DEC MKA11 and/or M8261/M8163

Paul Birkel pbirkel at
Sun Feb 15 04:43:07 CST 2015

On Sat, Feb 14, 2015 at 2:24 PM, Johnny Billquist <bqt at> wrote:

> On 2015-02-14 19:14, Paul Birkel wrote:
>> Thanks Eric.  That might explain how I came into possession of one M8162
>> module.  The 11/74 never entered my mind because encountering even a piece
>> of one of those is ... unlikely :->.  Using up unsold inventory makes
>> sense; I guess that an MKA11 wouldn't function without a full complement
>> of
>> modules, even if some serve no real purpose.
> The MKA11 is really not much different from an MK11, and you can use an
> MKA11 in a normal 11/70 system as well as far as I understand. Essentially,
> the MKA11 is just a multiported MK11 box. And the multiporting is achieved
> through this extra module, that fits (as far as I can remember) in the
> standard MK11 box.

As I understand the wording in the slim documentation, each port will
require another pair of M8158/M8159 Address/Data Buffers.  So a dual-ported
unit would need two of these pairs, and a quad-ported unit four pairs.  The
M8162 then coordinates the (up to 4) pairs.

> All the other modules in the MKA11 are the same as in the MK11.

Except the numbers of buffer pairs, there being up to 4 pairs possibly

The MK11 chassis was already full, so they would have had to reduce the
complement of MOS-modules in the MKA11.  By the time of the 11/74
presumably it was the case that increased-density ICs would have allowed
more-RAM-per-module, so the loss in MOS-module count per MKA11 would have
been acceptable.

>  I've looked more closely at the pair of top-edge connectors (the ones like
>> the 20ma SLU connectors).  Each have 6-of-8 pins wired *thru* a 1K 1%
>> resistor to a separate pin on tab F.  So there are twelve lines running to
>> tab F, with resistors in series, and nothing else on those paths.
>> The rest of the module is a mix of S and LS SSI chips, and a couple of
>> what
>> appear to be multi-tap delay lines, plus 5 diagnostic LEDs (unlabeled).
>> Would the KB11-CM have had special cabling to connect in this manner for
>> out-of-band signaling, and then why series resistors (rather than, e.g.,
>> pull-ups for an OC line driver)?
> I don't think so. There is not out-of-band signalling. But you do have a
> control panel for the memory box, on which you can control the box. I would
> suspect this would be for that.

Right (line-diagram Figure 1-1 is pretty crude).

> (I think there are some extra controls for an MKA11 compared to the
> standard panel of an MK11, which is for (I think) setting the memory
> on-/offline for individual CPUs, and possibly something more. It should be
> in the documentation I put in a link to.

Beyond the claim that "Port Controls" exist, and where they get installed
in the racks, I don't see any.

Best available images seem to be at:

I like the user-supplied color-coded dots :->.  Can *almost* decipher the
front panel labeling, too.

That said, they look to me to be identical to the standard MK11 "Box
Controller".  No clue there what the extra cabling might be doing.  Maybe
the extra cabling doesn't actually involve the "Box Controller" on the
front panel at all.  Perhaps simply cross-linkage among the Port
Multiplexers in different MKA11 (can't think of a good reason for that,

>  On Wed, Feb 11, 2015 at 2:55 PM, Eric Smith <spacewar at> wrote:
>>  On Sat, Feb 7, 2015 at 7:25 AM, Paul Birkel <pbirkel at> wrote:
>>>> I don't understand the role of the M8162 "Port MUX A module" and M8163
>>>> "Port MUX B module" that the field-guide claims to be part of the MK11.
>>>> They aren't part of the MK11 as far as any documentation that I've read
>>>> regarding it. [...]
>>>> Do these modules really belong to the MKA11, rather than the MK11?
>>> The MKA11 was the multiported version of the MK11, intended for
>>> multiprocessor (11/72 and 11/74) systems. it makes sense that it would
>>> have some "port mux" modules, though I've never seen any documentation
>>> on it.
>>> Reportedly some 11/70 systems were sold to AT&T with the KB11-CM CPU
>>> and MKA11, apparently just as a way to use up the hardware that was
>>> built for the cancelled 11/74.
> --
> Johnny Billquist                  || "I'm on a bus
>                                   ||  on a psychedelic trip
> email: bqt at             ||  Reading murder books
> pdp is alive!                     ||  tryin' to stay hip" - B. Idol

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