FAT stands for File Allocation Table. Name given to an MS-DOS file system component that identifies files, directories, and free space on disk.

A disk is divided into partitions. Under the FAT file system, each partition is divided into clusters, each of which can be one or more sectors, depending on the size of the partition. Each cluster is either allocated to a file or directory or not used. A directory lists the name, size, modification time, and starting set of each file or subdirectory it contains.

FAT is very similar to an operating system-generated roadmap for finding data associated with a particular file. References in FAT act as pointers and point to sets by numeric reference.