Memory options for an HP 1000 (HP 21MX / 2112A)

J. David Bryan jdbryan at
Mon May 18 00:31:10 CDT 2015

On Sunday, May 17, 2015 at 21:42, Marc Verdiell wrote:

> But the recently posted IO manual says it can support way more - up to
> 1.28M. 

That's correct, although the machine must be equipped with the Dynamic 
Mapping System (DMS) in order to access more than 32KW.  For the 2112, DMS 
is product number 12976A.  It consists of a card (the HP 12731A Memory 
Expansion Module) that plugs into slot 112 in the front card cage) and 
another card that contains microcode that implements the DMS instructions; 
the latter mounts to the main CPU board at the bottom of the chassis.

> I'm not sure yet how the HP 1000 memory works. Can I put larger (>8k)
> capacity HP 1000 memory boards in there to expand memory beyond 64k? 

Yes.  You can install any combination of memory boards that are compatible 
with your controller, which is the "standard performance" controller.  For 
example, I have an M-Series (2108B) with three 12747A 64K cards and two 
12998A 8K cards for a total of 208KW.

> Do I need to replace the memory controller with one that matches the
> larger capacity cards then? 

No, that's not necessary.  However, you must jumper each memory card to 
specify non-overlapping address ranges.  The "Standard Performance Memory 
Systems Installation and Service Manual" (5955-4310 April 1979) details the 
requirements; it's available from Bitsavers in the "1000" subdirectory.

                                      -- Dave

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