PDP11 NSC RAM questions

Jerome H. Fine jhfinedp3k at compsys.to
Mon Mar 26 22:02:08 CDT 2007

 >Curtis H. Wilbar Jr. wrote:

> I've purchased a memory board for PDP11.
> It appears to be a National Semiconductor Q-BUS memory card.
> It has 980110014-001 on it.  I find (currently) no markings saying
> like NS23D, NS23M, NS23S, NS23E, etc....
> It is populated with MMC3764N-15 chips.  There are 144 chips
> total.
> I'm still a newbie on 11s...  but, if my internet searches are correct
> those chips are 64k x 1 ram modules.  So it takes 8 of them to make
> 64 kilobytes.  Assuming there is parity, 144/9 make 16 sets of 9
> chips each with 64 kilobytes + 1 parity bit per byte (9th chip).
> This math makes it out to me a 1MB module.
> Can anyone confirm that is what it is ?  I bought it as a 4MB module.

Jerome Fine replies:

Assuming that your internet search and math are correct, you do have a 1 
memory board.  I don't have the time at the moment to check it out, but 
I tend
to believe you are correct since I have never run across a 4 MByte memory
board from National Semiconductor.

> Also, I believe this came out of an 11/73.  Will this work in an 11/83,
> and if so, does it operate as PMI memory ?
> Thanks in advance from all you PDP11 gurus out there.

YES!!  It will work in a PDP-11/83, BUT as only ordinary memory,
NOT as PMI memory.  With your memory board, the CPU is in the
first slot and the memory is usually in the next slot(s), but the latter is
NOT a requirement.

You are correct that a PDP-11/83 will allow PMI memory.  However,
ALL  KDJ11-Bx boards are able to use PMI memory since the CPU
module is what activates PMI memory provided the PMI memory
board is placed in the FIRST memory slot(s) and FOLLOWED by
the KDJ11-Bx module.  IN  ADDITION,  ALL of the slots which
hold the memory and CPU  MUST be ABCD slots.

In a BA23, the first 3 slots are ABCD followed by 5 ABAB slots.

In a BA123, the first 4 slots are ABCD followed by 8 ABAB slots.

In BOTH the BA23 and the BA123, the ABAB slots are serpentine
with regard to the bus grant.  Ask if you have a question!

> And... if this isn't PMI memory, and if is only a 1MB board, would
> anyone want to take in in trade towards a M8637-EF (MSV11-JE)
> to go along with the existing MSV11-JE I have.

I will keep you in mind if I ever dispose of my PMI memory.

Any other questions?

Sincerely yours,

Jerome Fine
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