The following applies to the NEC D765AC-2 and was found through testing:
* The index mark pre-amble, syncs and mark are not required. If this area is filled with 0x04e the FDC will still read the sectors.
* The only address mark which identifies the ID field is 0x0fe. Attempting to use any other mark for an ID field will result in the ID field being ignored.
* The only data marks which identify the data field are 0x0fb (Data) and 0x0f8 (Deleted Data). Attempting to use any other mark for a data field will result in the field being ignored.