PDP-8 core memory problems.

Vincent Slyngstad v.slyngstad at frontier.com
Tue Sep 6 08:41:25 CDT 2016

From: "Mattis Lind: Tuesday, September 06, 2016 2:11 AM
> * Use a PDP-15 MM15 stack and sense/inhibit boards.
> I have several off these. Adding a small backplane, put the X/Y drivers,
> sense amp/inhibit drivers and level converters there and then adapt to the
> existing slots for the memory module. It would be a horrible mixture of TTL
> and transistors. But it would still be core memory.

There's a guy on eBay who periodically offers stacks for 8/I or 8/L:

Those might (or might not) be more straight-forward to interface (though 
DEC's proof of concept is a TTL interface).

> * Use solid state technology. Possibly inside the memory box so it looks
> real but emulates the actual core memory module.
> Any ideas how this could be done in the best way?

I did some (theoretical) work on a core replacement for the 8/S 
a few years ago based on some ideas from John Price.  That's 
embedded in the "memory" drawing in 
(See sheet 2; most of the schematic is just the schematic of an 8/S.)

Somewhere I also explored a notion of pulling the inhibit driver 
and sense amp stuff, replacing the stack itself with a memory board, 
then replacing the inhibit drivers and sense amps with interface 
boards that knew how to talk to the new memory board.  If I recall, 
that was in the 8/I or 8/L context, though.

I never built any of it, it was just a thought exercise.  There  seemed 
to be plenty of board real estate to work with, though.


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