File Allocation Table

The File Allocation Table is a disk data structure that records which clusters are free, occupied, or linked to the next cluster in a file or directory.

Cluster (file systems): A cluster is the smallest allocation unit a file system assigns to a file. FAT entries track these allocation units rather than individual disk sectors.
Sector (disk): A sector is a fixed-size addressable unit of storage on a disk. FAT clusters group sectors into the larger units whose allocation the table records.
Inode: An inode is a Unix-like file-system record containing metadata and references to a file’s data blocks. Unlike FAT’s volume-wide link table, inodes hold allocation references alongside each file’s metadata.
FAT12: FAT12 is a FAT file-system variant that uses 12-bit allocation entries. Its compact entries suited early floppy disks with relatively few clusters.
File Allocation Table entry: A File Allocation Table entry records a cluster’s allocation state or the next cluster in a chain. A file’s contents are followed by interpreting entries as links, end markers, or free-space markers.
Volume (computing): A volume is a logical storage area formatted with a file system. A FAT describes cluster allocation within a particular formatted volume.
NTFS: NTFS is a journaling file system developed by Microsoft for Windows. NTFS uses the Master File Table rather than a FAT cluster-link table.
FAT16: FAT16 is a FAT file-system variant that uses 16-bit allocation entries. It expanded the addressable cluster range beyond FAT12 for larger storage volumes.
Directory entry (file systems): A directory entry stores a file or directory’s name and metadata, including its starting cluster in FAT. The starting cluster in this record provides the first link into a file’s FAT chain.
Little-endian: Little-endian is a byte order that stores the least significant byte of a value first. FAT variants encode multi-byte table entries using little-endian byte order.

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