11 Facts About FAT ID

FAT ID file system is a legacy file system which is simple and robust.

Originally designed in 1977 for use on floppy disks, FAT ID was adapted and used almost universally on hard disks throughout the DOS and Windows 9x eras for two decades.

The root directory of the disk contains the number of the first cluster of each file in that directory; the operating system can then traverse the FAT ID table, 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.

The successive major versions of the FAT ID format are named after the number of table element bits: 12,16, and 32.

The FAT ID standard has been expanded in other ways while generally preserving backward compatibility with existing software.

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FAT ID uses little-endian format for all entries in the header and the FAT ID.

ExFAT ID BPBs are located at sector offset to, overlapping all the remaining entries of a standard FAT ID32 EBPB including this one.

Originally, the FAT ID was meant to be a bit flag with all bits set except for bit 2 cleared to indicate an 80 track format, bit 1 cleared to indicate a 9 sector format, and bit 0 cleared to indicate a single-sided format, but this scheme was not followed by all OEMs and became obsolete with the introduction of hard disks and high-density formats.

The remaining 4 bits in the 32-bit FAT ID entry are usually zero, but are reserved and should be left untouched.

The entry for cluster 0 at the beginning of the FAT ID must be identical to the media descriptor byte found in the BPB, whereas the entry for cluster 1 reflects the end-of-chain value used by the formatter for cluster chains.

Older versions of DOS could mistake LFN names in the root directory for the volume label, VFAT ID was designed to create a blank volume label in the root directory before adding any LFN name entries.