Intel DD format differences

From: Eric Smith <eric_at_brouhaha.com>
Date: Tue Feb 22 15:15:27 2005

Steve Thatcher wrote about Intel double density (M2FM) disk format:
> I referred to the 1793 technical spec that outlined what the 3740 and
> system 34 formats are. Those manuals are also out on bitsavers under
> Western Digital. I saw no reference to PLO sync bytes or the special gap
> bytes in the SD format.

The gaps (PLO sync) and marks look different to me:


                IBM 3740 (FM) IBM System 34 (MFM) Intel DD (M2FM)

gap 1: 40 * 00 or FF 80 * 4E 46 * ??
                 6 * 00 12 * 00

index mark: 1 * FC (Ind Mk) 3 * C2 1 * 0C
                                     1 * FC

gap 2: 26 * 00 or FF 50 * 4E 18 * 00
                 6 * 00 12 * 00 10 * FF

addr mark: 1 * FE (IDAM) 3 * A1 1 * 0E
                                     1 * FE

                 1 * trk num 1 * trk num 1 * trk num
                 1 * 00 (side num) 1 * side num 1 * 00
                 1 * sector num 1 * sector num 1 * sector num
                 1 * 00 (sect len) 1 * sector len 1 * 00
                 2 * CRC 2 * CRC 2 * CRC

gap 3: 11 * 00 or FF 22 * 4E 2 * 00
                 6 * 00 12 * 00 10 * FF

data mark: 1 * FB (DAM) 3 * A1 1 * 0B
                                     1 * FB
               128 * data 256 * data 256 * data
                 2 * CRC 2 * CRC 3 * CRC

gap 4: ~247 * 00 or FF ~598 * 4E ? * ??
Received on Tue Feb 22 2005 - 15:15:27 GMT