FAT 
file allocation table 
The FAT is the table, or record, of where a specific file is stored on a PC's (but not a Mac's) hard disk. Hard drive data is stored in small chunks called clusters. A particular file is made up of any number of these clusters, but the clusters might be located on different parts of the hard disk. The FAT keeps track of where each file's clusters are located and how they should be reassembled. The original FAT was introduced by Microsoft in 1983 for its MS-DOS operating system, but it has evolved since then to accommodate various changes in how files and clusters are managed; the latest version is FAT32. FAT is also supported by other operating systems, including Linux.