DEC MKA11 and/or M8261/M8163

Paul Birkel pbirkel at
Mon Feb 16 02:23:01 CST 2015

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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