60. file system

• What is the FAT? What does it do? How many FATs are there?

  • A FAT is the file allocation table.

  • The FAT contains one entry for every addressable cluster on the drive.

  • FAT entry indicates whether the cluster is allocated or unallocated.

  • If the cluster is in allocated space, the entry indicates where the cluster is in a file's cluster chain.

  • File cluster chain is made of numeric pointers (cluster numbers) of each cluster in the file. Last pointer in the chain indicates the last cluster: 0xFFF.

  • FAT file systems employ two FAT tables on the drive.