> Guess I should document all this in the Computer History Wiki OK, done:
http://gunkies.org/wiki/PDP-11/24 > those prints (KT-24, and -11/24 backplane) would still be useful. Big thanks for Al for putting the KT24 prints up - very good to have them. > I guess it will require getting ahold of a backplane, and seeing what I > can find out with an ohm-meter. It looks like I'll still have to do this at some point, to confirm my theories about how the two busses are wired on the backplane (separation of UB and EUB address lines, and cross-connection of the data lines, for the EUB/SPC slots), since we still don't have any backplane info. Another mystery: The "PDP-11 UNIBUS Processor Handbook" (1985) says (pg. 4-10) that in the 5.25" box, "only one MS11-P memory module can be configured". Anyone know the cause/source of that restriction? I don't think it can be the backplane; i) AFAIK, the 5.25" and 10.5" (for which no limitation is stated) boxes use the same backplane, and ii) the 5.25" box can take more of the smaller MS11-L cards (albeit, again, limited - to three). So I don't think it can be 'the backplane doesn't carry all 22 address lines to all EUB slots' (although I will check); and the CPU does drive all 22. My next thought was that it's some power supply current issue, but on checking, that board only uses +5V, and there's nothing about limiting the number of ordinary boards when an MS11-P is in use. (I have to check the power supply specs, and compare with the board power consumption specs, to make completely positive there's no issue there.) So I can't come up with any technical rationale for that limit? Am I missing something? Or is it just DEC marketing, trying to limit how powerful the machine can be? Noel
