First clue: for just about anything Q-bus, you can find the answer in the Micronotes. They're online at http://metalab.unc.edu/pub/academic/computer-science/history/pdp-11/ just click on "Micronotes". What you're looking for is specifically in Micronte #5, _Q22 Compatible Options_. It tells you Micro/PDP-11 H9278 4 X 3 Q22/CD and 4 X 5 Q22/Q22 Backplane In other words, just the standard BA23 backplane, the first 3 slots are AB/CD slots, the remaining 5 are AB/AB in a serpentine pattern. -- Tim Shoppa Email: shoppa(a)trailing-edge.com Trailing Edge Technology WWW: http://www.trailing-edge.com/ 7328 Bradley Blvd Voice: 301-767-5917 Bethesda, MD, USA 20817 Fax: 301-767-5927