25 May
2016
25 May
'16
12:23 p.m.
On 2016-May-24, at 5:30 PM, Eric Smith wrote:
On Tue, May 24, 2016 at 3:09 PM, Brent Hilpert
<hilpert at cs.ubc.ca> wrote:
Thanks, I had been perplexed by the descriptions of the AGC ROM available in the usual
places (the AGC books), they gloss over aspects or in some cases are inaccurate, and once
looking into the AGC ROM in detail realised they were (at least) two techniques being used
in woven-wire/transformer ROMs.
Yes, I examined this in some detail last year
after mention on the list, and wrote it up:
http://www.cs.ubc.ca/~hilpert/e/corerope/index.html
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.
I think this just goes to the etymology of the phrase "core rope" - whether one
chooses to apply the term only to the switching-core technique (where I believe it
originated), or generally to woven-wire ROMS which take on the appearance of a rope (which
seems to be the common use these days).
It appears the switching-core ROM technique was a practical application or outcome of the
more-general "magnetic core logic" technology of the 50's.
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.