High Quality Content by WIKIPEDIA articles! The Amiga Fast File System (FFS; not to be confused with the identically named Berkeley Unix FFS) is a file system used on the Amiga personal computer. The previous Amiga filesystem (known originally simply as "DOS" or AmigaDOS) upon the release of FFS became known as Amiga Old File System (OFS). OFS, while fine on floppy disk, soon proved too slow to keep up with era hard drives. FFS was designed as a full replacement for the original Amiga filesystem.