I am searching for the answer, what is the theoretical minimum size for a FAT12 volume?

There is only requirements that embedded and normal systems should recognize it on a pen drive as legal file system. Small size as possible without filesystem driver crash. Even if only 1 data sector - that will be perfect! So what is the minimum legal size?

Thank You,


mkfs.vfat, if you limit it to one FAT (-f 1) and 16 root directory entries (-r 16), still insists on a minimum of 33792 bytes (66 sectors × 512 bytes), although it uses only 10 sectors for the filesystem (56 sectors remain for data).

The filesystem remains mountable if you truncate it to 10 sectors, although attempting to write to such a truncated fs will result in the filesystem driver complaining.

You might have some luck with adjusting the filesystem structures with a hex editor, to properly shrink it to around 11 sectors...

  • Thx, i will try those parameters. – Andrew_ww May 18 '13 at 18:26
  • grawity: could you tell me plz your media descriptor byte value for 66 sector volume? You can find that 8 bit value in boot record at offset 0x15. I have installed an ms-dos 6.22 under virtualbox for test purposes, and anything i try, ms-dos always ignores everything because of media descriptor byte. – Andrew_ww May 18 '13 at 23:21
  • @Andrew_ww: I haven't tested it with MS-DOS. – user1686 May 19 '13 at 10:35

Minimum working system (on windows and mac os) with 1Kb of free space

is 7 sectors x 512bytes = 3.5Kb

1 sector - boot sector

2 sectors - fat1 + fat2 tables

2 sectors - root directory (32 entries)

2 sectors - at least one cluster of data

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