DEC PDP 11/23 - OK to use 22-bit memory boards in an 18-bit qbus?

Pete Turnbull pete at
Tue Jul 20 14:10:11 CDT 2010

On 20/07/2010 19:20, Scott M wrote:

> My concern is that the 18-bit PDP 11/23 does not have enough memory. 
> It currently has 128KB installed, with a maximum of 256K possible after a 
> memory board upgrade (M8067, MSV11-PK = 256KB).  How far do you estimate I 
> can get with just 128KB memory?  Can I get through Lions' book? 
> I am looking at adding wires to the backplane to make it a 22-bit machine, 
> and using a quad height qbus memory board, M7551 (available in 1MB, 2MB and 
> 4MB sizes).

I forgot to mention one other web page:
lists most of the memory options in a table.

Specifically, I can tell you that an M8067 MSV11-PK, and an M7551 
MSV11-Q are both OK in Q22-Q22 serpentine backplanes.  For the MSV11-P 
you need to ensure W1 and W2 are both in place to provide bus grant 

Pete						Peter Turnbull
						Network Manager
						University of York

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