VAX-11/750 memory in 11/70 ?
ethan.dicks at gmail.com
Tue Mar 10 17:39:09 CDT 2015
On Tue, Mar 10, 2015 at 5:40 PM, Pontus <pontus at update.uu.se> wrote:
> Hi all
> I was told that VAX-11/750 memory could also be used in an PDP-11/70 (or
> maybe some other model). Is this true?
> I have also read that there are three kinds of memory boards for the 11/750:
> M8728: 256k byte memory array;
> M8750: 1M byte memory array;
> M7199: 4M byte memory array.
Yes. That sounds right (without looking up specific handle numbers),
depending on which memory controller you have in your 11/750. In
mine, I can handle 256K and 1MB boards. You also have to add row
wires to the backplane (I did this to upgrade a 2MB 11/750 to 8MB). I
have never had the fortune to run an 11/750 with 4MB boards (max of
14MB mixed with 1MB boards due to max physical address space of 16MB,
shared with other resources).
> (As well as some third party boards.
Yes... CMI and others. I've run a couple of those. They might or
might not pass DEC diags but the OS doesn't care.
> Which one of these, if any, could be used in an 11/70?
I am aware of the 256K array board working in the 11/70.
Also, the 1MB board that works in the 11/750 also works in the 11/725
and 11/730. I _think_ the 256K board should work in the 11/725 and
11/730 but since you are limited to 5 memory boards in that backplane,
1.25MB isn't enough to boot a VMS that's compatible with that CPU. So
electrically it would work, but logically, you wouldn't be able to
boot it. I suppose one could try 2x1MB+3x256KB and that might be
enough to boot an ancient VMS, but in practice, every 11/730 I've used
was crying for 5MB of physical RAM.
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