I didn't see a few things mentioned in this thread, which may be in the books, but not yet on the list. the disk controller attempted to invent soft sector disks, that is format disks without using the hardware sector markers, or the index mark. It did this all in software. If you have a hardware index mark, you always know where to start counting to calculate the same spot on the track every revolution. Without that you have to have headers written for every sector, and read headers and calculate the sector number before the data starts if the sector is the desired one. This calls for higher performance hardware or firmware than one needs to have with just hard sectoring. Also, there is something that becomes a monster with the hard drives of long ago, which had what was called RF coming up the cable, not data bits, called the write splice, or write problem. old disk drives had various schemes to do seeking, from track to track, but saved a lot of money by only doing a serial data stream to and from the heads (with some restrictions). If you are doing soft sectoring, you have to put your controller logic in the mode to be reading the rf from the drive to sending it in a hurry when your header ended to write the sector. The apple 2 disks could use any type of 5 1/4" media without anything but the format written on it by the formatting program. Remember a lot of media companies tried to jack up the price of goods by having special preformatted disks, and so did the vendors around the time that the apple ][ came into existance. It was a good thing that the apple people at least didnt do this initially, though they learned to do so with hard drives, and continue to this day to make it difficult to use anything but their own drives with system. Jmi "Cini, Richard" wrote: