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

Ethan Dicks ethan.dicks at gmail.com
Sun Aug 21 22:36:14 CDT 2016

On Sun, Aug 21, 2016 at 1:53 PM, Noel Chiappa <jnc at mercury.lcs.mit.edu> wrote:
>   http://gunkies.org/wiki/KA11_CPU

Interesting stuff on the KT11, but tangentally, I've been going over
my pile of parts (that I've described a few times over the years) from
an 11/20 I pulled from the dumpster at work 30 years ago.  I finally
got around to photographing the module handles and inventorying many
of the boards and I've learned a thing or two and have generated a
question or two.

First, the manufacture date for most of the parts is in 1972.  The
front panel says "11/20", so that all jibes.  I appear to have a CPU
(more below), an M7800 DL-11 console interface (not the older
multi-board KL-11), a lot of MM-11 4K core sets, and a happy surprise
(again, more below) and not much else from that extraction (no
bootstrap card, for example, or peripheral adapters).

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 (in
PDP-11_PeripheralsHbk_1973.pdf) of the "large-system capability
option" related to the DT03-F Unibus switch requirements.  Anyone know
what this is?  I'm reasonably certain it doesn't matter for my needs,
but I'm curious.

Third, the happy surprise is 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).
This excellent for me since my goal all along has been to fire up
enough hardware for Warren Toomey's reconstruction of ~1972 UNIX (v1
kernal plus v2 utilities).  Yes, I know I can run that on SIMH (I
have), even wrapped up in a Docker (I will), but I've wanted to run it
on the real hardware for 11 years and I'm one step closer.  I have a
RK11-D that works, and an RK11-C that will likely require much
attention (never tried to use it), so the only thing I'm really
missing (besides enough time to repair/debug all of this) is something
to emulate an RF11 for the swap disk.  I'm now doubly sad that I lost
my Diablo 30/RK03 in a flood 25 years ago, but I'll be functional with
an RK05 or two.

Fourth - I don't think I got the H720 power supplies with this (or the
fans) - that was what I think was removed prior to this unit hitting
the dumpster.  I may have the G772 power cards (and then again, I may
not), but those wouldn't be hard to reproduce.  I am entirely
satisfied with modernish switching supplies, but I see the H720 puts
out about 15A of +5V and -15V, plus -22V for the core and +8V for the
front panel bulbs.  The bulb voltage is probably no big deal to come
up with, but -22V is a bit of an oddball.  I'm also willing to forego
100% core in favor of MOS memory, including any modern repros that
come out in the next year or two.  To start, finding even one H720 to
run the CPU box (I have 2 more boxes for the rest of the memory) would
be enough to get going.

So... for now, as I continue to pull the parts together, my real
question is, what is a KH11-A?

Thanks for any enlightenment.


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