CPU, not the KB11-B CPU of the earlier PDP-11/70's (prior to 1976 - the difference between the two was whether they took the optional FP11-B or FP11-C FPP). Not that it makes a big difference in your case; the 4 cache cards are the same in both. There used to be a seller on eBait (on the mid-East Coast - Baltimore, IIRC) who was selling -11/70 CPU cards (I bought a whole spare set from him) but alas he seems to have gone away (or sold them all; a quick search, both on eBait, and in my email, didn't turm him up; I can institute a deeper search if need be). cards; dunno if Guy Steele still has those clones he was selling. There are definitely some versions of Unix which will run fine on -11/70's without the FP11 (e.g. V6). The system binary is different for the with/without versions, though: in the assembler code which saves the state of one process before switching to another, there is code like: stfps (r1)+ which will probably get an illegal instruction trap in kernel mode on a machine with no FP11, and is therefore conditionally assembled (depending on if the particular machine the system is being built for has an FP11). Perhaps the later BSD versions look for the FP11 on startup, and adjust their behaviour appropriately, but I'm not familiar with them. V6 as distributed contains system binary for an -11/40, which will run on _any_ -11 UNIX will run on, and can be used to build appropriate system binary. (Diversion: I've never found out whether the KB11-B and KB11-C of the -11/70 used/could use the same backplane or not. By examining the prints for the boards of the FP11-B and FP11-C, and seeing on which pins they exchanged signals, and what signals they exchanged with the rest of the CPU, and on which pins, it should be possible to work it out. Ditto for the M8133 ROM and ROM Control of the KB11-B, replaced with the M8123 in the KB11-C.) (Interesting factoid: the M8123 is the only card shared between any variant of the -11/45 and -11/70: both the KB11-C and KB11-D use it. Of course, I think we're still missing a wirelist for the -11/70 backplane, of any variant; and the ECO history. There appears to have been at least one poorly documented upgrade; see here: http://gunkies.org/wiki/MK11_memory_system#CSR_Access for more.) Noel