11 Mar
2015
11 Mar
'15
11:43 a.m.
On Wed, 11 Mar 2015, Paul Koning wrote:
There's an article online from Byte Magazine, July 1976, about
coincident current core memory:
http://ed-thelen.org/comp-hist/Byte/76jul.html
Mike Loewen mloewen at cpumagic.scol.pa.us
Old Technology http://q7.neurotica.com/Oldtech/
On Mar 11, 2015, at 1:45 PM, Rick Bensene
<rickb at bensene.com> wrote:
OK, while we're on the topic of core memory sense circuitry, in some of
the old calculators that I've come across (a good example being the
Casio AL-1000 -- http://oldcalculatormuseum.com/al1kck10l.html) ) there
are transformers (pulse transformers) in the core memory sense
circuitry. What purpose would these serve, and why are they used in
some core memory applications, and not in others? In the case of the
AL-1000, similar transformers are used in the X-Y drivers as well.
Core memory sense amps and drivers are that mystical analog stuff that I
don't understand very well :-)
Can someone enlighten me about these transformers?
I found a very good detailed description of high speed core memory in the CDC 6600
training manual ? copy available on bitsavers at
http://bitsavers.trailing-edge.com/pdf/cdc/cyber/cyber_70/fieldEngr/6014740…
. Chapter 4 describes the memory. It includes schematics, and a pretty detailed
description of how the circuits work.
Those memories are a bit more complex than usual; there are two inhibit wires rather than
one, and the inhibit does not cover the whole core plane but only a part of it (i.e.,
there are several independent inhibit current paths). It doesn?t say why. My best guess
is that this is to keep the inductance of the inhibit wire similar to that of the X and Y
wires, so the same driver design works with roughly the same timing. This memory is much
faster than most other memories of the same era: 1 microsecond full cycle, in 1964.