File Allocation Table

file allocation table

[‚fīl ‚al·ə′kā·shən ‚tā·bəl] (computer science) A table stored on hard or removable disks used to locate files or sections of files if scattered about the disk. Abbreviated FAT.

File Allocation Table

(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 ofwhich can be one or more sectors, depending on the size ofthe partition. Each cluster is either allocated to a file ordirectory or it is free (unused). A directory lists the name,size, modification time and starting cluster of each file orsubdirectory it contains.

At the start of the partition is a table (the FAT) with oneentry for each cluster. Each entry gives the number of thenext cluster in the same file or a special value for "notallocated" or a special value for "this is the last cluster inthe chain". The first few clusters after the FAT contain theroot directory.

The FAT file system was originally created for the CP/Moperating system where files were catalogued using 8-bitaddressing. 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 thatallowed partitions of up to 2 gigabytes.

Microsoft later created FAT32 to support partitions largerthan two gigabytes and pathnames greater that 256characters. It also allows more efficient use of disk spacesince clusters are four kilobytes rather than 32 kilobytes.FAT32 was first available in OEM Service Release 2 ofWindows 95 in 1996. It is not fully backward compatiblewith the 16-bit and 8-bit FATs.

IDG article.http://home.c2i.net/tkjoerne/os/fat.htm.http://teleport.com/~brainy/.http://209.67.75.168/hardware/fatgen.htm.http://support.microsoft.com/support/kb/articles/q154/9/97.asp.

Compare: NTFS.

file allocation table

File Allocation Table