10 Facts About FAT BPB

1.

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

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2.

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

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3.

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 BPB 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.

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4.

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

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5.

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

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Windows 9x DOS
6.

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

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7.

Originally, the FAT BPB 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.

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8.

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

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9.

The entry for cluster 0 at the beginning of the FAT 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.

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10.

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

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