The disks do not have any of the needed marks recorded to sychronize to. Also the check byte is not a CRC of the type that any FDC uses. As to FM/MFM yes thats the same but that only defines what the bits sent by the serial stream are represented by on the magnetic media bot the next level up in the formatting of the data. To simplify, the NS* controller uses the holes to signify where data is rather than laying down a complex series of recorded marks to signal where the contrller where the disk is at. The result is that the controller hardware is simplified and the CPU can do some of the work. Correct. Allison