It was made part of the resident ROM of the Amiga, Kickstart, with the release of AmigaOS 2.0, allowing the Amiga to boot from from floppy disks in this format. It was possible since AmigaOS 1.3 to boot from a hard drive in this format, because Amiga hard disks stored a Rigid Disk Block including a full copy of the filesystem handling code on the hard disk.
Its main difference in comparison to OFS is that it used all 512 bytes of data block for data. OFS stored only 488 bytes of data in each data block.
With AmigaOS 2.1 and 3.0 came two special "modes" of FFS:
- International mode
- AmigaDOS filenames are case-preserving but case-insensitive. DF0:FOO/BAR accesses the same file as DF0:foo/bar. However, this behavior didn't extend to ISO-8859-1 characters outside the ASCII range. International mode extends this so that DF0:FÖÖ/BÅR accesses the same file as DF0:föö/bår
- Directory Caching mode
- extra blocks were used to store files in a directory and their metadata, rather than having to fetch every file header block referenced by the directory block and collate the results. This lead to far fewer disk reads when browsing a disk, but slowed other operations like creating, deleting, renaming or modifying files.
Floppy disks can be distinguished between OFS and FFS by the first four bytes of their bootblock, which is the first two sectors of the disk.
|"DOS\2"||OFS with International mode|
|"DOS\3"||FFS with International mode|
|"DOS\4"||OFS with International and Directory Caching mode|
|"DOS\5"||FFS with International and Directory Caching mode|