In my previous post I mentioned the 13037 handling 7900A drives. It does not. 7900A drives use a 13210 controller. 7905/7906/7920 and I think 7925 use the 13037 controller. The 13037A and 13037B are different mainly in the number of drives it will support. The B model will support more (8 i think), the A only four as I recall... The 13037C will support HPIB drives like the 7906H as well as the 7906 "standard" variety. Sorry for the boo boo. Jay West