Yeah, mine (a late /55, actually) has the _exact_ same wires at Josh's. So that's probably the final ECO level. Image here: http://ana-3.lcs.mit.edu/~jnc/tech/pdp11/jpg/1145CPUBackPlane.jpg if you're interested. (Not a great image, but OK; I can try for a better one if there's a need.) The -11/45, /50 and /55 are all the same CPU (KB11-A or -D), so the same backplane/everything, but differ only if they were sold pre-configured with the MS11 Fastbus memory. And of course some /45's (especially those sold before the introduction of the /50 and /55 as sales options - I have a /45 price list from Sep, 1972 which lists the /45 and /50 but not the /55; and one from Jan, '73 which only lists the /45 :-) were upgraded (possibly after sale, after the /50 and /55 appeared) with MS11 - or possibly some /50's and /55's had the MS11 removed at some point. So the number doesn't mean anything; one has to look at the boards. Noel