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Definition: FAT


(File Allocation Table) The file system used for compatibility. Developed for floppy disks in the late 1970s, FAT was the primary file system for hard drives in DOS and Windows prior to NTFS. FAT is also used for digital camera storage. See file system and NTFS.

Today, FAT32 and exFAT are widely used for USB and external storage drives because they are supported by all major platforms, including Windows, Mac, Linux and mobile devices. See USB drive.

FAT Directory and Table
The FAT directory maintains a list of file names and dates, and the FAT table has an entry for each drive cluster. When a drive is high-level formatted, the FAT table is recorded twice.

The directory points to an entry in the table where the file starts. If the file is larger than one cluster, the first table entry points to the next cluster and so on until the end of file (see below). If a cluster becomes damaged, it is marked as such and never used again. See FAT32 and cluster.




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