10 Mar
2015
10 Mar
'15
3:39 p.m.
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?
Somewhat...
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.
-ethan