Ongoing core memory discussion (was Re: How scarce (valuable) is core for the PDP-8?)

From: allisonp_at_world.std.com <(allisonp_at_world.std.com)>
Date: Tue Apr 20 15:52:40 1999

> Funny you should mention demo core. I have had in the back of my mind for
> several years now a project: demonstrate memory storage by building a mini-
> core mat on top of an FPGA socket and drive it via some kind of parallel-
> port A-D/D-A interface. The purpose of the demo would be to stick the
> core mat into a ZIF socket, program it, display the bits on the screen,
> remove the mat from the socket, turn it around and show how the bits have
> moved... not particularly practical, but a good visual demonstration of
> the technology. A special bonus is that the demonstrator can prove that
> core is non-volatile by letting the audience see the plane out of the socket

Why a/d and d/a?

> I'm thinking of a 4x4 or a 5x5 mat; nothing larger than 8x8. The test jig

actually 8x8 by one bit is fairly easy to do.

> of the sense amps and inhibit drivers for several PDP-8 models. Is it
> possible to simplify that circuit if you knew that you had read cycle time
> of several or tens of milliseconds? Perhaps by having one circuit to control
> all the X lines, one circuit to control all the Y lines and some sort of
> analog multiplexer?

Foo, wrong way to go. Too top heavy. Also the cores even if slow switch
in the microsecond range.

> How do the different dimensions affect this all? (Most ferrite beads I've
> seen are taller than their diameter (HoHo's, not KingDons, if you will).
> In other words, the ferrite beads have a different aspect ratio compared
> to the #2 nuts (or a standard ferrite core). How does this affect usability
> as a memory device?
Received on Tue Apr 20 1999 - 15:52:40 BST