Atari ST disk images

Drop an .ST or .MSA image on the page (or use Open). Nothing is uploaded; the image is read in your browser.

Disk summary shows the BIOS parameter block (bytes per sector, sectors per cluster, FAT size, root entries, media byte), the geometry, the volume label, free space, and whether the boot sector is executable.
The cluster map colours each cluster as free, used, or bad. Files lists the whole tree; click a file to see its contents as text or hex. .PRG, .TOS, .TTP, .APP, and .ACC files also show their GEMDOS program header and the symbol table if there is one.
Extract all downloads every file as a ZIP that keeps the folder structure.
Download .ST / Download .MSA convert between the two formats.
New blank disk makes a formatted single- or double-sided image with 9, 10, or 11 sectors per track and 80–82 tracks. Add files copies files into the root directory.

Format notes

.ST is a raw sector dump in the order track 0 side 0, track 0 side 1, track 1 side 0, … The geometry is taken from the BPB, falling back to a guess from the file size.
.MSA (Magic Shadow Archiver) has a 10-byte big-endian header — $0E0F, sectors per track, sides − 1, first and last track — then each track as a length word and data. A track is run-length encoded ($E5 byte count.w) when that is shorter.
The boot sector is executable when its 256 big-endian words sum to $1234.
The file system is FAT12 with MS-DOS–style 8.3 directory entries; long file names do not exist on TOS.

Limitations: files can only be added to the root directory; deleting files and copy-protected or non-standard track layouts (e.g. .STX) are not supported.

Pasti .STX images (copy-protected disks recorded with their track timing and weak bits) are recognised but not opened: they aren’t plain sectors. Use an emulator with Pasti support, such as Hatari or Steem. See also Kickstart and TOS ROM identifier.

Works with

Format notes