What is the KH11-A? (was Re: Differences between the PDP-11/15 and PDP-11/20)

Noel Chiappa jnc at mercury.lcs.mit.edu
Mon Aug 22 07:16:43 CDT 2016

    > From: Ethan Dicks

    > Second, many/most of the CPU modules are -YA variants, and the "PDP-11
    > Field Guide" mentions that they would be part of a KH11-A. About the
    > only description I can find for what that is, is a single mention ..
    > of the "large-system capability option" related to the DT03-F Unibus
    > switch requirements. Anyone know what this is?

I've been told that it's a revision to the CPU timings to reduce NPR latency,
although I have no details; I had previously looked online, and was not able
to locate anything about it.

    > a full set of boards for a KE11-A. I have been sniffing around for a
    > KE11-B (single-board version), and now, I don't need to (as long as
    > this one works or can be repaired).

Doesn't it need a custom backplane too? Do you have that?

    > my goal all along has been to fire up enough hardware for Warren
    > Toomey's reconstruction of ~1972 UNIX

Maybe someone here can scratch a mental itch for me; I recall reading
_somewhere_ about some early PDP-11 memory management thing used on early
PDP-11 Unix that supported the KE11 (which is a memory-mapped device) by
having a small window that allowed user code access to the KE11. IIRC, it was
a DEC thing, not something home-rolled at Bell. Does this ring any bells for


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