DEC MKA11 and/or M8261/M8163

Paul Birkel pbirkel at
Mon Feb 16 03:28:32 CST 2015

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

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.

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)?

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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