MfsReader 1.0.0

MfsReader

A lightweight .NET library for reading classic Macintosh File System (MFS) disk images and extracting their contents. MFS was the original file system used by early Macintosh computers (1984-1985) before being replaced by HFS.

Features

• Read MFS disk images (e.g., 400K floppy disk images)
• Enumerate all files in an MFS volume
• Extract both data and resource forks from files
• Access file metadata (name, type, creator, dates, sizes)
• Support for .NET 9.0
• Zero external dependencies

Installation

Add the project reference to your .NET application:

dotnet add reference path/to/MfsReader.csproj

Or, if published on NuGet:

dotnet add package MfsReader

Usage

Reading an MFS Disk Image

using MfsReader;

// Open a disk image file
using var stream = File.OpenRead("mfs400K.dsk");

// Create an MFS volume reader
var volume = new MFSVolume(stream);

// Get volume information
var mdb = volume.MasterDirectoryBlock;
Console.WriteLine($"Volume Name: {mdb.VolumeName}");
Console.WriteLine($"Created: {mdb.CreationDate}");
Console.WriteLine($"Last Backup: {mdb.LastBackupDate}");

Enumerating Files

// Get all files in the volume
var files = volume.GetEntries();

foreach (var file in files)
{
    Console.WriteLine($"File: {file.Name}");
    Console.WriteLine($"  Type: {file.FileType}");
    Console.WriteLine($"  Creator: {file.Creator}");
    Console.WriteLine($"  Data Fork: {file.DataForkSize} bytes");
    Console.WriteLine($"  Resource Fork: {file.ResourceForkSize} bytes");
    Console.WriteLine($"  Created: {file.CreationDate}");
    Console.WriteLine($"  Modified: {file.LastModificationDate}");
}

Extracting File Data

// Extract data fork
foreach (var file in volume.GetEntries())
{
    // Get data fork as byte array
    byte[] dataFork = volume.GetDataForkData(file);
    File.WriteAllBytes($"{file.Name}.data", dataFork);
    
    // Get resource fork as byte array
    byte[] resourceFork = volume.GetResourceForkData(file);
    File.WriteAllBytes($"{file.Name}.rsrc", resourceFork);
}

Streaming File Data

// Stream file data to an output stream
var file = volume.GetEntries().First();

using var outputStream = File.Create("output.bin");
volume.GetDataForkData(file, outputStream);

API Overview

MFSVolume

The main class for reading MFS volumes.

• MFSVolume(Stream stream) - Opens an MFS volume from a stream
• MasterDirectoryBlock - Gets the master directory block (volume metadata)
• AllocationBlockMap - Gets the allocation block map of the volume
• GetEntries() - Enumerates all file entries in the volume
• GetDataForkData(file) - Reads the data fork as a byte array
• GetDataForkData(file, outputStream) - Streams the data fork to an output stream
• GetResourceForkData(file) - Reads the resource fork as a byte array
• GetResourceForkData(file, outputStream) - Streams the resource fork to an output stream
• GetFileData(file, forkType) - Reads file data as a byte array
• GetFileData(file, outputStream, forkType) - Streams file data to an output stream

MFSMasterDirectoryBlock

Contains volume-level metadata:

• Signature - Volume signature (0xD2D7 for MFS)
• VolumeName - Name of the volume
• CreationDate - Volume creation date
• LastBackupDate - Volume last backup date
• Attributes - Volume attributes/flags
• NumberOfFiles - Number of files in the volume
• FileDirectoryStart - Starting sector of the file directory
• FileDirectoryLength - Length of the file directory in sectors
• NumberOfAllocationBlocks - Number of allocation blocks on the volume
• AllocationBlockSize - Size of allocation blocks in bytes
• ClumpSize - Clump size in bytes
• AllocationBlockStart - Starting sector of the first allocation block
• NextFileNumber - Next file number to be assigned
• FreeAllocationBlocks - Number of free allocation blocks

MFSFileDirectoryBlock

Represents a file entry in the MFS volume:

• Name - File name (up to 255 characters)
• Flags - Entry flags (used, locked)
• Version - Version number
• FileType - Four-character file type code
• Creator - Four-character creator code
• FinderFlags - Finder flags
• ParentLocationX - X-coordinate of file's location in parent
• ParentLocationY - Y-coordinate of file's location in parent
• FolderNumber - Folder number
• FileNumber - File number
• CreationDate - File creation date
• LastModificationDate - File last modified date
• DataForkAllocationBlock - Starting allocation block for data fork
• DataForkSize - Size of the data fork in bytes
• DataForkAllocatedSize - Allocated size of the data fork in bytes
• ResourceForkAllocationBlock - Starting allocation block for resource fork
• ResourceForkSize - Size of the resource fork in bytes
• ResourceForkAllocatedSize - Allocated size of the resource fork in bytes

Building

Build the project using the .NET SDK:

dotnet build

Run tests:

dotnet test

MFSDumper CLI

Extract an MFS disk image to a directory using the dumper tool.

Install/Build

dotnet build dumper/MFSDumper.csproj -c Release

Usage

MFSDumper \
    /path/to/disk.dsk \
    -o /path/to/output \
    [--data-only | --resource-only]

• Input: Path to the .dsk image.
• Output: Destination directory for extracted files.
• Fork selection:
  • --data-only: Extract only data forks.
  • --resource-only: Extract only resource forks.

Files are written as <Name>.data and <Name>.res, with / and : replaced by _ for compatibility.

Requirements

• .NET 9.0 or later

License

MIT License. See LICENSE for details.

Copyright (c) 2026 Hugh Bellamy

About MFS

The Macintosh File System (MFS) was the original file system for the Macintosh computer, introduced in 1984. Key characteristics:

• Flat file structure (no subdirectories/folders)
• Support for data and resource forks
• Maximum of 128 files per volume
• Primarily used on 400K floppy disks
• Replaced by HFS (Hierarchical File System) in 1985

Related Projects

• HfsReader - Reader for HFS (Hierarchical File System) volumes