2

Based on the information I can see from this page:

  • FAT12 uses a maximum of 4086 clusters (2^12 - 10)
  • FAT16 uses 65526 (2^16 - 10)
  • FAT32 uses ~268435456 (2^28)

I understand that FAT32 uses 28 bits instead of 32 as 4 bits are reserved, but what about the discrepancy in the max number of clusters? Why do FAT12 and FAT16 have 10 less available clusters than they should do based on the number of bits available?

Are these clusters present but reserved for certain functionality? If so, what are they being used for?

VortixDev
  • 1,214

1 Answers1

3

Why do FAT12 and FAT16 have 10 less available clusters than they should do based on the number of bits available?

  1. First 2 values for cluster nums (0x0 and 0x1) are not available - the place for them in FAT table is used to store the FAT signature. First cluster number is 0x2.

  2. Last 8 values for cluster nums (0xff8..0xfff and 0xfff8..0xffff) are reserved for special marks (end of cluster chain, bad cluster, etc.)

Another values are available for cluster number coding.

Akina
  • 3,295