You wrote... Off the top of my head without checking the manuals for accuracy..... The 13037 was HP's bid to get away from having a different controller in the backplane for each different drive. Previous disc interfaces were particular to fixed head, moving head, drum, etc. In addition, the interfaces in the card cage always took more than one slot as I recall. There is a 13037A, B, and C that I know about, I have nothing that refers to the D model. With the 13037, one interface card goes in the card cage. Cables go from this to a rack mount box (about 5 inches tall, about 28 inches deep). Inside this rackmount box was a separate microprocessor board and additional disc interfaces. The drives in turn were connected to the rackmount box. The particular features of the 13037 stuff was that more than one system could be connected to the rackmount microprocessor, but mainly different types of discs could be connected. The 13037B could do 7905, 7906, and 7920 drives. The 13037C added the capability to do both MAC and HP-IB drives. I have it on good word that the A and B models were junk (comparatively), and that the C model was the "one to get". I might have a spare manual on the 13037, I'll have to check. I do have a 13037C under refurb at the moment. Regards, jay West