Kearney & Trecker Core memory, may be PDP8

Pete Turnbull pete at
Wed Nov 12 05:16:49 CST 2014

FWIW I'm pretty sure these boards are for a PDP-8/A chassis.  See below...

On 12/11/2014 07:13, Paul Anderson wrote:
> On Wed, Nov 12, 2014 at 1:09 AM, jwsmobile <jws at> wrote:
>> On 11/11/2014 9:12 PM, Jon Elson wrote:
>>> On 11/11/2014 09:18 PM, Johnny Billquist wrote:
>>>> On 2014-11-12 04:00, Jon Elson wrote:
>>>>> On 11/11/2014 07:33 PM, jwsmobile wrote:
>>>>>> I can't tell for sure, but this auction may be for  PDP8
>>>>>> core board.

>>>> The fact that the board have four edge connectors and not six
>>>> totally excludes PDP-11.

Not necessarily, but it's extremely hard to imagine how it could 
possibly be a Unibus board with four edge connectors on ABCD rather than 
CDEF, and the only QBus chassis those boards would fit would be an H909 
with a DDV11 backplane.  So, I'd agree it's highly unlikely to be any 
sort of -11.

I believe this system was based on a PDP-8/A because:

- the memory doesn't look /quite/ like my 11/34 core but does
   look like 12-bit PDP-8/A memory;

- the seller has several other cards from what seem to be the
   same system, or at least the same type, some of which have I/O
   connectors just above where the EF fingers would be - as found
   on some PDP-8/A boards, but not AFAIK on any others;

- the pattern of power/ground connections visible on the solder
   side of some exactly match the Omnibus layout but not Unibus
   or Qbus;

- a friend has a similar CNC system, built in a PDP-8/A
   chassis, with a papertape reader exactly the same as the one
   in one of the seller's other auctions.

There's a picture of it here, taken at DEC Legacy 2011:
It's a long time since I looked inside that system, so I can't be sure 
how many of its boards were custom items, or if they match the listings. 
  Unfortunately I can't go and look for a week or two :-(

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