It and its predecessors have been included in hundreds of commercial embedded applications. The FAT is a structure on a disk that maps the blocks of disk space occupied by individual files on that disk. These blocks are called clusters. A cluster is a group of sectors, which is the smallest addressable units of a disk. Sectors are 512 bytes in size.
Files typically contain many clusters.
FAT entries are in the same order as physical clusters on the disk and correspond one for one with them. A special value indicates the end of the file. The size of FAT entry dictates the size of the FAT and the maximum size of the disk. On a FAT12 disk, for example, each FAT entry is a 12-bit number. FAT12 is used for small media such as floppy disks.