File Allocation Table (FAT) is a file system developed for personal computers and was the default file system for the DOS and Windows 9x operating systems. Originally developed in 1977 for use on floppy disks, it was adapted for use on hard disks and other devices. The increase in disk drive capacity over time drove modifications to the design that resulted in new versions: FAT12, FAT16, FAT32, and exFAT.