DEC MKA11 and/or M8261/M8163

Johnny Billquist bqt at
Thu Feb 12 04:24:25 CST 2015

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.

And in there, you can find that:

M8162 is a "Multiport Multiplexor Module"


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.


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