File Allocation Table (FAT)

The File Allocation Table filesystem family tracks file storage through a table indexed by allocation cluster. A file's directory entry points to its first cluster; table entries link later clusters or mark the end of its chain. Following that chain reconstructs a fragmented file. This simple organization differs from an extent tree that describes long contiguous runs at once. FAT variants differ in entry widths and other layout rules. File length and cluster-chain traversal must agree with the on-disk metadata; the file's bytes do not necessarily occupy one contiguous interval.

// Target: computer-science.bigb

FAT32 is a File Allocation Table filesystem variant using 32-bit table entries with fewer bits available for cluster numbers. A directory entry stores file size in a 32-bit unsigned field, limiting one ordinary file to $2^{32}-1$ bytes. This limit is distinct from a volume's capacity, which also depends on sector and cluster layout and implementation restrictions. FAT32 is widely interoperable but lacks native per-file security ACLs and metadata journaling of the kind provided by NTFS. Filesystem limits should be distinguished from a formatting tool's additional limits.^[ref]

// Target: computer-science.bigb