UNIBUS PDP-11 memory expander card

Noel Chiappa jnc at mercury.lcs.mit.edu
Wed Jan 28 13:02:18 CST 2015

So, I'm in the process of trying to read those old MIT V6 Unix dump tapes
(with a really big hand from Chuck, who did all the ugly work of actually
reading the bits off the tapes, for which he has my undying gratitude!), and
although I'm still trying to figure out what the format is, I did manage to
retrieve, more or less, a copy of the assembler startup/support file (m47.s; a
hacked version of m45.s), and it reveals that we were using an Able ENABLE
card to take our 11/45 out to more than 256KB.

I found a copy of brochure which very briefly describes/shows it here:


and although the picture didn't ring any bells for me, that must be it.

It looks like it has a UNIBUS connector (which I take it is 'UNIBUS out'), and
also some kind of 'over-the-back' connector which I assume is the bus to the
memory, which sounds (from a brief mention I found somewhere else) like it was
standard Extended UNIBUS memory in a separate backplane. (Although I could be
wrong; maybe the ENABLE plugged into the EUB backplane, and the UNIBUS
connector is 'UNIBUS in' from the CPU?)

I was unable to locate any real documentation for it online (maybe my
Google-fu just isn't strong enough), but if someone has any, or can point me
at any, I'd be grateful.

Any if anyone actually has one, in the flesh, that would be Really Cool!


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