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I have a floppy. It was storing names in 8.3 form I renamed one of the files to 20.3 on Windows xp and opened it on linux both acknoledge that name .Please tell me what is the file system. I thought it had to be FAT 12 even the boot sector BPB tells this. Please tell me about the directory specification of this FAT and all stuff. Goolge doesnt help. I have tried it . I would be really grateful if soemone could help please!

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As pointed out, what you saw is the VFAT long‑filename extension layered on top of FAT12. The BPB still reports FAT12 because VFAT is not a different on‑disk format — it simply uses extra 32‑byte directory entries to hold Unicode long names while leaving the original 8.3 short entry in place (so DOS/older tools still work).

How it is stored (brief, accurate): directories are arrays of 32‑byte entries. Long names are split into special entries with the attribute byte set to 0x0F; each such entry holds up to 13 16‑bit characters (UCS‑2/UTF‑16LE), a sequence number, and a checksum that ties the LFN entries to the following 8.3 entry. The LFN entries appear immediately before the corresponding short entry. Windows (XP) and the Linux vfat driver reconstruct those entries at mount time, which is why both OSes show your 20.3 name even though the BPB says FAT12.

Quick verification workflow (non‑destructive):

  • Make an image copy: sudo dd if=/dev/fd0 of=floppy.img bs=512 count=2880 (adjust count for other floppy sizes).
  • Mount read‑only to inspect: sudo mount -o ro,loop -t vfat floppy.img /mnt then ls -la /mnt.
  • To see raw directory entries, use a hex viewer on the image (look for attribute 0x0F in the 11th byte of 32‑byte records and the 8.3 short entry that follows). Do all work on the image to avoid corrupting the original disk.

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Member Avatar for jbennet

its VFAT

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