Front panel switches - what did they do?

Eric Smith spacewar at
Tue May 24 19:30:10 CDT 2016

On Tue, May 24, 2016 at 3:09 PM, Brent Hilpert <hilpert at> wrote:
> Yes, I examined this in some detail last year after mention on the list, and wrote it up:

That's a great write-up! Thanks!

I'm not sure about how IBM TROS was driven, but the core-rope memory
I've examined was not from an AGC and didn't use the switching core
technique, so I wouldn't consider that decode technique to be an
inherent property of core rope memory, although it's certainly clever.

The core rope memory I examined had 64 words. Of the six address
lines, three fed a three-to-eight decoder with high-side drivers, and
the other three fed a three-to-eight decoder with low-side drivers.
Each of the 64 word drive lines was wired between a unqiue pair of
high-side and low-side drivers. That required significantly less
circuitry than a single-ended six-to-64 decoder.

The same technique was used for the X drive and Y drive of "normal"
core memory, such as the PDP-1 drivers for the Fabritek 4K planes in
the PDP-1 at CHM. (There was an earlier model of PDP-1 core memory
that might have used a different drive scheme.)  The X drive used one
pair of eight each high and low side drivers, and the Y drive used
another such pair.

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