Hi Joe This would explain why I can't read other tracks but doesn't explain why I can only read the first sector of track 0. When I get a chance, I'll put a scope to the signals to see if it also has some changes in sector length or something. The 96 does match to the 80 track drives as 96 tpi. This does make sense. I don't really know if it actually read the first sector completely correct though. It may have read the data and then failed the checksum, if the sector data was twice as long, it would still read the first 256 bytes correctly. Putting one scope channel on the sync output and the other on the data should make it clearer what they are. Having double length sectors would make sense with twice the tracks. This would require less modifications to HDOS in things like directories. Dwight disks. I don't know but I'm guessing that the HK normally used 40 track disks but that those disks came from someone had a mod to use 80 track disks. That was pretty common on a lot of the early computers. I did that to my Sanyo and I had a Kaypro that had the Advent Turbo ROM and 80 track drives installed.