FAT, an acronym for File Allocation Table, was introduced back in 1981 for use on all Intel platform operating systems. FAT keeps track of all files in a partition. Each cluster has an entry in the FAT that indicates if that cluster has any current data in it. The root directory contains file and disk entries that point to the remaining files located on the disk. The root directory immediately follows the FAT.

The FAT file system is very simple, and it has no corruption prevention methods like NTFS or HPFS.

When Windows 95 was released, it had an updated form of FAT called VFAT. VFAT allowed 255 character filenames with embedded spaces, multiple periods and case preservation. The old FAT was restricted to the old 8.3 format, or 8 characters, a period, and a 3 character file extension. VFAT also creates a directory that is readable by FAT-era devices.