DEC H207 Core Memory Boards

B M iamvirtual at
Fri Jul 10 17:49:41 CDT 2009

The PDP-11/20 that I have from 1970 has H207 core planes in the main
cabinet.  The H207 is part of the MM11E  subsystem.

Here are the boards in my PDP-11/20 cabinets:

The core plane should be documented in the "MM11-E Core Memory Manual"
 (see document DEC-11-HR3A-D).  I have a copy of the manual if needed.


On 7/10/09, Ethan Dicks <ethan.dicks at> wrote:
>  On 7/10/09, Rick Bensene <rickb at> wrote:
>> Hello, all,
>>  I recently came into possession of four DEC H207 Core Memory boards.
>>  They consist of a quad-width board that has a large number of signal
>>  steering diodes, with an attached daughter board that has a 4K x 16
>>  "Planar Memory" array made by Electronic Memories.  The boards all have
>>  original DEC warranty seals on them, dated June of 1971.
>>  I'm curious as to what DEC machine may have used these boards, and what
>>  support Flip Chip modules (X & Y drive, Sense/Inhibit, and addressing
>>  logic) may have been used with the core stacks to provide a 4Kx16 memory
>>  subsystem.
> They sound like the right size and date for an 11/20.  I have a few
> (since I have the rescued bits of a cut-up 11/20) and can check what
> you have against what I have.  Can you send me a picture off-list?
> I'll compare it with what I have, and I can confirm handle numbers for
> the sense/inhibit and XY boards (they should be on a master module
> list anyway - they were common in 1971).
> Unfortunately for me, I wasn't the only one from that company who got
> some parts.  I think I didn't manage to retrieve 100% of the core that
> was in the three-cabinet 11/20.  I am missing at least one core stack
> that I know of.  I was planning on a modern memory replacement if I
> ever get this machine put back together (it was stripped and the PSUs
> recycled before it hit the dumpster, and I saved the carcass and as
> many boards as I could).  My ultimate goal for this is to run first
> RT-11 to check it out, then the early version of UNIX that was
> recently demonstrated on simh (I still need to come up with an RF-11
> emulator; I think I have most of the rest of the hardware that's
> required).
>>  Give the 16-bit array size, I assume that it may have been used in a
>>  PDP-11, but I suppose (with four wasted bits) it could have been used in
>>  some form of PDP-8 system.
> Probably not.  There are 4Kx12 planes for the PDP-8 (I don't know the
> number off the top of my head) and it's not the same as what was used
> in the PDP-11.  Cores cost too much to "waste" 25% of them.
> -ethan

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