FAT (File Allocation Table)

The FAT filesystem uses an index table stored on the device to identify chains of data storage that are associated with a single file.

  • the table is a linked list of entries for each cluster
    - a cluster is an atomic unit of space on a hard disk that can be allocated to hold files.
    	- Storing small files on a filesystem with large clusters will therefore waste disk space (slack space)
    - being a linked list, each entry contains either the number of the next cluster in the file, or else a marker indicating the end of the file, unused disk space, or special reserved areas of the disk.
    	- also, the root directory of the disk contains the number of the first cluster of each file in that directory
    	- this enables the operating system to traverse the FAT, looking up the cluster number of each successive part of the disk file as a cluster chain until the end of the file is reached
    	- Sub-directories are implemented as special files containing the directory entries of their respective files.
    FAT is a legacy system, and is supported for backward-compatability reasons