file allocation table

file allocation table
    n 1: the part 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)
    

File Allocation Table
FAT
FAT32

   <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://idg.net/idgframes/english/content.cgi?vc=docid_9-62525.html).
   (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}.

   [How big is a FAT?  Is the term used outside MS DOS?  How long
   is a FAT16 filename?]

   (2000-02-05)