Well, I've been making progress, but at a snails pace. I finally got two drives that will work alone with my 8080. They will both load and run CP/M. I also got them to kinda work together. I set the Shugart as A and the Siemens as B and the Shugart will load and run CP/M and do all the functions. Yet when I do a DIR B: I get a bad sector error. Then a ctrl c will re boot and A will run CP/M again. So, I switched the drives so that the Shugart was B and the Siemens is A. Same problem, the Siemens will load and run CP/M do all the functions, but if a DIR B: is requested I get a bad sector on B: error. I have the CPM disk in A and a formatted blank disk in B. So I think I'm back to having a bug in my CBIOS. When the command DIR B: is requested, first the A: drive has to find the DIR software on drive A then access directory on drive B I can see from the activity lights that A is accessed first and then B, then immediately after the error comes up. There must be a problem with the drive number being issued, yet the B drive is selected. Could the B drive get the bad sector error from being on the wrong track? Here I'm getting a little fuzzy, For the command A>DIR B:, the current drive is A and stays that way. Yet the DIR command has to call the CBIOS to read the B drive directory, which is a different drive, track and sector number. If I would put a short routine in my READ routine of the CBIOS I should see Drive=0, Track=something and Sector=something for the DIR command then after that read or reads (if more than one sector). Then for the B directory Drive=1, Track=something else and Sector=something else. Is this correct? It just came to me that the DIR command is a resident command, does the A drive need to be accessed at all? It's coming but slow. Mike