The OS/2 FAT file system is based on the DOS FAT file system. This file system, also used in previous releases of the OS/2 operating system and in PC-DOS, controls storage of data files for hard and floppy disks.

The FAT file system is hierarchical, supporting multiple directories on the disk. Each directory can contain one or more files or subdirectories.

The FAT file system uses the 8.3 file name convention. Under this convention, the file name consists of a file name of up to eight characters, a separating period (.), and a file name extension of up to three characters.