Jerome Fine replies: The last time (I only EVER did it once) I put the dual board RLV11 board set into an ABAB (Q22) backplane, I destroyed the boards. As Tim Shoppa states, they MUST go into two slots which are both ABCD. In a BA23 box, the top 3 slots are ABCD. I presume that if you put the CPU in the top slot and the RLV11 in the 2nd and third slot, it might work. Has anyone ever done that successfully? Also, if you are running RT-11, you can still use more than 256 KBytes in the system, just don't try to do it with the RLV11. PIP can copy anything from the RL02s to the RD53 and then let you use the rest of the memory over 256 KBytes. What backplane are you using? Most BA-11 backplanes are ABCD with 9 slots including a terminator board which MUST be the last slot you use and is usually the last physical slot since bus grants are not a problem with regard to termination. The ABCD slots are quad width and accept dual boards as well, but the other half MUST stay empty. The RX02 requires a dual M8029 (I think it is called an RXV12) with a 40 pin cable. The RQDX2 allows RD51, RD52, RD53. It is a quad board (a -YB). Most will not accept an RD52 from an RQDX1 without re-format. If your backplane is stuffed, what else do you have? Sincerely yours, Jerome Fine