DEC MKA11 and/or M8261/M8163

Johnny Billquist bqt at
Mon Feb 16 10:23:40 CST 2015

On 2015-02-16 10:28, Paul Birkel wrote:
> Need more experience finding Waldo, too!  I see that only C/D have the
> MKA11 in their associated-rack, so that's 1 Mw/CPU in the configuration
> seen.

It don't make sense to talk about the memory as per CPU, since it is 
shared between all CPUs...

> What's going on in the A/B associated racks?  I see what appear to be three
> BA11-L chassis (lower-A; upper- & lower-B).  And then a non-standard
> forward-facing vertical-orientation quad-height(?) module-cage in mid-B
> (any ideas as to what that might be; the bit of backplane visible to the
> left looks more like something QBus-era)?  Finally there's the large blank
> cover in upper-A ...
> What role might the 11/44(?) have played (really fancy serial-console)?
> Looks rather aged in appearance; surprising.

The serial consoles are the four LA120 in front of the system. Each CPU 
has its own console.

What 11/44 are you looking at?

> Would those have been MASSBUS drives in that 4-wide rack-set (perhaps
> hidden behind the lower panels; not sure about the row immediately above
> that, but the two to the upper-right appear to be RL02)?

Oh, are you talking about the two double-width cabinets to the side?
Right cabinet definitely holds two RL02 (or possibly RL01) along with 
two Unibux expansion boxes, from the look of it.

The left one is more tricky. Looks like two Unibus boxes there as well.

Top right, I would guess, is a DT07, which is a Unibus switch.
Top left is perhaps what you referred to as an 11/44. Not sure what it 
is. I don't think it's an 11/44, or any other CPU. Possibly another 
Unibus box. Below is a TK50, though.

Not sure what is below the DT07 either. Might be more parts of the DT07, 
or something unrelated.

I don't think there is anything behind the panels, but either way, there 
are no massbus drives there. Those require more space, and access.


> On Mon, Feb 16, 2015 at 3:23 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.
>> On Mon, Feb 16, 2015 at 3:05 AM, Paul Birkel <pbirkel at> wrote:
>>> Notice the two unused connectors on the M8162 there in the middle slot
>>> (#15).
>>> As this looks like an operational configuration, I infer that those two
>>> connectors are used for ... nothing?  Test points (through series
>>> resistors)?
>>> I see (how can one miss!) the address and data ribbon-cables.  The
>>> remaining white ribbon-cables must be for the box controllers. So, that
>>> looks like a 1Mw configuration.  Maybe 1.5Mw if, as you suggest, you're
>>> careful?
>>> Agree about the missing documentation :-<.
>>> Thanks for the better pic-pointer; knew that I can seen those in the past
>>> but couldn't recall where (and Google didn't help).
>>> On Sun, Feb 15, 2015 at 8:56 PM, Eric Smith <spacewar at> wrote:
>>>> It appears that the module utilization of the MKA11 is significantly
>>>> different than the MK11, so it must have a much different backplane.
>>>> The photo of the MKA11 only shows eight storage array modules, in
>>>> slots 9-12 and 18-21, though slots 5-8 and 22-25 might also be
>>>> available for storage array modules. The memory bus cabling is
>>>> obviously quite cumbersome, and adding storage modules in slots 22-25
>>>> looks like it could exacerbate that problem.The MK11 supports 16
>>>> storage array modules in slots 2-9 and 18-25. The module assignments
>>>> for the non-storage modules also appear to be different.
>>>> It's a shame that the KB11-Cm and MKA11 field maintenance print sets
>>>> aren't anywhere to be found. While the available 11/74 documentation
>>>> offers a description of how the KB11-Cm differs from the KB11-C
>>>> (mostly interlocked ASRB and cache bypass), it's a shame that we can't
>>>> study the actual details of how those changes were implemented.

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