DEC MKA11 and/or M8261/M8163

Paul Birkel pbirkel at
Sat Feb 14 12:50:02 CST 2015

So ... I should have stretched my mind a bit more in the space of "stuff
like an 11/70 but which is not an 11/70 ...".  Encountering even a bit of
an 11/74 was simply not something that I ever considered.  Thanks for the
pointer Johnny!

Looking at the preliminary Docs, Figure 1-1, where a two-processor
configuration is laid out, with two MKA11, it appears that they have their
ports cross-wired and then driven from a panel-control of some sort.  So
there's 6-bits for MK0A/MK1A, and then a separate 6-bits for MK0B/MK1B (see
earlier response to Eric about the connector arrangements).  Not at all
clear to me how that wiring relates to the description in 1.4.2.  Need to
think about this some more ...

It seems then that the Field Guide has both of these modules mis-assigned,
and the second misnamed.

I wonder if the relationship between the M8163 and M8164 is an either/or
and they go into the same slot given that Table 1-1 mentions only a single
Multiport Multiplexor (M8162) and the naming in Table 1-3 for the M8163 is
"Single Port Jumper Card"?  I guess that's what you're thinking as well.

What is the purpose of the "panel" Port Controllers, given that they seem
to be not connected to any control signals from the CPU? (Figure 1-1)

Does the "T" in the symbology in the Figure perhaps indicate "Terminator"?
If so, that seems to suggest that the signaling is out one control, into
the second and then off "through" a terminator to the panel Port Control?

Honestly, Figure 1-1 doesn't look to me like a shared-memory arrangement
... so I'm probably misinterpreting some of those lines at the moment.

Thanks for all of the additional clues and pointers guys!

On Thu, Feb 12, 2015 at 5:24 AM, Johnny Billquist <bqt at> wrote:

> On 2015-02-11 20:55, Eric Smith 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.
> I don't think that 11/72 is a valid designation. All documentation I've
> read only calls it an 11/74, no matter how many CPUs you have.
> You can find documentation on the MKA11 in the 11/74 documentation.
> (See
> EK-70MP-TM_PRE_1170mp_Prelim_Technical_Manual_1977.pdf)
> And in there, you can find that:
> M8162 is a "Multiport Multiplexor Module"
> and
> M8163 is a "Single Port Jumper Card".
> So yes, both of these cards are for the MKA11.
> I would guess that you use the M8163 if you have an MKA11 but just a
> single CPU.
>  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.
> I've heard similar. And also that CPU cards for the 11/74 were installed
> in 11/70 systems. The differences don't matter for normal operation, and it
> will work like a normal 11/70. You can detect if differences if you try,
> but the system will work like any other 11/70.
> Only a few CPU modules differ between an 11/70 and 11/74 anyway.
>         Johnny

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