Help identifying mystery Dataram VAX-11/750 (?) board

[Ethan Dicks]

On Thu, Jul 16, 2020 at 4:42 PM Josh Dersch via cctalk
<cctalk at classiccmp.org> wrote:
> On Thu, Jul 16, 2020 at 1:34 PM Josh Dersch <derschjo at gmail.com> wrote:
> > Picked up a board advertised as a "4mb memory board" for a VAX-11/750...
>
> I think I may have answered my own question here; looks like it's for a VAX
> 8000 series:

That makes more sense than a board that replaces the memory controller.

IIRC, the 11/750 has an architectural limit of 14MB of RAM, but that
might just be because of 8 memory slots (individual select lines), the
implementation of the L0016 memory controller, and that's what you can
hit with 2X 4MB boards + 6X 1MB boards.  I _think_ if you could have
gone to 16MB of RAM, DEC might have made a memory controller that
could control 3X 4MB boards + 4x 1MB boards or 4X 4MB boards, but they
did not.

I installed the extra memory line wire on the backplane of our 2MB
11/750 (and installed the L0011), but we never made that final jump
from L0011 -> L0016.  By the time that was available, we weren't going
to spend that kind of money on that machine.  It still has 8MB to this
day.

-ethan