And alas, we don't seem to have any prints for that card (although we do have what amounts to a tech manual, so maybe we can create a set, with a certain amount of tracing with an ohmmeter), so at the moment, at least, fixing them isn't so easy. Well, that's a very good sign... Definitely; the code on the Dilog card might not support that controller properly (even though it seems to recognize "DU"). If you have less than 256KB of memory (so Q22 processors won't wrap around, when trying to size memory, and think there's memory there above 256K - although Q18 memory probably will stop responding at 248KB, anyway), pretty much everything _should_ work, I would think. The high address lines being put out by the processor, DMA devices, etc should just have no effect. Although the details get tricky... E.g. if you don't have BDAL18-21 for a Q22 memory card, what will its bus interface do when faced with those lines, which aren't driven in any way - _especially_ not pulled up by terminators? Some DEC memory cards (e.g. MSV11-L, M8059) have jumpers to run in either Q18 or Q22 mode, to work around this. No, if you have less than 256KB of memory, the high bits should just be ignored (I think - I haven't actually tried this, to be absolutely sure). I have modified an H9273 backplane (Q18) to H9276 (Q22), and it works fine; all I did was bus all the BDAL18-21 pins together: pretty easy, as it's a Q/CD backplane, not a Q/Q - just run a wire down, and solder it to each pin as it goes (those backplanes don't have the pins stick out far enough for wire wrap). Q/Q will be only slightly more complicated (since you have to bus down one side, then run the signals up and across to the top of the other side, and then bus them in turn - do it this way, to avoid creating a branch in the bus which will encourage reflections); I have done this mod on a Q18/Q18 backplane (a Sigma Q18/Q18), but have yet to actually try it. The only complication might come with termination/pull-ups. Not all backplanes have these built in (e.g. the DEC H9273/H9276 don't). But you might not need them - IIRC both the 11/23 and 11/73 have on-board termination which will pull the lines up. But if you _do_ need them... best bet, unless you want to start soldering resistors to the backplane, is a terminator board with Q22 pullups. That's a whole separate discussion which I will leave for the moment... :-) Noel