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File Allocation Table

File Allocation Table

(also FAT, FAT16)

File Allocation Table definition

File allocation table (also known as FAT) is a file system developed for hard drives by Microsoft. Operating systems use it to manage hard drive files. The FAT system uses a table to track the clusters on a storage volume and how those clusters link together through associated directories and files. The table plays a vital role in file storage and allocation. The acronym (FAT) refers to the file system but can sometimes refer to the table itself.

How FAT systems work

  • The FAT system creates an index table of the files stored on the device or in the system.
  • The index table contains an entry for each data cluster (data storage area).
  • The entries contain the number of the next cluster, a marker indicating EOF (end of file), unused disk space, or other specially reserved areas in the drive.
  • The operating system (OS) looks up the cluster number of each successive part of the file until it reaches the end of it.

Technical details

  • File allocation tables are typically located on a disk’s first sector (disk sector 0).
  • There are three major variants of file allocation tables: FAT12, FAT16, and FAT32.
  • FAT supports volume sizes of up to 4GB.
  • File allocation tables don’t provide any file system security.

Where FAT systems are used

  • USB memory sticks
  • Memory cards
  • Digital cameras
  • Portable devices

Further reading

Ultimate digital security