MS-DOS file system - late 1970s (8 bit version for 8080 cpu) - current.
  Wikipeia topic : file access table.  

  Also called the FAT file system because 
    its primary feature is its file allocation table (FAT).

  Although it is technically a Microsoft OS filesystem, its simplicity and
    public protocol made it ideal for devices that need to be accessed by
    a variety of OSes. So, common on flash drives <= 8GB.

  The FAT consists of 
    Table with an entry for every cluster on the storage partition.
    * Cluster represent a single unit of access on storage device consisting
      of one or more sectors. Determined by version of FAT, actual partition
      size and user's choice. 

    Size of entry based on version of FAT (8,12,16,32 bit).

    Entry indicats : available cluster, location of next cluster(entry) if 
      being used by a file, or end of file cluster.

    Example

  Designed to protect against loss of data if FAT update fails.
    Implemented as a pair of tables stored at two locations on a partition
    and kept synchronized.

  Each storage block (cluster) on partition numbered sequentially.
    Actual access of block may be LBA or CHS depending on OS/hardware.

  One FAT entry for each cluster.