The Ultimate Guide to Atari ST Disk Images and Formats The Atari ST series, launched in 1985, revolutionized home computing with its built-in MIDI ports, crisp high-resolution graphics, and powerful 16-bit Motorola 68000 processor. Today, the vibrant Atari ST retrocomputing community relies heavily on disk images to preserve software, games, and applications. Because the Atari ST used standard 3.5-inch floppy disks but often employed custom formatting tricks for copy protection, several distinct disk image formats emerged.
Whether you are configuring an emulator like Hatari or Steem, or setting up modern hardware replacements like the Gotek floppy emulator, understanding these formats is essential. This guide breaks down every major Atari ST disk image format, explains how they differ, and shows you how to use them. Standard Data Formats: ST and MSA
The majority of software that did not feature heavy copy protection—such as public domain software, utilities, and cracked games—is stored in standard sector-dump formats. These formats capture the raw data of each sector sequentially. 1. .ST (Standard Disk Image)
The .ST format is the simplest and most widely supported Atari ST disk image type. It is a raw, uncompressed sector-by-sector copy of a floppy disk.
How it works: It contains no header information or metadata. It simply dumps the data starting from Track 0, Side 0, Sector 1 straight to the end of the disk.
Compatibility: Because of its simplicity, almost every Atari ST emulator, utility, and hardware floppy emulator supports .ST files natively.
Limitation: It cannot store any copy-protection mechanisms or non-standard disk layouts. 2. .MSA (Magic Shadow Archiver)
The .MSA format originated on the actual Atari ST hardware as a native backup utility tool.
How it works: Unlike .ST files, .MSA files include a small header that describes the disk layout (number of tracks, sides, and sectors). Crucially, it supports basic Run-Length Encoding (RLE) compression to compress empty space or repeating data bytes on the disk.
Compatibility: Highly popular in the European demoscene and archiving communities. Most modern emulators read it natively.
Limitation: Like the .ST format, it only stores standard sector data and cannot handle advanced copy protection. Preservation and Copy-Protected Formats: STX and IPF
As games grew more commercially successful, developers implemented sophisticated copy-protection schemes. These schemes intentionally violated standard floppy disk rules—using variable track lengths, missing sector IDs, fuzzy bits, or modified gap sizes—to prevent users from duplicating disks using standard desktop software. Standard .ST or .MSA files cannot capture these anomalies. 3. .STX (Pasti / Atari Software Preservation)
The .STX format was created by Jorge Cwik as part of the “Pasti” preservation project. It was designed specifically to accurately emulate copy-protected Atari ST disks.
How it works: Instead of just dumping data sectors, .STX stores the precise timing information, structural layouts, and intentional disk errors generated by the Western Digital floppy disk controller (FDC) chips.
Compatibility: Widely supported by major emulators like Hatari and Steem SSE. However, due to its complexity, it is generally not supported by hardware floppy drive replacements like the Gotek.
Use Case: This is the go-to format if you want to play original, un-cracked commercial Atari ST games via software emulation. 4. .IPF (Interchangeable Preservation Format)
Developed by the Software Preservation Society (SPS), .IPF is a universal, platform-independent disk preservation format used for Atari ST, Amiga, and Amstrad CPC disks.
How it works: .IPF does not record what the floppy controller reads; instead, it records the physical properties of the magnetic flux transitions on the disk surface itself. This makes it an absolute, flawless digital replica of the original master disk.
Compatibility: Requires a specific plugin library (capsimg) to run in emulators like Hatari. It is highly valued for historical archiving. Specialized and Hard Disk Formats
Beyond floppy disks, the Atari ST ecosystem utilizes other specific file extensions for hard drives and specialized hardware. 5. .DIM (DiskIn MyM)
An older, secondary raw sector format similar to .ST, created by the FastCopy and DiskIn utilities on the Atari ST. It contains a 32-byte header before the raw data. It is rarely used today but occasionally found in older software archives. 6. .HDV / .IMG (Hard Disk Images)
When emulating an Atari ST hard drive (like an ACSI or SCSI Megafile drive), emulators use raw hard disk images. These files represent the entire partitioned hard drive structure, allowing users to install large suites of productivity software or hard-disk-patched game collections. Quick Reference: Which Format Should You Use?
For general emulation (Utilities, Applications, Cracks): Use .ST or .MSA. They are lightweight, fast, and universally compatible.
For original, un-cracked retail games in an emulator: Use .STX (Pasti).
For real Atari hardware via a Gotek drive (FlashFloppy): Convert your files to .ST or use .HFE (the native HxC Floppy Emulator format required by some hardware setups). Converting Between Formats
If you need to manage your collection, several modern tools make conversion seamless:
HxC Floppy Emulator Software: A powerful cross-platform tool that can convert between .ST, .MSA, .STX, and hardware-friendly formats like .HFE.
Atari ST Disk Image Manager (MSA Converter): A classic Windows utility designed specifically to convert, extract, and manipulate files inside .ST and .MSA images.
By understanding these formats, you can ensure that the rich history of the Atari ST remains accessible, functional, and preserved for decades to come.
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