Just slot numbers by themselves aren't much use, because if there are any non-UNIBUS backplanes (e.g. custom backplanes for core memory, for an RH11 - which has its own custom backplane, you can't use a regular SPC/MUD 'UNIBUS' backplane to hold it), we need to know what those are, and where. Note that many boards can only go in a specific slot in a custom backplane, and vice verse - some slots in such backplanes will only hold a specific kind of card. Taking the RH11-AB as an example: it comes with a 9-slot custom backplane. Hex RH11 boards M7294 and M7295 go in slots 3 and 2, respectively (and nowhere else, and nothing else can go in those slots). UNIBUS A in is in slot 1, connectors A/B; UNIBUS A out is in slot 9, connectors A/B. UNIBUS B in is in slot 8, connectors A/B; UNIBUS A out is in slot 7, connectors A/B. The RH11 backplane has some slots which are not needed/used by the RH11; those are wired as SPC slots; slots 7, 8 and 9, connectors C-F (the A-B connectors in these slots are UNIBUS, per above), are SPC slots. That means that they need _at least_ a G727 single-width card (the little square grant continuity cards which jumper BG4-7) in them if there is no other device plugged in. If the NPG wire-wrap jumper on the backplane for that slot has been removed, you'd have to use a G7273 dual-width jumper card, to jumper NPG also. So, looking at your list; first, a comment about naming: 9/11: M9202 (1-2) 11: M7297 (3-4) 11: 7296 (5-6) This looks like slot 1 of an RH11 backplane. Standard practise it to use letters for the vertical, and numbers for the horizontal, for positive identification. So standard nomenclature would be to say that the M9202 is in connectors A/B, the M7297 in C/D, and the M7296 in E/F. (Individual pins are named xYZn, where 'x' is the slot, 1-N [where N is typically 4 or 9]; 'Y' is the connector, A-F; 'Y' is the pin, A-V using the 'DEC alphabet'; and 'n' is the side, 1-2. The NPG jumper is CA1-CB1 in all SPC/MUD slots, i.e. 1CA1-1CB1 in slot 1.) The stuff starting in slot '21' looks like a DB11 UNIBUS repeater, but I have no idea how large a backplane that is, and what the various slots/connectors in it are used for. It's almost certainly custom wired. It looks like slot 31 starts another backplane. Given the cards that are plugged in (LP11, DL11, etc), it's probably a 'UNIBUS' backplane (i.e. SPC or MUD slots). Noel