = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, DefaultFileStreamBufferSize, FileOptions.SequentialScan);
             Init(stream, encoding, detectEncodingFromByteOrderMarks, bufferSize, false);
         }
         
@@ -757,7 +755,6 @@ namespace System.IO
         }
         
         #region Task based Async APIs
-        [ComVisible(false)]
         public override Task<String> ReadLineAsync()
         {
             // If we have been inherited into a subclass, the following implementation could be incorrect
@@ -837,7 +834,6 @@ namespace System.IO
             return GetStringAndReleaseSharedStringBuilder(sb);
         }
 
-        [ComVisible(false)]
         public override Task<String> ReadToEndAsync()
         {
             // If we have been inherited into a subclass, the following implementation could be incorrect
@@ -873,7 +869,6 @@ namespace System.IO
             return GetStringAndReleaseSharedStringBuilder(sb);
         }
 
-        [ComVisible(false)]
         public override Task<int> ReadAsync(char[] buffer, int index, int count)
         {
             if (buffer==null)
@@ -1060,7 +1055,6 @@ namespace System.IO
             return charsRead;
         }
 
-        [ComVisible(false)]
         public override Task<int> ReadBlockAsync(char[] buffer, int index, int count)
         {
             if (buffer==null)
diff --git a/src/mscorlib/src/System/IO/StreamWriter.cs b/src/mscorlib/src/System/IO/StreamWriter.cs
deleted file mode 100644
index 22eba82605..0000000000
--- a/src/mscorlib/src/System/IO/StreamWriter.cs
+++ /dev/null
@@ -1,765 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-// See the LICENSE file in the project root for more information.
-
-using System.Text;
-using System.Runtime.CompilerServices;
-using System.Security.Permissions;
-using System.Runtime.Serialization;
-using System.Diagnostics;
-using System.Diagnostics.Contracts;
-using System.Runtime.InteropServices;
-using System.Threading.Tasks;
-
-namespace System.IO
-{
-    // This class implements a TextWriter for writing characters to a Stream.
-    // This is designed for character output in a particular Encoding, 
-    // whereas the Stream class is designed for byte input and output.  
-    // 
-    [Serializable]
-    [ComVisible(true)]
-    public class StreamWriter : TextWriter
-    {
-        // For UTF-8, the values of 1K for the default buffer size and 4K for the
-        // file stream buffer size are reasonable & give very reasonable
-        // performance for in terms of construction time for the StreamWriter and
-        // write perf.  Note that for UTF-8, we end up allocating a 4K byte buffer,
-        // which means we take advantage of adaptive buffering code.
-        // The performance using UnicodeEncoding is acceptable.  
-        internal const int DefaultBufferSize = 1024;   // char[]
-        private const int DefaultFileStreamBufferSize = 4096;
-        private const int MinBufferSize = 128;
-
-        // Bit bucket - Null has no backing store. Non closable.
-        public new static readonly StreamWriter Null = new StreamWriter(Stream.Null, UTF8NoBOM, MinBufferSize, true);
-
-        private Stream stream;
-        private Encoding encoding;
-        private Encoder encoder;
-        private byte[] byteBuffer;
-        private char[] charBuffer;
-        private int charPos;
-        private int charLen;
-        private bool autoFlush;
-        private bool haveWrittenPreamble;
-        private bool closable;
-
-        // We don't guarantee thread safety on StreamWriter, but we should at 
-        // least prevent users from trying to write anything while an Async
-        // write from the same thread is in progress.
-        [NonSerialized]
-        private volatile Task _asyncWriteTask;
-
-        private void CheckAsyncTaskInProgress()
-        {
-            // We are not locking the access to _asyncWriteTask because this is not meant to guarantee thread safety. 
-            // We are simply trying to deter calling any Write APIs while an async Write from the same thread is in progress.
-            
-            Task t = _asyncWriteTask;
-
-            if (t != null && !t.IsCompleted)
-                throw new InvalidOperationException(Environment.GetResourceString("InvalidOperation_AsyncIOInProgress"));
-        }
-
-        // The high level goal is to be tolerant of encoding errors when we read and very strict 
-        // when we write. Hence, default StreamWriter encoding will throw on encoding error.   
-        // Note: when StreamWriter throws on invalid encoding chars (for ex, high surrogate character 
-        // D800-DBFF without a following low surrogate character DC00-DFFF), it will cause the 
-        // internal StreamWriter's state to be irrecoverable as it would have buffered the 
-        // illegal chars and any subsequent call to Flush() would hit the encoding error again. 
-        // Even Close() will hit the exception as it would try to flush the unwritten data. 
-        // Maybe we can add a DiscardBufferedData() method to get out of such situation (like 
-        // StreamReader though for different reason). Either way, the buffered data will be lost!
-        internal static Encoding UTF8NoBOM {
-            [FriendAccessAllowed]
-            get { return EncodingCache.UTF8NoBOM; }
-        }
-                
-
-        internal StreamWriter(): base(null) { // Ask for CurrentCulture all the time 
-        }
-        
-        public StreamWriter(Stream stream) 
-            : this(stream, UTF8NoBOM, DefaultBufferSize, false) {
-        }
-    
-        public StreamWriter(Stream stream, Encoding encoding) 
-            : this(stream, encoding, DefaultBufferSize, false) {
-        }
-        
-        // Creates a new StreamWriter for the given stream.  The 
-        // character encoding is set by encoding and the buffer size, 
-        // in number of 16-bit characters, is set by bufferSize.  
-        // 
-        public StreamWriter(Stream stream, Encoding encoding, int bufferSize)
-            : this(stream, encoding, bufferSize, false) { 
-        }
-
-        public StreamWriter(Stream stream, Encoding encoding, int bufferSize, bool leaveOpen)
-            : base(null) // Ask for CurrentCulture all the time
-        {
-            if (stream == null || encoding == null)
-                throw new ArgumentNullException((stream == null ? nameof(stream) : nameof(encoding)));
-            if (!stream.CanWrite)
-                throw new ArgumentException(Environment.GetResourceString("Argument_StreamNotWritable"));
-            if (bufferSize <= 0) throw new ArgumentOutOfRangeException(nameof(bufferSize), Environment.GetResourceString("ArgumentOutOfRange_NeedPosNum"));
-            Contract.EndContractBlock();
-
-            Init(stream, encoding, bufferSize, leaveOpen);
-        }
-
-        public StreamWriter(String path) 
-            : this(path, false, UTF8NoBOM, DefaultBufferSize) {
-        }
-
-        public StreamWriter(String path, bool append) 
-            : this(path, append, UTF8NoBOM, DefaultBufferSize) {
-        }
-
-        public StreamWriter(String path, bool append, Encoding encoding) 
-            : this(path, append, encoding, DefaultBufferSize) {
-        }
-
-        public StreamWriter(String path, bool append, Encoding encoding, int bufferSize)
-            : base(null)
-        {
-            // Ask for CurrentCulture all the time
-            if (path == null)
-                throw new ArgumentNullException(nameof(path));
-            if (encoding == null)
-                throw new ArgumentNullException(nameof(encoding));
-            if (path.Length == 0)
-                throw new ArgumentException(Environment.GetResourceString("Argument_EmptyPath"));
-            if (bufferSize <= 0) throw new ArgumentOutOfRangeException(nameof(bufferSize), Environment.GetResourceString("ArgumentOutOfRange_NeedPosNum"));
-            Contract.EndContractBlock();
-
-            Stream stream = CreateFile(path, append);
-            Init(stream, encoding, bufferSize, false);
-        }
-
-        private void Init(Stream streamArg, Encoding encodingArg, int bufferSize, bool shouldLeaveOpen)
-        {
-            this.stream = streamArg;
-            this.encoding = encodingArg;
-            this.encoder = encoding.GetEncoder();
-            if (bufferSize < MinBufferSize) bufferSize = MinBufferSize;
-            charBuffer = new char[bufferSize];
-            byteBuffer = new byte[encoding.GetMaxByteCount(bufferSize)];
-            charLen = bufferSize;
-            // If we're appending to a Stream that already has data, don't write
-            // the preamble.
-            if (stream.CanSeek && stream.Position > 0)
-                haveWrittenPreamble = true;
-            closable = !shouldLeaveOpen;
-        }
-
-        private static Stream CreateFile(String path, bool append) {
-            FileMode mode = append? FileMode.Append: FileMode.Create;
-            FileStream f = new FileStream(path, mode, FileAccess.Write, FileShare.Read,
-                DefaultFileStreamBufferSize, FileOptions.SequentialScan, Path.GetFileName(path), false, false);
-            return f;
-        }
-
-        public override void Close() {
-            Dispose(true);
-            GC.SuppressFinalize(this);
-        }
-
-        protected override void Dispose(bool disposing) {
-            try {
-                // We need to flush any buffered data if we are being closed/disposed.
-                // Also, we never close the handles for stdout & friends.  So we can safely 
-                // write any buffered data to those streams even during finalization, which 
-                // is generally the right thing to do.
-                if (stream != null) {
-                    // Note: flush on the underlying stream can throw (ex., low disk space)
-                    if (disposing)
-                    {
-                        CheckAsyncTaskInProgress();
-
-                        Flush(true, true);
-                    }
-                }
-            }
-            finally {
-                // Dispose of our resources if this StreamWriter is closable. 
-                // Note: Console.Out and other such non closable streamwriters should be left alone 
-                if (!LeaveOpen && stream != null) {
-                    try {
-                        // Attempt to close the stream even if there was an IO error from Flushing.
-                        // Note that Stream.Close() can potentially throw here (may or may not be
-                        // due to the same Flush error). In this case, we still need to ensure 
-                        // cleaning up internal resources, hence the finally block.  
-                        if (disposing)
-                            stream.Close();
-                    }
-                    finally {
-                        stream = null;
-                        byteBuffer = null;
-                        charBuffer = null;
-                        encoding = null;
-                        encoder = null;
-                        charLen = 0;
-                        base.Dispose(disposing);
-                    }
-                }
-            }
-        }
-
-        public override void Flush()
-        {
-            CheckAsyncTaskInProgress();
-
-            Flush(true, true);
-        }
-    
-        private void Flush(bool flushStream, bool flushEncoder)
-        {
-            // flushEncoder should be true at the end of the file and if
-            // the user explicitly calls Flush (though not if AutoFlush is true).
-            // This is required to flush any dangling characters from our UTF-7 
-            // and UTF-8 encoders.  
-            if (stream == null)
-                __Error.WriterClosed();
-
-            // Perf boost for Flush on non-dirty writers.
-            if (charPos==0 && (!flushStream && !flushEncoder))
-                return;
-
-            if (!haveWrittenPreamble) {
-                haveWrittenPreamble = true;
-                byte[] preamble = encoding.GetPreamble();
-                if (preamble.Length > 0)
-                    stream.Write(preamble, 0, preamble.Length);
-            }
-
-            int count = encoder.GetBytes(charBuffer, 0, charPos, byteBuffer, 0, flushEncoder);
-            charPos = 0;
-            if (count > 0)
-                stream.Write(byteBuffer, 0, count);
-            // By definition, calling Flush should flush the stream, but this is
-            // only necessary if we passed in true for flushStream.  The Web
-            // Services guys have some perf tests where flushing needlessly hurts.
-            if (flushStream)
-                stream.Flush();
-        }
-    
-        public virtual bool AutoFlush {
-            get { return autoFlush; }
-
-            set
-            {
-                CheckAsyncTaskInProgress();
-
-                autoFlush = value;
-                if (value) Flush(true, false);
-            }
-        }
-    
-        public virtual Stream BaseStream {
-            get { return stream; }
-        }
-
-        internal bool LeaveOpen {
-            get { return !closable; }
-        }
-
-        internal bool HaveWrittenPreamble {
-            set { haveWrittenPreamble= value; }
-        }
-
-        public override Encoding Encoding {
-            get { return encoding; }
-        }
-
-        public override void Write(char value)
-        {
-            CheckAsyncTaskInProgress();
-
-            if (charPos == charLen) Flush(false, false);
-            charBuffer[charPos] = value;
-            charPos++;
-            if (autoFlush) Flush(true, false);
-        }
-    
-        public override void Write(char[] buffer)
-        {
-            // This may be faster than the one with the index & count since it
-            // has to do less argument checking.
-            if (buffer==null)
-                return;
-
-            CheckAsyncTaskInProgress();
-
-            int index = 0;
-            int count = buffer.Length;
-            while (count > 0) {
-                if (charPos == charLen) Flush(false, false);
-                int n = charLen - charPos;
-                if (n > count) n = count;
-                Debug.Assert(n > 0, "StreamWriter::Write(char[]) isn't making progress!  This is most likely a race condition in user code.");
-                Buffer.InternalBlockCopy(buffer, index * sizeof(char), charBuffer, charPos * sizeof(char), n * sizeof(char));
-                charPos += n;
-                index += n;
-                count -= n;
-            }
-            if (autoFlush) Flush(true, false);
-        }
-
-        public override void Write(char[] buffer, int index, int count) {
-            if (buffer==null)
-                throw new ArgumentNullException(nameof(buffer), Environment.GetResourceString("ArgumentNull_Buffer"));
-            if (index < 0)
-                throw new ArgumentOutOfRangeException(nameof(index), Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
-            if (count < 0)
-                throw new ArgumentOutOfRangeException(nameof(count), Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
-            if (buffer.Length - index < count)
-                throw new ArgumentException(Environment.GetResourceString("Argument_InvalidOffLen"));
-            Contract.EndContractBlock();
-
-            CheckAsyncTaskInProgress();
-
-            while (count > 0) {
-                if (charPos == charLen) Flush(false, false);
-                int n = charLen - charPos;
-                if (n > count) n = count;
-                Debug.Assert(n > 0, "StreamWriter::Write(char[], int, int) isn't making progress!  This is most likely a race condition in user code.");
-                Buffer.InternalBlockCopy(buffer, index * sizeof(char), charBuffer, charPos * sizeof(char), n * sizeof(char));
-                charPos += n;
-                index += n;
-                count -= n;
-            }
-            if (autoFlush) Flush(true, false);
-        }
-    
-        public override void Write(String value)
-        {
-            if (value != null)
-            {
-
-                CheckAsyncTaskInProgress();
-
-                int count = value.Length;
-                int index = 0;
-                while (count > 0) {
-                    if (charPos == charLen) Flush(false, false);
-                    int n = charLen - charPos;
-                    if (n > count) n = count;
-                    Debug.Assert(n > 0, "StreamWriter::Write(String) isn't making progress!  This is most likely a race condition in user code.");
-                    value.CopyTo(index, charBuffer, charPos, n);
-                    charPos += n;
-                    index += n;
-                    count -= n;
-                }
-                if (autoFlush) Flush(true, false);
-            }
-        }
-
-        #region Task based Async APIs
-        [ComVisible(false)]
-        public override Task WriteAsync(char value)
-        {
-            // If we have been inherited into a subclass, the following implementation could be incorrect
-            // since it does not call through to Write() which a subclass might have overriden.  
-            // To be safe we will only use this implementation in cases where we know it is safe to do so,
-            // and delegate to our base class (which will call into Write) when we are not sure.
-            if (this.GetType() != typeof(StreamWriter))
-                return base.WriteAsync(value);
-
-            if (stream == null)
-                __Error.WriterClosed();
-
-            CheckAsyncTaskInProgress();
-
-            Task task = WriteAsyncInternal(this, value, charBuffer, charPos, charLen, CoreNewLine, autoFlush, appendNewLine: false);
-            _asyncWriteTask = task;
-
-            return task;
-        }
-
-        // We pass in private instance fields of this MarshalByRefObject-derived type as local params
-        // to ensure performant access inside the state machine that corresponds this async method.
-        // Fields that are written to must be assigned at the end of the method *and* before instance invocations.
-        private static async Task WriteAsyncInternal(StreamWriter _this, Char value,
-                                                     Char[] charBuffer, Int32 charPos, Int32 charLen, Char[] coreNewLine,
-                                                     bool autoFlush, bool appendNewLine)
-        {            
-            if (charPos == charLen) {
-                await _this.FlushAsyncInternal(false, false, charBuffer, charPos).ConfigureAwait(false);
-                Debug.Assert(_this.charPos == 0);
-                charPos = 0;
-            }
-
-            charBuffer[charPos] = value;
-            charPos++;
-
-            if (appendNewLine)
-            {
-                for (Int32 i = 0; i < coreNewLine.Length; i++)   // Expect 2 iterations, no point calling BlockCopy
-                {
-                    if (charPos == charLen) {                        
-                        await _this.FlushAsyncInternal(false, false, charBuffer, charPos).ConfigureAwait(false);
-                        Debug.Assert(_this.charPos == 0);
-                        charPos = 0;
-                    }
-
-                    charBuffer[charPos] = coreNewLine[i];
-                    charPos++;
-                }
-            }            
-
-            if (autoFlush) {
-                await _this.FlushAsyncInternal(true, false, charBuffer, charPos).ConfigureAwait(false);
-                Debug.Assert(_this.charPos == 0);
-                charPos = 0;
-            }
-
-            _this.CharPos_Prop = charPos;
-        }
-
-        [ComVisible(false)]
-        public override Task WriteAsync(String value)
-        {
-            // If we have been inherited into a subclass, the following implementation could be incorrect
-            // since it does not call through to Write() which a subclass might have overriden.  
-            // To be safe we will only use this implementation in cases where we know it is safe to do so,
-            // and delegate to our base class (which will call into Write) when we are not sure.
-            if (this.GetType() != typeof(StreamWriter))
-                return base.WriteAsync(value);
-
-            if (value != null)
-            {
-                if (stream == null)
-                    __Error.WriterClosed();
-
-                CheckAsyncTaskInProgress();
-
-                Task task = WriteAsyncInternal(this, value, charBuffer, charPos, charLen, CoreNewLine, autoFlush, appendNewLine: false);
-                _asyncWriteTask = task;
-
-                return task;
-            }
-            else
-            {
-                return Task.CompletedTask;
-            }
-        }
-
-        // We pass in private instance fields of this MarshalByRefObject-derived type as local params
-        // to ensure performant access inside the state machine that corresponds this async method.
-        // Fields that are written to must be assigned at the end of the method *and* before instance invocations.
-        private static async Task WriteAsyncInternal(StreamWriter _this, String value,
-                                                     Char[] charBuffer, Int32 charPos, Int32 charLen, Char[] coreNewLine,
-                                                     bool autoFlush, bool appendNewLine)
-        {
-            Contract.Requires(value != null);
-
-            int count = value.Length;
-            int index = 0;
-
-            while (count > 0)
-            {
-                if (charPos == charLen) {
-                    await _this.FlushAsyncInternal(false, false, charBuffer, charPos).ConfigureAwait(false);
-                    Debug.Assert(_this.charPos == 0);
-                    charPos = 0;
-                }
-
-                int n = charLen - charPos;
-                if (n > count)
-                    n = count;
-
-                Debug.Assert(n > 0, "StreamWriter::Write(String) isn't making progress!  This is most likely a race condition in user code.");
-
-                value.CopyTo(index, charBuffer, charPos, n);
-
-                charPos += n;
-                index += n;
-                count -= n;
-            }
-
-            if (appendNewLine)
-            {
-                for (Int32 i = 0; i < coreNewLine.Length; i++)   // Expect 2 iterations, no point calling BlockCopy
-                {
-                    if (charPos == charLen) {
-                        await _this.FlushAsyncInternal(false, false, charBuffer, charPos).ConfigureAwait(false);
-                        Debug.Assert(_this.charPos == 0);
-                        charPos = 0;
-                    }
-
-                    charBuffer[charPos] = coreNewLine[i];
-                    charPos++;
-                }
-            }
-
-            if (autoFlush) {
-                await _this.FlushAsyncInternal(true, false, charBuffer, charPos).ConfigureAwait(false);
-                Debug.Assert(_this.charPos == 0);
-                charPos = 0;
-            }
-
-            _this.CharPos_Prop = charPos;
-        }
-
-        [ComVisible(false)]
-        public override Task WriteAsync(char[] buffer, int index, int count)
-        {
-            if (buffer==null)
-                throw new ArgumentNullException(nameof(buffer), Environment.GetResourceString("ArgumentNull_Buffer"));
-            if (index < 0)
-                throw new ArgumentOutOfRangeException(nameof(index), Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
-            if (count < 0)
-                throw new ArgumentOutOfRangeException(nameof(count), Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
-            if (buffer.Length - index < count)
-                throw new ArgumentException(Environment.GetResourceString("Argument_InvalidOffLen"));
-            Contract.EndContractBlock();
-
-            // If we have been inherited into a subclass, the following implementation could be incorrect
-            // since it does not call through to Write() which a subclass might have overriden.  
-            // To be safe we will only use this implementation in cases where we know it is safe to do so,
-            // and delegate to our base class (which will call into Write) when we are not sure.
-            if (this.GetType() != typeof(StreamWriter))
-                return base.WriteAsync(buffer, index, count);
-
-            if (stream == null)
-                __Error.WriterClosed();
-
-            CheckAsyncTaskInProgress();
-
-            Task task = WriteAsyncInternal(this, buffer, index, count, charBuffer, charPos, charLen, CoreNewLine, autoFlush, appendNewLine: false);
-            _asyncWriteTask = task;
-
-            return task;
-        }
-
-        // We pass in private instance fields of this MarshalByRefObject-derived type as local params
-        // to ensure performant access inside the state machine that corresponds this async method.
-        // Fields that are written to must be assigned at the end of the method *and* before instance invocations.
-        private static async Task WriteAsyncInternal(StreamWriter _this, Char[] buffer, Int32 index, Int32 count,
-                                                     Char[] charBuffer, Int32 charPos, Int32 charLen, Char[] coreNewLine,
-                                                     bool autoFlush, bool appendNewLine)
-        {
-            Contract.Requires(count == 0 || (count > 0 && buffer != null));
-            Contract.Requires(index >= 0);
-            Contract.Requires(count >= 0);
-            Contract.Requires(buffer == null || (buffer != null && buffer.Length - index >= count));
-
-            while (count > 0)
-            {
-                if (charPos == charLen) {
-                    await _this.FlushAsyncInternal(false, false, charBuffer, charPos).ConfigureAwait(false);
-                    Debug.Assert(_this.charPos == 0);
-                    charPos = 0;
-                }
-
-                int n = charLen - charPos;
-                if (n > count) n = count;
-
-                Debug.Assert(n > 0, "StreamWriter::Write(char[], int, int) isn't making progress!  This is most likely a race condition in user code.");
-
-                Buffer.InternalBlockCopy(buffer, index * sizeof(char), charBuffer, charPos * sizeof(char), n * sizeof(char));
-
-                charPos += n;
-                index += n;
-                count -= n;
-            }
-
-            if (appendNewLine)
-            {
-                for (Int32 i = 0; i < coreNewLine.Length; i++)   // Expect 2 iterations, no point calling BlockCopy
-                {
-                    if (charPos == charLen) {
-                        await _this.FlushAsyncInternal(false, false, charBuffer, charPos).ConfigureAwait(false);
-                        Debug.Assert(_this.charPos == 0);
-                        charPos = 0;
-                    }
-
-                    charBuffer[charPos] = coreNewLine[i];
-                    charPos++;
-                }
-            }
-
-            if (autoFlush) {
-                await _this.FlushAsyncInternal(true, false, charBuffer, charPos).ConfigureAwait(false);
-                Debug.Assert(_this.charPos == 0);
-                charPos = 0;
-            }
-
-            _this.CharPos_Prop = charPos;
-        }
-
-        [ComVisible(false)]
-        public override Task WriteLineAsync()
-        {
-            // If we have been inherited into a subclass, the following implementation could be incorrect
-            // since it does not call through to Write() which a subclass might have overriden.  
-            // To be safe we will only use this implementation in cases where we know it is safe to do so,
-            // and delegate to our base class (which will call into Write) when we are not sure.
-            if (this.GetType() != typeof(StreamWriter))
-                return base.WriteLineAsync();
-
-            if (stream == null)
-                __Error.WriterClosed();
-
-            CheckAsyncTaskInProgress();
-
-            Task task = WriteAsyncInternal(this, null, 0, 0, charBuffer, charPos, charLen, CoreNewLine, autoFlush, appendNewLine: true);
-            _asyncWriteTask = task;
-
-            return task;
-        }
-        
-
-        [ComVisible(false)]
-        public override Task WriteLineAsync(char value)
-        {
-            // If we have been inherited into a subclass, the following implementation could be incorrect
-            // since it does not call through to Write() which a subclass might have overriden.  
-            // To be safe we will only use this implementation in cases where we know it is safe to do so,
-            // and delegate to our base class (which will call into Write) when we are not sure.
-            if (this.GetType() != typeof(StreamWriter))
-                return base.WriteLineAsync(value);
-
-            if (stream == null)
-                __Error.WriterClosed();
-
-            CheckAsyncTaskInProgress();
-
-            Task task = WriteAsyncInternal(this, value, charBuffer, charPos, charLen, CoreNewLine, autoFlush, appendNewLine: true);
-            _asyncWriteTask = task;
-
-            return task;
-        }
-        
-
-        [ComVisible(false)]
-        public override Task WriteLineAsync(String value)
-        {
-            // If we have been inherited into a subclass, the following implementation could be incorrect
-            // since it does not call through to Write() which a subclass might have overriden.  
-            // To be safe we will only use this implementation in cases where we know it is safe to do so,
-            // and delegate to our base class (which will call into Write) when we are not sure.
-            if (this.GetType() != typeof(StreamWriter))
-                return base.WriteLineAsync(value);
-
-            if (stream == null)
-                __Error.WriterClosed();
-
-            CheckAsyncTaskInProgress();
-
-            Task task = WriteAsyncInternal(this, value, charBuffer, charPos, charLen, CoreNewLine, autoFlush, appendNewLine: true);
-            _asyncWriteTask = task;
-
-            return task;
-        }
-
-
-        [ComVisible(false)]
-        public override Task WriteLineAsync(char[] buffer, int index, int count)
-        {
-            if (buffer==null)
-                throw new ArgumentNullException(nameof(buffer), Environment.GetResourceString("ArgumentNull_Buffer"));
-            if (index < 0)
-                throw new ArgumentOutOfRangeException(nameof(index), Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
-            if (count < 0)
-                throw new ArgumentOutOfRangeException(nameof(count), Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
-            if (buffer.Length - index < count)
-                throw new ArgumentException(Environment.GetResourceString("Argument_InvalidOffLen"));
-            Contract.EndContractBlock();
-
-            // If we have been inherited into a subclass, the following implementation could be incorrect
-            // since it does not call through to Write() which a subclass might have overriden.  
-            // To be safe we will only use this implementation in cases where we know it is safe to do so,
-            // and delegate to our base class (which will call into Write) when we are not sure.
-            if (this.GetType() != typeof(StreamWriter))
-                return base.WriteLineAsync(buffer, index, count);
-    
-            if (stream == null)
-                __Error.WriterClosed();
-
-            CheckAsyncTaskInProgress();
-
-            Task task = WriteAsyncInternal(this, buffer, index, count, charBuffer, charPos, charLen, CoreNewLine, autoFlush, appendNewLine: true);
-            _asyncWriteTask = task;
-
-            return task;
-        }
-        
-
-        [ComVisible(false)]
-        public override Task FlushAsync()
-        {
-            // If we have been inherited into a subclass, the following implementation could be incorrect
-            // since it does not call through to Flush() which a subclass might have overriden.  To be safe 
-            // we will only use this implementation in cases where we know it is safe to do so,
-            // and delegate to our base class (which will call into Flush) when we are not sure.
-            if (this.GetType() != typeof(StreamWriter))
-                return base.FlushAsync();
-
-            // flushEncoder should be true at the end of the file and if
-            // the user explicitly calls Flush (though not if AutoFlush is true).
-            // This is required to flush any dangling characters from our UTF-7 
-            // and UTF-8 encoders.  
-            if (stream == null)
-                __Error.WriterClosed();
-
-            CheckAsyncTaskInProgress();
-
-            Task task = FlushAsyncInternal(true, true, charBuffer, charPos);
-            _asyncWriteTask = task;
-
-            return task;
-        }
-
-        private Int32 CharPos_Prop {
-            set { this.charPos = value; }
-        }
-
-        private bool HaveWrittenPreamble_Prop {
-            set { this.haveWrittenPreamble = value; }
-        }
-
-        private Task FlushAsyncInternal(bool flushStream, bool flushEncoder,
-                                        Char[] sCharBuffer, Int32 sCharPos) {
-            
-            // Perf boost for Flush on non-dirty writers.
-            if (sCharPos == 0 && !flushStream && !flushEncoder)
-                return Task.CompletedTask;
-
-            Task flushTask = FlushAsyncInternal(this, flushStream, flushEncoder, sCharBuffer, sCharPos, this.haveWrittenPreamble,
-                                                this.encoding, this.encoder, this.byteBuffer, this.stream);
-                                      
-            this.charPos = 0;
-            return flushTask;
-        }
-
-
-        // We pass in private instance fields of this MarshalByRefObject-derived type as local params
-        // to ensure performant access inside the state machine that corresponds this async method.
-        private static async Task FlushAsyncInternal(StreamWriter _this, bool flushStream, bool flushEncoder,
-                                                     Char[] charBuffer, Int32 charPos, bool haveWrittenPreamble,
-                                                     Encoding encoding, Encoder encoder, Byte[] byteBuffer, Stream stream)
-        {            
-            if (!haveWrittenPreamble)
-            {
-                _this.HaveWrittenPreamble_Prop = true;
-                byte[] preamble = encoding.GetPreamble();
-                if (preamble.Length > 0)
-                    await stream.WriteAsync(preamble, 0, preamble.Length).ConfigureAwait(false);
-            }
-
-            int count = encoder.GetBytes(charBuffer, 0, charPos, byteBuffer, 0, flushEncoder);            
-            if (count > 0)
-                await stream.WriteAsync(byteBuffer, 0, count).ConfigureAwait(false);
-
-            // By definition, calling Flush should flush the stream, but this is
-            // only necessary if we passed in true for flushStream.  The Web
-            // Services guys have some perf tests where flushing needlessly hurts.
-            if (flushStream)
-                await stream.FlushAsync().ConfigureAwait(false);
-        }
-        #endregion
-    }  // class StreamWriter
-}  // namespace
diff --git a/src/mscorlib/src/System/IO/TextReader.cs b/src/mscorlib/src/System/IO/TextReader.cs
index 6cbadfbce5..15ba8fba7d 100644
--- a/src/mscorlib/src/System/IO/TextReader.cs
+++ b/src/mscorlib/src/System/IO/TextReader.cs
@@ -17,7 +17,6 @@
 using System.Text;
 using System.Runtime.InteropServices;
 using System.Runtime.CompilerServices;
-using System.Security.Permissions;
 using System.Diagnostics.CodeAnalysis;
 using System.Diagnostics.Contracts;
 using System.Threading;
@@ -32,8 +31,7 @@ namespace System.IO {
     // This class is intended for character input, not bytes.  
     // There are methods on the Stream class for reading bytes. 
     [Serializable]
-    [ComVisible(true)]
-    public abstract class TextReader : MarshalByRefObject, IDisposable {
+    internal abstract class TextReader : MarshalByRefObject, IDisposable {
 
         public static readonly TextReader Null = new NullTextReader();
     
@@ -170,7 +168,6 @@ namespace System.IO {
         }
 
         #region Task based Async APIs
-        [ComVisible(false)]
         public virtual Task<String> ReadLineAsync()
         {
             return Task<String>.Factory.StartNew(state =>
@@ -180,7 +177,6 @@ namespace System.IO {
             this, CancellationToken.None, TaskCreationOptions.DenyChildAttach, TaskScheduler.Default);
         }
 
-        [ComVisible(false)]
         public async virtual Task<String> ReadToEndAsync()
         {
             char[] chars = new char[4096];
@@ -193,7 +189,6 @@ namespace System.IO {
             return sb.ToString();
         }
 
-        [ComVisible(false)]
         public virtual Task<int> ReadAsync(char[] buffer, int index, int count)
         {
             if (buffer==null)
@@ -223,7 +218,6 @@ namespace System.IO {
             tuple, CancellationToken.None, TaskCreationOptions.DenyChildAttach, TaskScheduler.Default);
         }
 
-        [ComVisible(false)]
         public virtual Task<int> ReadBlockAsync(char[] buffer, int index, int count)
         {
             if (buffer==null)
@@ -352,21 +346,18 @@ namespace System.IO {
             // On SyncTextReader all APIs should run synchronously, even the async ones.
             //
 
-            [ComVisible(false)]
             [MethodImplAttribute(MethodImplOptions.Synchronized)]
             public override Task<String> ReadLineAsync()
             {
                 return Task.FromResult(ReadLine());
             }
 
-            [ComVisible(false)]
             [MethodImplAttribute(MethodImplOptions.Synchronized)]
             public override Task<String> ReadToEndAsync()
             {
                 return Task.FromResult(ReadToEnd());
             }
 
-            [ComVisible(false)]
             [MethodImplAttribute(MethodImplOptions.Synchronized)]
             public override Task<int> ReadBlockAsync(char[] buffer, int index, int count)
             {
@@ -382,7 +373,6 @@ namespace System.IO {
                 return Task.FromResult(ReadBlock(buffer, index, count));
             }
 
-            [ComVisible(false)]
             [MethodImplAttribute(MethodImplOptions.Synchronized)]
             public override Task<int> ReadAsync(char[] buffer, int index, int count)
             {
diff --git a/src/mscorlib/src/System/IO/TextWriter.cs b/src/mscorlib/src/System/IO/TextWriter.cs
deleted file mode 100644
index 131f69d35d..0000000000
--- a/src/mscorlib/src/System/IO/TextWriter.cs
+++ /dev/null
@@ -1,886 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-// See the LICENSE file in the project root for more information.
-
-using System.Text;
-using System.Threading;
-using System.Runtime.CompilerServices;
-using System.Runtime.InteropServices;
-using System.Security.Permissions;
-using System.Globalization;
-using System.Diagnostics.CodeAnalysis;
-using System.Diagnostics.Contracts;
-using System.Threading.Tasks;
-
-namespace System.IO {
-    // This abstract base class represents a writer that can write a sequential
-    // stream of characters. A subclass must minimally implement the 
-    // Write(char) method.
-    //
-    // This class is intended for character output, not bytes.  
-    // There are methods on the Stream class for writing bytes. 
-    [Serializable]
-    [ComVisible(true)]
-    public abstract class TextWriter : MarshalByRefObject, IDisposable {
-        public static readonly TextWriter Null = new NullTextWriter();
-
-        // This should be initialized to Environment.NewLine, but
-        // to avoid loading Environment unnecessarily so I've duplicated
-        // the value here.
-#if !PLATFORM_UNIX
-        private const String InitialNewLine = "\r\n";
-
-        protected char[] CoreNewLine = new char[] { '\r', '\n' };
-#else
-        private const String InitialNewLine = "\n";
-
-        protected char[] CoreNewLine = new char[] {'\n'};
-#endif // !PLATFORM_UNIX
-
-        // Can be null - if so, ask for the Thread's CurrentCulture every time.
-        private IFormatProvider InternalFormatProvider;
-
-        protected TextWriter()
-        {
-            InternalFormatProvider = null;  // Ask for CurrentCulture all the time.
-        }
-    
-        protected TextWriter(IFormatProvider formatProvider)
-        {
-            InternalFormatProvider = formatProvider;
-        }
-
-        public virtual IFormatProvider FormatProvider {
-            get { 
-                if (InternalFormatProvider == null)
-                    return Thread.CurrentThread.CurrentCulture;
-                else
-                    return InternalFormatProvider;
-            }
-        }
-
-        // Closes this TextWriter and releases any system resources associated with the
-        // TextWriter. Following a call to Close, any operations on the TextWriter
-        // may raise exceptions. This default method is empty, but descendant
-        // classes can override the method to provide the appropriate
-        // functionality.
-        public virtual void Close() {
-            Dispose(true);
-            GC.SuppressFinalize(this);
-        }
-
-        protected virtual void Dispose(bool disposing)
-        {
-        }
-
-
-        public void Dispose()
-        {
-            Dispose(true);
-            GC.SuppressFinalize(this);
-        }
-    
-        // Clears all buffers for this TextWriter and causes any buffered data to be
-        // written to the underlying device. This default method is empty, but
-        // descendant classes can override the method to provide the appropriate
-        // functionality.
-        public virtual void Flush() {
-        }
-
-        public abstract Encoding Encoding {
-            get;
-        }
-
-        // Returns the line terminator string used by this TextWriter. The default line
-        // terminator string is a carriage return followed by a line feed ("\r\n").
-        //
-        // Sets the line terminator string for this TextWriter. The line terminator
-        // string is written to the text stream whenever one of the
-        // WriteLine methods are called. In order for text written by
-        // the TextWriter to be readable by a TextReader, only one of the following line
-        // terminator strings should be used: "\r", "\n", or "\r\n".
-        // 
-        public virtual String NewLine {
-            get { return new String(CoreNewLine); }
-            set {
-                if (value == null) 
-                    value = InitialNewLine;
-                CoreNewLine = value.ToCharArray();
-            }
-        }
-    
-
-        public static TextWriter Synchronized(TextWriter writer) {
-            if (writer==null)
-                throw new ArgumentNullException(nameof(writer));
-            Contract.Ensures(Contract.Result<TextWriter>() != null);
-            Contract.EndContractBlock();
-
-            if (writer is SyncTextWriter)
-                return writer;
-            
-            return new SyncTextWriter(writer);
-        }
-        
-        // Writes a character to the text stream. This default method is empty,
-        // but descendant classes can override the method to provide the
-        // appropriate functionality.
-        //
-        public virtual void Write(char value) {
-        }
-    
-        // Writes a character array to the text stream. This default method calls
-        // Write(char) for each of the characters in the character array.
-        // If the character array is null, nothing is written.
-        //
-        public virtual void Write(char[] buffer) {
-            if (buffer != null) Write(buffer, 0, buffer.Length);
-        }
-    
-        // Writes a range of a character array to the text stream. This method will
-        // write count characters of data into this TextWriter from the
-        // buffer character array starting at position index.
-        //
-        public virtual void Write(char[] buffer, int index, int count) {
-            if (buffer==null)
-                throw new ArgumentNullException(nameof(buffer), Environment.GetResourceString("ArgumentNull_Buffer"));
-            if (index < 0)
-                throw new ArgumentOutOfRangeException(nameof(index), Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
-            if (count < 0)
-                throw new ArgumentOutOfRangeException(nameof(count), Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
-            if (buffer.Length - index < count)
-                throw new ArgumentException(Environment.GetResourceString("Argument_InvalidOffLen"));
-            Contract.EndContractBlock();
-
-            for (int i = 0; i < count; i++) Write(buffer[index + i]);
-        }
-    
-        // Writes the text representation of a boolean to the text stream. This
-        // method outputs either Boolean.TrueString or Boolean.FalseString.
-        //
-        public virtual void Write(bool value) {
-            Write(value ? Boolean.TrueLiteral : Boolean.FalseLiteral);
-        }
-    
-        // Writes the text representation of an integer to the text stream. The
-        // text representation of the given value is produced by calling the
-        // Int32.ToString() method.
-        //
-        public virtual void Write(int value) {
-            Write(value.ToString(FormatProvider));
-        }
-    
-        // Writes the text representation of an integer to the text stream. The
-        // text representation of the given value is produced by calling the
-        // UInt32.ToString() method.
-        //
-        [CLSCompliant(false)]
-        public virtual void Write(uint value) {
-            Write(value.ToString(FormatProvider));
-        }
-    
-        // Writes the text representation of a long to the text stream. The
-        // text representation of the given value is produced by calling the
-        // Int64.ToString() method.
-        //
-        public virtual void Write(long value) {
-            Write(value.ToString(FormatProvider));
-        }
-    
-        // Writes the text representation of an unsigned long to the text 
-        // stream. The text representation of the given value is produced 
-        // by calling the UInt64.ToString() method.
-        //
-        [CLSCompliant(false)]
-        public virtual void Write(ulong value) {
-            Write(value.ToString(FormatProvider));
-        }
-    
-        // Writes the text representation of a float to the text stream. The
-        // text representation of the given value is produced by calling the
-        // Float.toString(float) method.
-        //
-        public virtual void Write(float value) {
-            Write(value.ToString(FormatProvider));
-        }
-    
-        // Writes the text representation of a double to the text stream. The
-        // text representation of the given value is produced by calling the
-        // Double.toString(double) method.
-        //
-        public virtual void Write(double value) {
-            Write(value.ToString(FormatProvider));
-        }
-    
-        public virtual void Write(Decimal value) {
-            Write(value.ToString(FormatProvider));
-        }
-    
-        // Writes a string to the text stream. If the given string is null, nothing
-        // is written to the text stream.
-        //
-        public virtual void Write(String value) {
-            if (value != null) Write(value.ToCharArray());
-        }
-    
-        // Writes the text representation of an object to the text stream. If the
-        // given object is null, nothing is written to the text stream.
-        // Otherwise, the object's ToString method is called to produce the
-        // string representation, and the resulting string is then written to the
-        // output stream.
-        //
-        public virtual void Write(Object value) {
-            if (value != null) {
-                IFormattable f = value as IFormattable;
-                if (f != null)
-                    Write(f.ToString(null, FormatProvider));
-                else
-                    Write(value.ToString());
-            }
-        }
-    
-#if false
-    //      // Converts the wchar * to a string and writes this to the stream.
-    //      //
-    //      __attribute NonCLSCompliantAttribute()
-    //      public void Write(wchar *value) {
-    //          Write(new String(value));
-    //      }
-    
-    //      // Treats the byte* as a LPCSTR, converts it to a string, and writes it to the stream.
-    //      // 
-    //      __attribute NonCLSCompliantAttribute()
-    //      public void Write(byte *value) {
-    //          Write(new String(value));
-    //      }
-#endif
-    
-    
-        // Writes out a formatted string.  Uses the same semantics as
-        // String.Format.
-        // 
-        public virtual void Write(String format, Object arg0)
-        {
-            Write(String.Format(FormatProvider, format, arg0));
-        }
-        
-        // Writes out a formatted string.  Uses the same semantics as
-        // String.Format.
-        // 
-        public virtual void Write(String format, Object arg0, Object arg1)
-        {
-            Write(String.Format(FormatProvider, format, arg0, arg1));
-        }
-        
-        // Writes out a formatted string.  Uses the same semantics as
-        // String.Format.
-        // 
-        public virtual void Write(String format, Object arg0, Object arg1, Object arg2)
-        {
-            Write(String.Format(FormatProvider, format, arg0, arg1, arg2));
-        }
-        
-        // Writes out a formatted string.  Uses the same semantics as
-        // String.Format.
-        // 
-        public virtual void Write(String format, params Object[] arg)
-        {
-            Write(String.Format(FormatProvider, format, arg));
-        }
-        
-    
-        // Writes a line terminator to the text stream. The default line terminator
-        // is a carriage return followed by a line feed ("\r\n"), but this value
-        // can be changed by setting the NewLine property.
-        //
-        public virtual void WriteLine() {
-            Write(CoreNewLine);
-        }
-    
-        // Writes a character followed by a line terminator to the text stream.
-        //
-        public virtual void WriteLine(char value) {
-            Write(value);
-            WriteLine();
-        }
-    
-        // Writes an array of characters followed by a line terminator to the text
-        // stream.
-        //
-        public virtual void WriteLine(char[] buffer) {
-            Write(buffer);
-            WriteLine();
-        }
-    
-        // Writes a range of a character array followed by a line terminator to the
-        // text stream.
-        //
-        public virtual void WriteLine(char[] buffer, int index, int count) {
-            Write(buffer, index, count);
-            WriteLine();
-        }
-    
-        // Writes the text representation of a boolean followed by a line
-        // terminator to the text stream.
-        //
-        public virtual void WriteLine(bool value) {
-            Write(value);
-            WriteLine();
-        }
-    
-        // Writes the text representation of an integer followed by a line
-        // terminator to the text stream.
-        //
-        public virtual void WriteLine(int value) {
-            Write(value);
-            WriteLine();
-        }
-    
-        // Writes the text representation of an unsigned integer followed by 
-        // a line terminator to the text stream.
-        //
-        [CLSCompliant(false)]
-        public virtual void WriteLine(uint value) {
-            Write(value);
-            WriteLine();
-        }
-    
-        // Writes the text representation of a long followed by a line terminator
-        // to the text stream.
-        //
-        public virtual void WriteLine(long value) {
-            Write(value);
-            WriteLine();
-        }
-    
-        // Writes the text representation of an unsigned long followed by 
-        // a line terminator to the text stream.
-        //
-        [CLSCompliant(false)]
-        public virtual void WriteLine(ulong value) {
-            Write(value);
-            WriteLine();
-        }
-    
-        // Writes the text representation of a float followed by a line terminator
-        // to the text stream.
-        //
-        public virtual void WriteLine(float value) {
-            Write(value);
-            WriteLine();
-        }
-    
-        // Writes the text representation of a double followed by a line terminator
-        // to the text stream.
-        //
-        public virtual void WriteLine(double value) {
-            Write(value);
-            WriteLine();
-        }
-
-        public virtual void WriteLine(decimal value) {
-            Write(value);
-            WriteLine();
-        }
-    
-        // Writes a string followed by a line terminator to the text stream.
-        //
-        public virtual void WriteLine(String value) {
-
-            if (value==null) {
-                WriteLine();
-            }
-            else {
-                // We'd ideally like WriteLine to be atomic, in that one call
-                // to WriteLine equals one call to the OS (ie, so writing to 
-                // console while simultaneously calling printf will guarantee we
-                // write out a string and new line chars, without any interference).
-                // Additionally, we need to call ToCharArray on Strings anyways,
-                // so allocating a char[] here isn't any worse than what we were
-                // doing anyways.  We do reduce the number of calls to the 
-                // backing store this way, potentially.
-                int vLen = value.Length;
-                int nlLen = CoreNewLine.Length;
-                char[] chars = new char[vLen+nlLen];
-                value.CopyTo(0, chars, 0, vLen);
-                // CoreNewLine will almost always be 2 chars, and possibly 1.
-                if (nlLen == 2) {
-                    chars[vLen] = CoreNewLine[0];
-                    chars[vLen+1] = CoreNewLine[1];
-                }
-                else if (nlLen == 1)
-                    chars[vLen] = CoreNewLine[0];
-                else
-                    Buffer.InternalBlockCopy(CoreNewLine, 0, chars, vLen * 2, nlLen * 2);
-                Write(chars, 0, vLen + nlLen);
-            }
-            /*
-            Write(value);  // We could call Write(String) on StreamWriter...
-            WriteLine();
-            */
-        }
-    
-        // Writes the text representation of an object followed by a line
-        // terminator to the text stream.
-        //
-        public virtual void WriteLine(Object value) {
-            if (value==null) {
-                WriteLine();
-            }
-            else {
-                // Call WriteLine(value.ToString), not Write(Object), WriteLine().
-                // This makes calls to WriteLine(Object) atomic.
-                IFormattable f = value as IFormattable;
-                if (f != null)
-                    WriteLine(f.ToString(null, FormatProvider));
-                else
-                    WriteLine(value.ToString());
-            }
-        }
-
-        // Writes out a formatted string and a new line.  Uses the same 
-        // semantics as String.Format.
-        // 
-        public virtual void WriteLine(String format, Object arg0)
-        {
-            WriteLine(String.Format(FormatProvider, format, arg0));
-        }
-        
-        // Writes out a formatted string and a new line.  Uses the same 
-        // semantics as String.Format.
-        // 
-        public virtual void WriteLine (String format, Object arg0, Object arg1)
-        {
-            WriteLine(String.Format(FormatProvider, format, arg0, arg1));
-        }
-        
-        // Writes out a formatted string and a new line.  Uses the same 
-        // semantics as String.Format.
-        // 
-        public virtual void WriteLine (String format, Object arg0, Object arg1, Object arg2)
-        {
-            WriteLine(String.Format(FormatProvider, format, arg0, arg1, arg2));
-        }
-        
-        // Writes out a formatted string and a new line.  Uses the same 
-        // semantics as String.Format.
-        // 
-        public virtual void WriteLine (String format, params Object[] arg)
-        {
-            WriteLine(String.Format(FormatProvider, format, arg));
-        }
-
-        #region Task based Async APIs
-        [ComVisible(false)]
-        public virtual Task WriteAsync(char value)
-        {
-            var tuple = new Tuple<TextWriter, char>(this, value);
-            return Task.Factory.StartNew(state =>
-            {
-                var t = (Tuple<TextWriter, char>)state;
-                t.Item1.Write(t.Item2);
-            },
-            tuple, CancellationToken.None, TaskCreationOptions.DenyChildAttach, TaskScheduler.Default);
-        }
-
-        [ComVisible(false)]
-        public virtual Task WriteAsync(String value)
-        {
-            var tuple = new Tuple<TextWriter, string>(this, value);
-            return Task.Factory.StartNew(state =>
-            {
-                var t = (Tuple<TextWriter, string>)state;
-                t.Item1.Write(t.Item2);
-            },
-            tuple, CancellationToken.None, TaskCreationOptions.DenyChildAttach, TaskScheduler.Default);
-        }
-
-        [ComVisible(false)]
-        public Task WriteAsync(char[] buffer)
-        {
-            if (buffer == null)  return Task.CompletedTask;
-            return WriteAsync(buffer, 0, buffer.Length);
-        }
-
-        [ComVisible(false)]
-        public virtual Task WriteAsync(char[] buffer, int index, int count)
-        {
-            var tuple = new Tuple<TextWriter, char[], int, int>(this, buffer, index, count);
-            return Task.Factory.StartNew(state =>
-            {
-                var t = (Tuple<TextWriter, char[], int, int>)state;
-                t.Item1.Write(t.Item2, t.Item3, t.Item4);
-            },
-            tuple, CancellationToken.None, TaskCreationOptions.DenyChildAttach, TaskScheduler.Default);
-        }
-
-        [ComVisible(false)]
-        public virtual Task WriteLineAsync(char value)
-        {
-            var tuple = new Tuple<TextWriter, char>(this, value);
-            return Task.Factory.StartNew(state =>
-            {
-                var t = (Tuple<TextWriter, char>)state;
-                t.Item1.WriteLine(t.Item2);
-            },
-            tuple, CancellationToken.None, TaskCreationOptions.DenyChildAttach, TaskScheduler.Default);
-        }
-
-        [ComVisible(false)]
-        public virtual Task WriteLineAsync(String value)
-        {
-            var tuple = new Tuple<TextWriter, string>(this, value);
-            return Task.Factory.StartNew(state =>
-            {
-                var t = (Tuple<TextWriter, string>)state;
-                t.Item1.WriteLine(t.Item2);
-            },
-            tuple, CancellationToken.None, TaskCreationOptions.DenyChildAttach, TaskScheduler.Default);
-        }
-
-        [ComVisible(false)]
-        public Task WriteLineAsync(char[] buffer)
-        {
-            if (buffer == null)  return Task.CompletedTask;
-            return WriteLineAsync(buffer, 0, buffer.Length);
-        }
-
-        [ComVisible(false)]
-        public virtual Task WriteLineAsync(char[] buffer, int index, int count)
-        {
-            var tuple = new Tuple<TextWriter, char[], int, int>(this, buffer, index, count);
-            return Task.Factory.StartNew(state =>
-            {
-                var t = (Tuple<TextWriter, char[], int, int>)state;
-                t.Item1.WriteLine(t.Item2, t.Item3, t.Item4);
-            },
-            tuple, CancellationToken.None, TaskCreationOptions.DenyChildAttach, TaskScheduler.Default);
-        }
-
-        [ComVisible(false)]
-        public virtual Task WriteLineAsync()
-        {
-            return WriteAsync(CoreNewLine);
-        }
-
-        [ComVisible(false)]
-        public virtual Task FlushAsync()
-        {
-            return Task.Factory.StartNew(state =>
-            {
-                ((TextWriter)state).Flush();
-            },
-            this, CancellationToken.None, TaskCreationOptions.DenyChildAttach, TaskScheduler.Default);
-        }
-        #endregion
-
-        [Serializable]
-        private sealed class NullTextWriter : TextWriter
-        {
-            internal NullTextWriter(): base(CultureInfo.InvariantCulture) {
-            }
-        
-            public override Encoding Encoding {
-                get { return Encoding.Default;  }
-            }
-
-            [SuppressMessage("Microsoft.Contracts", "CC1055")]  // Skip extra error checking to avoid *potential* AppCompat problems.
-            public override void Write(char[] buffer, int index, int count) {
-            }
-            
-            public override void Write(String value) {
-            }
-
-            // Not strictly necessary, but for perf reasons
-            public override void WriteLine() {
-            }
-
-            // Not strictly necessary, but for perf reasons
-            public override void WriteLine(String value) {
-            }
-            
-            public override void WriteLine(Object value) {
-            }
-        }
-        
-        [Serializable]
-        internal sealed class SyncTextWriter : TextWriter, IDisposable
-        {
-            private TextWriter _out;
-            
-            internal SyncTextWriter(TextWriter t): base(t.FormatProvider) {
-                _out = t;
-            }
-
-            public override Encoding Encoding {
-                get { return _out.Encoding;  }
-            }
-
-            public override IFormatProvider FormatProvider {
-                get { return _out.FormatProvider;  }
-            }
-            
-            public override  String NewLine {
-                [MethodImplAttribute(MethodImplOptions.Synchronized)]
-                get { return _out.NewLine; }
-                [MethodImplAttribute(MethodImplOptions.Synchronized)]
-                set { _out.NewLine = value; }
-            }
-    
-            [MethodImplAttribute(MethodImplOptions.Synchronized)]
-            public override void Close() {
-                // So that any overriden Close() gets run
-                _out.Close();
-            }
-
-            [MethodImplAttribute(MethodImplOptions.Synchronized)]
-            protected override void Dispose(bool disposing) {
-                // Explicitly pick up a potentially methodimpl'ed Dispose
-                if (disposing)
-                    ((IDisposable)_out).Dispose();
-            }
-
-            [MethodImplAttribute(MethodImplOptions.Synchronized)]
-            public override void Flush() {
-                _out.Flush();
-            }
-    
-            [MethodImplAttribute(MethodImplOptions.Synchronized)]
-            public override void Write(char value) {
-                _out.Write(value);
-            }
-    
-            [MethodImplAttribute(MethodImplOptions.Synchronized)]
-            public override void Write(char[] buffer) {
-                _out.Write(buffer);
-            }
-
-            [SuppressMessage("Microsoft.Contracts", "CC1055")]  // Skip extra error checking to avoid *potential* AppCompat problems.
-            [MethodImplAttribute(MethodImplOptions.Synchronized)]
-            public override void Write(char[] buffer, int index, int count) {
-                _out.Write(buffer, index, count);
-            }
-
-            [MethodImplAttribute(MethodImplOptions.Synchronized)]
-            public override void Write(bool value) {
-                _out.Write(value);
-            }
-            
-            [MethodImplAttribute(MethodImplOptions.Synchronized)]
-            public override void Write(int value) {
-                _out.Write(value);
-            }
-            
-            [MethodImplAttribute(MethodImplOptions.Synchronized)]
-            public override void Write(uint value) {
-                _out.Write(value);
-            }
-            
-            [MethodImplAttribute(MethodImplOptions.Synchronized)]
-            public override void Write(long value) {
-                _out.Write(value);
-            }
-            
-            [MethodImplAttribute(MethodImplOptions.Synchronized)]
-            public override void Write(ulong value) {
-                _out.Write(value);
-            }
-            
-            [MethodImplAttribute(MethodImplOptions.Synchronized)]
-            public override void Write(float value) {
-                _out.Write(value);
-            }
-            
-            [MethodImplAttribute(MethodImplOptions.Synchronized)]
-            public override void Write(double value) {
-                _out.Write(value);
-            }
-            
-            [MethodImplAttribute(MethodImplOptions.Synchronized)]
-            public override void Write(Decimal value) {
-                _out.Write(value);
-            }
-
-            [MethodImplAttribute(MethodImplOptions.Synchronized)]
-            public override void Write(String value) {
-                _out.Write(value);
-            }
-            
-            [MethodImplAttribute(MethodImplOptions.Synchronized)]
-            public override void Write(Object value) {
-                _out.Write(value);
-            }
-            
-            [MethodImplAttribute(MethodImplOptions.Synchronized)]
-            public override void Write(String format, Object arg0) {
-                _out.Write(format, arg0);
-            }
-            
-            [MethodImplAttribute(MethodImplOptions.Synchronized)]
-            public override void Write(String format, Object arg0, Object arg1) {
-                _out.Write(format, arg0, arg1);
-            }
-            
-            [MethodImplAttribute(MethodImplOptions.Synchronized)]
-            public override void Write(String format, Object arg0, Object arg1, Object arg2) {
-                _out.Write(format, arg0, arg1, arg2);
-            }
-            
-            [MethodImplAttribute(MethodImplOptions.Synchronized)]
-            public override void Write(String format, Object[] arg) {
-                _out.Write(format, arg);
-            }
-    
-            [MethodImplAttribute(MethodImplOptions.Synchronized)]
-            public override void WriteLine() {
-                _out.WriteLine();
-            }
-    
-            [MethodImplAttribute(MethodImplOptions.Synchronized)]
-            public override void WriteLine(char value) {
-                _out.WriteLine(value);
-            }
-    
-            [MethodImplAttribute(MethodImplOptions.Synchronized)]
-            public override void WriteLine(decimal value) {
-                _out.WriteLine(value);
-            }
-    
-            [MethodImplAttribute(MethodImplOptions.Synchronized)]
-            public override void WriteLine(char[] buffer) {
-                _out.WriteLine(buffer);
-            }
-            
-            [MethodImplAttribute(MethodImplOptions.Synchronized)]
-            public override void WriteLine(char[] buffer, int index, int count) {
-                _out.WriteLine(buffer, index, count);
-            }
-            
-            [MethodImplAttribute(MethodImplOptions.Synchronized)]
-            public override void WriteLine(bool value) {
-                _out.WriteLine(value);
-            }
-            
-            [MethodImplAttribute(MethodImplOptions.Synchronized)]
-            public override void WriteLine(int value) {
-                _out.WriteLine(value);
-            }
-            
-            [MethodImplAttribute(MethodImplOptions.Synchronized)]
-            public override void WriteLine(uint value) {
-                _out.WriteLine(value);
-            }
-            
-            [MethodImplAttribute(MethodImplOptions.Synchronized)]
-            public override void WriteLine(long value) {
-                _out.WriteLine(value);
-            }
-            
-            [MethodImplAttribute(MethodImplOptions.Synchronized)]
-            public override void WriteLine(ulong value) {
-                _out.WriteLine(value);
-            }
-            
-            [MethodImplAttribute(MethodImplOptions.Synchronized)]
-            public override void WriteLine(float value) {
-                _out.WriteLine(value);
-            }
-            
-            [MethodImplAttribute(MethodImplOptions.Synchronized)]
-            public override void WriteLine(double value) {
-                _out.WriteLine(value);
-            }
-            
-            [MethodImplAttribute(MethodImplOptions.Synchronized)]
-            public override void WriteLine(String value) {
-                _out.WriteLine(value);
-            }
-            
-            [MethodImplAttribute(MethodImplOptions.Synchronized)]
-            public override void WriteLine(Object value) {
-                _out.WriteLine(value);
-            }
-            
-            [MethodImplAttribute(MethodImplOptions.Synchronized)]
-            public override void WriteLine(String format, Object arg0) {
-                _out.WriteLine(format, arg0);
-            }
-            
-            [MethodImplAttribute(MethodImplOptions.Synchronized)]
-            public override void WriteLine(String format, Object arg0, Object arg1) {
-                _out.WriteLine(format, arg0, arg1);
-            }
-            
-            [MethodImplAttribute(MethodImplOptions.Synchronized)]
-            public override void WriteLine(String format, Object arg0, Object arg1, Object arg2) {
-                _out.WriteLine(format, arg0, arg1, arg2);
-            }
-            
-            [MethodImplAttribute(MethodImplOptions.Synchronized)]
-            public override void WriteLine(String format, Object[] arg) {
-                _out.WriteLine(format, arg);
-            }
-
-
-            //
-            // On SyncTextWriter all APIs should run synchronously, even the async ones.
-            //
-
-            [MethodImplAttribute(MethodImplOptions.Synchronized)]
-            [ComVisible(false)]
-            public override Task WriteAsync(char value)
-            {
-                Write(value);
-                return Task.CompletedTask;
-            }
-
-            [MethodImplAttribute(MethodImplOptions.Synchronized)]
-            [ComVisible(false)]
-            public override Task WriteAsync(String value)
-            {
-                Write(value);
-                return Task.CompletedTask;
-            }
-
-            [MethodImplAttribute(MethodImplOptions.Synchronized)]
-            [ComVisible(false)]
-            public override Task WriteAsync(char[] buffer, int index, int count)
-            {
-                Write(buffer, index, count);
-                return Task.CompletedTask;
-            }
-
-            [MethodImplAttribute(MethodImplOptions.Synchronized)]
-            [ComVisible(false)]
-            public override Task WriteLineAsync(char value)
-            {
-                WriteLine(value);
-                return Task.CompletedTask;
-            }
-
-            [MethodImplAttribute(MethodImplOptions.Synchronized)]
-            [ComVisible(false)]
-            public override Task WriteLineAsync(String value)
-            {
-                WriteLine(value);
-                return Task.CompletedTask;
-            }
-
-            [MethodImplAttribute(MethodImplOptions.Synchronized)]
-            [ComVisible(false)]
-            public override Task WriteLineAsync(char[] buffer, int index, int count)
-            {
-                WriteLine(buffer, index, count);
-                return Task.CompletedTask;
-            }
-
-            [MethodImplAttribute(MethodImplOptions.Synchronized)]
-            [ComVisible(false)]
-            public override Task FlushAsync()
-            {
-                Flush();
-                return Task.CompletedTask;
-            }
-        }
-    }
-}
diff --git a/src/mscorlib/src/System/IO/UnmanagedMemoryAccessor.cs b/src/mscorlib/src/System/IO/UnmanagedMemoryAccessor.cs
index 4208ebfb6d..f3fd71833c 100644
--- a/src/mscorlib/src/System/IO/UnmanagedMemoryAccessor.cs
+++ b/src/mscorlib/src/System/IO/UnmanagedMemoryAccessor.cs
@@ -17,7 +17,6 @@ using System.Runtime.InteropServices;
 using System.Runtime.CompilerServices;
 using System.Runtime.ConstrainedExecution;
 using System.Runtime.Versioning;
-using System.Security.Permissions;
 using Microsoft.Win32.SafeHandles;
 using System.Diagnostics;
 using System.Diagnostics.Contracts;
diff --git a/src/mscorlib/src/System/IO/UnmanagedMemoryStream.cs b/src/mscorlib/src/System/IO/UnmanagedMemoryStream.cs
index d78632639b..165b6d2b19 100644
--- a/src/mscorlib/src/System/IO/UnmanagedMemoryStream.cs
+++ b/src/mscorlib/src/System/IO/UnmanagedMemoryStream.cs
@@ -17,7 +17,6 @@ using System.Runtime;
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
 using System.Security;
-using System.Security.Permissions;
 using System.Threading;
 using System.Diagnostics;
 using System.Diagnostics.Contracts;
@@ -108,25 +107,14 @@ namespace System.IO {
         }
 
         public UnmanagedMemoryStream(SafeBuffer buffer, long offset, long length) {
-            Initialize(buffer, offset, length, FileAccess.Read, false);
+            Initialize(buffer, offset, length, FileAccess.Read);
         }
 
         public UnmanagedMemoryStream(SafeBuffer buffer, long offset, long length, FileAccess access) {
-            Initialize(buffer, offset, length, access, false);
-        }
-
-        // We must create one of these without doing a security check.  This
-        // class is created while security is trying to start up.  Plus, doing
-        // a Demand from Assembly.GetManifestResourceStream isn't useful.
-        internal UnmanagedMemoryStream(SafeBuffer buffer, long offset, long length, FileAccess access, bool skipSecurityCheck) {
-            Initialize(buffer, offset, length, access, skipSecurityCheck);
+            Initialize(buffer, offset, length, access);
         }
 
         protected void Initialize(SafeBuffer buffer, long offset, long length, FileAccess access) {
-            Initialize(buffer, offset, length, access, false);
-        }
-
-        internal void Initialize(SafeBuffer buffer, long offset, long length, FileAccess access, bool skipSecurityCheck) {
             if (buffer == null) {
                 throw new ArgumentNullException(nameof(buffer));
             }
@@ -147,11 +135,6 @@ namespace System.IO {
             if (_isOpen) {
                 throw new InvalidOperationException(Environment.GetResourceString("InvalidOperation_CalledTwice"));
             }
-            if (!skipSecurityCheck) {
-#pragma warning disable 618
-                new SecurityPermission(SecurityPermissionFlag.UnmanagedCode).Demand();
-#pragma warning restore 618
-            }
 
             // check for wraparound
             unsafe {
@@ -181,31 +164,18 @@ namespace System.IO {
         [CLSCompliant(false)]
         public unsafe UnmanagedMemoryStream(byte* pointer, long length)
         {
-            Initialize(pointer, length, length, FileAccess.Read, false);
+            Initialize(pointer, length, length, FileAccess.Read);
         }
 
         [CLSCompliant(false)]
         public unsafe UnmanagedMemoryStream(byte* pointer, long length, long capacity, FileAccess access) 
         {
-            Initialize(pointer, length, capacity, access, false);
-        }
-
-        // We must create one of these without doing a security check.  This
-        // class is created while security is trying to start up.  Plus, doing
-        // a Demand from Assembly.GetManifestResourceStream isn't useful.
-        internal unsafe UnmanagedMemoryStream(byte* pointer, long length, long capacity, FileAccess access, bool skipSecurityCheck) 
-        {
-            Initialize(pointer, length, capacity, access, skipSecurityCheck);
+            Initialize(pointer, length, capacity, access);
         }
 
         [CLSCompliant(false)]
         protected unsafe void Initialize(byte* pointer, long length, long capacity, FileAccess access) 
         {
-            Initialize(pointer, length, capacity, access, false);
-        }
-
-        internal unsafe void Initialize(byte* pointer, long length, long capacity, FileAccess access, bool skipSecurityCheck) 
-        {
             if (pointer == null)
                 throw new ArgumentNullException(nameof(pointer));
             if (length < 0 || capacity < 0)
@@ -221,12 +191,6 @@ namespace System.IO {
             if (_isOpen)
                 throw new InvalidOperationException(Environment.GetResourceString("InvalidOperation_CalledTwice"));
 
-            if (!skipSecurityCheck) {
-#pragma warning disable 618
-                new SecurityPermission(SecurityPermissionFlag.UnmanagedCode).Demand();
-#pragma warning restore 618
-            }
-
             _mem = pointer;
             _offset = 0;
             _length = length;
@@ -265,7 +229,6 @@ namespace System.IO {
             if (!_isOpen) __Error.StreamIsClosed();
         }
         
-        [ComVisible(false)] 
         public override Task FlushAsync(CancellationToken cancellationToken) { 
         
             if (cancellationToken.IsCancellationRequested) 
@@ -421,7 +384,6 @@ namespace System.IO {
             return nInt;
         }
         
-        [ComVisible(false)]
         public override Task<Int32> ReadAsync(Byte[] buffer, Int32 offset, Int32 count, CancellationToken cancellationToken) {        
             if (buffer==null)
                 throw new ArgumentNullException(nameof(buffer), Environment.GetResourceString("ArgumentNull_Buffer"));
@@ -618,7 +580,6 @@ namespace System.IO {
             return;
         }
         
-        [ComVisible(false)] 
         public override Task WriteAsync(Byte[] buffer, Int32 offset, Int32 count, CancellationToken cancellationToken) { 
         
             if (buffer==null)
diff --git a/src/mscorlib/src/System/IO/UnmanagedMemoryStreamWrapper.cs b/src/mscorlib/src/System/IO/UnmanagedMemoryStreamWrapper.cs
index 040ddbb3d7..99b257ea56 100644
--- a/src/mscorlib/src/System/IO/UnmanagedMemoryStreamWrapper.cs
+++ b/src/mscorlib/src/System/IO/UnmanagedMemoryStreamWrapper.cs
@@ -13,7 +13,6 @@
 
 using System;
 using System.Runtime.InteropServices;
-using System.Security.Permissions;
 using System.Diagnostics.CodeAnalysis;
 using System.Diagnostics.Contracts;
 using System.Threading;
diff --git a/src/mscorlib/src/System/IO/__Error.cs b/src/mscorlib/src/System/IO/__Error.cs
index ad4972de54..955ddbec63 100644
--- a/src/mscorlib/src/System/IO/__Error.cs
+++ b/src/mscorlib/src/System/IO/__Error.cs
@@ -21,7 +21,6 @@ using Win32Native = Microsoft.Win32.Win32Native;
 using System.Text;
 using System.Globalization;
 using System.Security;
-using System.Security.Permissions;
 using System.Diagnostics.Contracts;
 
 namespace System.IO {
@@ -51,10 +50,6 @@ namespace System.IO {
         internal static void ReadNotSupported() {
             throw new NotSupportedException(Environment.GetResourceString("NotSupported_UnreadableStream"));
         }
-    
-        internal static void SeekNotSupported() {
-            throw new NotSupportedException(Environment.GetResourceString("NotSupported_UnseekableStream"));
-        }
 
         internal static void WrongAsyncResult() {
             throw new ArgumentException(Environment.GetResourceString("Arg_WrongAsyncResult"));
@@ -187,34 +182,11 @@ namespace System.IO {
                 throw new IOException(Win32Native.GetMessage(errorCode), Win32Native.MakeHRFromErrorCode(errorCode), maybeFullPath);
             }
         }
-
-        // An alternative to WinIOError with friendlier messages for drives
-        internal static void WinIODriveError(String driveName) {
-            int errorCode = Marshal.GetLastWin32Error();
-            WinIODriveError(driveName, errorCode);
-        }
-
-        internal static void WinIODriveError(String driveName, int errorCode)
-        {
-            switch (errorCode) {
-            case Win32Native.ERROR_PATH_NOT_FOUND:
-            case Win32Native.ERROR_INVALID_DRIVE:
-                throw new DriveNotFoundException(Environment.GetResourceString("IO.DriveNotFound_Drive", driveName));
-
-            default: 
-                WinIOError(errorCode, driveName);                
-                break;
-            }
-        }
     
         internal static void WriteNotSupported() {
             throw new NotSupportedException(Environment.GetResourceString("NotSupported_UnwritableStream"));
         }
 
-        internal static void WriterClosed() {
-            throw new ObjectDisposedException(null, Environment.GetResourceString("ObjectDisposed_WriterClosed"));
-        }
-
         // From WinError.h
         internal const int ERROR_FILE_NOT_FOUND = Win32Native.ERROR_FILE_NOT_FOUND;
         internal const int ERROR_PATH_NOT_FOUND = Win32Native.ERROR_PATH_NOT_FOUND;