5 Sep
2016
5 Sep
'16
8:03 p.m.
On 09/05/2016 09:28 PM, Brent Hilpert wrote:
I'd tend to be more pessimistic about this working.
In the 3-wire example there you can see how the S/I wire was split in half with a special
resistor network at one end to allow inhibit current flow
while at the same time configuring it as a balanced loop for the sense function.
My article certainly isn't the last word on the variety of implementations, I believe
there were 4-wire designs with sense wires parallel to
select wires as in the 3-wire designs for example, so you never know until you examine
the specifics at hand,
but I think it unlikely you'd have much success getting the inhibit wire to function
for sense, not without going to as much trouble
messing with the stack as if you tried to fix the sense wire.
Well, older core
memories had larger cores, which slowed
everything down as well as gave much bigger pulses when a
core flipped. That might make this exercise a bit easier.
If the sense wire is open I'd guess there's a
good chance it's at one of the end points where it's soldered to a terminal or at
an existing splice
from manufacture time and might be repairable if access could be had.
But, he has
to split the whole stack to at least access the
bad plane from one side. Already a pretty daunting
exercise. Still, fixing the bad wire, if the break is at an
exposed point, would be preferable than re-engineeering the
whole sense-inhibit circuitry. If the wire can be fixed,
there would be no engineering required.
I saw our old IBM 7094 memory, which had a combination of
tube and transistor circuitry, and one inhibit (or maybe
sense) wire had been burned up by a failed circuit. The
cores kept the wire cool, so the only places it opened was
where the wire looped around the plane. There were dozens of
bits of wire soldered to fix the places where it opened.
Sheesh, I sure wouldn't have wanted to be the CE who had to
do that repair!
Jon