The support for ATARI ST formats is mainly aimed at users of emulators. As far as I can tell, the .ST disk image format is a plain sector-by-sector image and requires no special support.

3.3.1. The GEMDOS File System

The file system implemented by the GEMDOS layer of the TOS operating system is actually FAT12/FAT16 as defined by MS-DOS, see Section 3.7.1, “FAT12, FAT16, and FAT32”.

There are some slight differences. GEMDOS uses the "system identifier" field to store a serial number, used to detect floppy changing. For booting, a different branch instruction is used, and the boot sector must have a checksum of $1234 (computed from 16-bit words in big-endian byte order), instead of the $55AA marker. GEMDOS does not support arbitrary numbers of sectors per cluster and instead emulates larger sector sizes (1K, 2K, 4K) if it runs out of cluster numbers. disktype will report the boot checksum and the unusual sector sizes, if found. Otherwise, the volume will report as FAT12 or FAT16 as appropriate.

3.3.2. The ATARI ST (AHDI) Partitioning Scheme

The ATARI ST has its own parititioning scheme for hard disks, although it is structurally very similar to the PC partition table format. The first sector of the disk contains boot code as well as four partition entry slots. If more than four partitions are required, one of the four primary slots is used for an "extended" partition, which contains a linked list of partition map sectors using the same layout.

Each partition has a type code of three characters, which disktype displays in plain. The three codes used by the AHDI hard disk driver are recognized.