Double Buffer RK11-C

Noel Chiappa jnc at
Sun Dec 4 20:16:49 CST 2016

    > From: Fritz Mueller

    > But then over at bisavers, I see this:

Yes, that's the panel I found the picture of in the RSTS-11 brochure a while

The picture in the brochure is not very very hi-res, but Al Kossow recently
located some original photos in the DEC section of the archive, and the image
you sent the URL for is one of them.

I've been puzzling over what this thing is.

It looks 'kinda-sorta' like an RK11-C panel (the registers it shows are sort
of the RK11 registers), but if you look at the print for the "RK11-C
Indicator Connectors: RK11-C-23" (page 34 of the RK11-C Engineering Drawings
PDF), you can see the pinout, and it doesn't match.

E.g. look at the lower right line of lights on the panel: 4 bits of Bit
Counter, a blank, 8 bits of Internal Word Counter, a blank, and three bits of
Major State; now look at the RK11-C prints, connector B32: 4 bits of Bit
Counter, 8 bits of Internal Word Counter, a blank, Postamble, Checksum, Data,
Header, Preamble.

Close, but different.

One thing I have been wondering about is that "RK11-C" - that implies that
there was a -B, etc. I wonder if this panel goes with one of them? (Or perhaps
it is a custom prototype?)

I have never been able to find out anything about an earlier version of the
RK11: the earliest Peripherals Handbook that I have is the 1972 Red/White
one, and it only talks about the -C. Also, the Spare Module Handbook (a
fantastic resource, it lists the boards in almost every PDP-8/10/11 option)
mentions the -C and -D, but no other ones.

However, given the example of the KT11-B, which was totally unknown until the
documentation for one showed up with the -11/20 in Arizona, thereby proving
that there _was_ a KT11-B before the KT11-C (the -11/45's MMU), I would guess
that there likely _was_ an RK11-B, and perhaps this panel goes with that (or
an earlier one).

Any further information would be most welcome.


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