[rescue] DEC PDP-11/23 memory expansion

Patrick Finnegan pat at computer-refuge.org
Sun Jul 11 12:55:25 CDT 2010

On Sunday, July 11, 2010, Scott M wrote:
> I recently acquired a DEC PDP-11/23 in a VT103 chassis.
> (Terminal + computer in a single package).
> Nice computer, but a bit short on memory to run 2.11BSD Unix.
> This page:
> http://en.wikipedia.org/wiki/PDP-11
> says:
> > PDP-11/23 - 2nd generation of LSI (F-11), early units only
> > supported 248 KB memory, but could be modified for 4 MB support.
> I cannot find details on this "modification" anywhere.
> Does it involve removing the CPU board (M8186 KDF11-A), and replacing
> it with another, or can the original be somehow modified for 22-bit
> operation? Also what 4 MB memory board is recommended?
> Thanks for your help.

I believe that you'll need to wire up bits 19-22 on the address bus, on 
the qbus backplane in the terminal.  Google will help you figure out 
what pins those are.

After you have that, any qbus-only memory board (ie, not PMI memory from 
an 11/83 or a QBUS VAX) should work.  Something like an MSV11 or 3rd 
party equivalent.  

Purdue University Research Computing ---  http://www.rcac.purdue.edu/
The Computer Refuge                  ---  http://computer-refuge.org

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