PDP-11 memory question

From: Pete Turnbull <pete_at_dunnington.u-net.com>
Date: Sun Jan 6 15:33:29 2002

On Jan 6, 11:26, Jerome Fine wrote:

> (a) My experience with upgrading the backplane is VERY satisfactory. It
> was done by someone with sufficient skills with a soldering iron. And
> wire-wrap wire was used. The specific model was the VT103 which was
> a 4 * quad backplane, i.e. 4 quad boards or 8 dual boards. And
> resistors did not seem to be needed - perhaps because of so few boards.

Many of the QBus processors have a set of terminators on the CPU card, and
the QBus spec allows for the use of short bus length with light loads and
no extra terminators. The definitions of "short" and "light" are subject
to variation at short notice :-)

> (b) With regard to the use of the M8044 and M8045 memory boards, at
> one time I did that mod as well - using only 4096 bytes for the IOPAGE
> addresses (from 170000 to 177776). However, if I remember correctly
> (perhaps Megan can help with this aspect), it ONLY worked with either
> the RT11SJ or RT11FB monitors - i.e. UNMAPPED. As soon as I
> use the 11/23 board WITH the MMU activated, the MMU hardware under
> RT11XM forced the full 8192 bytes of the IOPAGE to be used - there
> was no other option. In addition, with the 11/73, it was NOT possible to
> use a 4096 Byte IOPAGE AT ALL

This sounds familiar. And to be honest, if you are running anything other
than RT11SJ, you probably have a lot more than 28KW of memory anyway, so
the saving is minimal. My advice would be not to bother trying to squeeze
another 2KW out of the system.

Pete						Peter Turnbull
						Network Manager
						University of York
Received on Sun Jan 06 2002 - 15:33:29 GMT

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