DEC MKA11 and/or M8261/M8163

Johnny Billquist bqt at
Mon Feb 16 10:12:56 CST 2015

On 2015-02-16 09:42, Eric Smith wrote:
> On Mon, Feb 16, 2015 at 1:23 AM, Paul Birkel <pbirkel at> wrote:
>> Ah.  I need to count better.  There are *two* MKA11 per CPU, thus each only
>> *needs* just a 1 Mw configuration due to address-space limitations.
> I don't think so. The system shown in the photos has four CPUs, and
> four MKA11 boxes.  The MKA11 boxes are located in the right half of
> the cabinet housing CPU C, and the left half of the cabinet housing
> CPU D.  There's no evidence in the photos of there being any more
> MKA11 boxes other than those.  For instance, the right half of the
> cabinet housing CPU B clearly contains no MKA11 boxes, but rather what
> appear to be Unibus expansion boxes.  Only one photo shows the the
> right half of the cabinet housing CPU A open, and the view is
> partially obstructed by the CPU being extended out on its rails, but
> it definitely does not appear to have any MKA11 boxes either.


> If each MKA11 box has eight MS11-KE storage array modules (M7984),
> that is 256KW per MKA11, for 1MW total. While that's only just over
> half of the physical memory address space of the CPUs (1920KW, because
> the top 128KW is reserved for the Unibus address space), that seems
> like a very plausible real-world system configuration.

Box 0 and 2 are clearly setup to be interleaved with each other, and 
both have a 0 starting address, is is located in the cabinet holding CPC.
I wish I could read out what the thumbwheel switches on box 1 and 3 are 
set to in the cabinet holding CPD, as that would tell us how much memory 
are in each box.
But I would have expected the boxes to hold close 512KW per box. With 
the 128KW modules, that would be easy to reach.


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