Source: FD 179X-01 Floppy Disk Formatter/Controller Family

IBM 3740 FORMAT

Track
        Index  Sector 
        Mark 
40x  6x                247x
FF   00  FC     ..     FF

Sector
              0      1      2       3    4 5
         IDAM Track  Side   Sector  ENC  IDAM           DAM   Data Data
              Number Number Number       CRC                       CRC
26x  6x                                   2x    11x  6x             2x
FF   00  FE   tn     sin    sen     00   icrc   FF   00  FB   ..   crc   


IBM SYSTEM 34 FORMAT

Track
            Index  Sector
            Mark
80x 12x 3x                 598x
4E  00  F6  FC      ..     4E

Sector
               0      1      2      3    4 5
         IDAM  Track  Side   Sector ENC  IDAM               DAM  Data Data
               Number Number Number      CRC                          CRC
12x  3x                                  2x    22x 12x  3x            2x   54x
00   F5  FE    tn     sin    sen    01   F7    4E  00   F5  FB   ..   crc  4E