Definition: FAT

(File Allocation Table) The mechanism that keeps track of files stored on disk in the FAT file system, which originated in DOS and was used in Windows prior to the NTFS file system. However, the FAT32 format is widely used with external devices for compatibility on all platforms (see FAT32).

The FAT Table
When a disk is high-level formatted, the FAT table is recorded twice and contains an entry for each cluster on the disk. The file system's directory list, which contains file name, extension, date, etc., points to the FAT entry where the file starts.

If a file is larger than one cluster, the first FAT entry points to the next FAT entry where the second cluster of the file is stored and so on to the end of the file. If a cluster becomes damaged, its FAT entry is marked as such, and that cluster is never used again. The original 16-bit version of (FAT16) supported hard disk partitions up to 4GB and files as large as 2GB. The 32-bit version dramatically increased capacity. See FAT32, NTFS, inode and file system.

The FAT Table

The file RESUME.DOC is stored in clusters 0, 2, 3 and 7. The directory entry points to cluster 0 where the file begins. The entry for cluster 0 points to cluster 2 and so on. BUDGET.XLS is stored in clusters 1, 4, 8 and 9.