file allocation table

area of a disk on which the location of each file is recorded

File Allocation Table (FAT) is a partially patented file system developed by Microsoft for MS-DOS and was the primary file system for consumer versions of Microsoft Windows up to and including Windows Me. FAT as it applies to flexible/floppy and optical disk cartridges (FAT12 and FAT16 without long file name support) has been standardized as ECMA-107 and ISO/IEC 9293.
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Noun
1. the prt of a floppy disk or hard disk where information is stored about the location of each piece of information on the disk (and about the location of unusable areas of the disk)
(hypernym) table, tabular array

<file system> (FAT) The component of an MS-DOS or Windows 95 file system which describes the files, directories, and free space on a hard disk or floppy 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 it is free (unused). A directory lists the name, size, modification time and starting cluster of each file or subdirectory it contains.
At the start of the partition is a table (the FAT) with one entry for each cluster. Each entry gives the number of the next cluster in the same file or a special value for "not allocated" or a special value for "this is the last cluster in the chain". The first few clusters after the FAT contain the root directory.
The FAT file system was originally created for the CP/M[?] operating system where files were catalogued using 8-bit addressing. MS DOS's FAT allows only 8.3 filenames.
With the introduction of MS-DOS 4 an incompatible 16-bit FAT (FAT16) with 32-kilobyte clusters was introduced that allowed partitions of up to 2 gigabytes.
Microsoft later created FAT32 to support partitions larger than two gigabytes and pathnames greater that 256 characters. It also allows more efficient use of disk space since clusters are four kilobytes rather than 32 kilobytes. FAT32 was first available in OEM Service Release 2 of Windows 95 in 1996. It is not fully backward compatible with the 16-bit and 8-bit FATs.
IDG article. http://home.c2i.net/tkjoerne/os/fat.htm. http://www.teleport.com/~brainy/. http://209.67.75.168/hardware/fatgen.htm. http://support.microsoft.com/support/kb/articles/q154/9/97.asp.
Compare: NTFS.
[How big is a FAT? Is the term used outside MS DOS? How long is a FAT16 filename?]
(2000-02-05)