On 2017-Jun-07, at 7:12 AM, william degnan via cctalk wrote:
> Where there any computers that used a "rectangular sense" core RAM?
> Whirlwind core is diagonal. This page describes the differences/evolution
> of the sense line.
>
> More: http://ed-thelen.org/comp-hist/Byte/76jul.html
>
> Were rectangular core planes used in any commercial/government computer
> that saw production activity, presumably the period 1953-1959? Whirlwind
> is known for diagonal sense planes, but was there a brief period when the
> core was "rectangular sense"
>
> I know core was added to Whirlwind as an
> upgrade, it did not launch into production with core. (right?)
From what the author writes, the memory he is examining uses rectangular sense
in a 4-wire arrangement, so the Spectra-70 would be one computer to look to.
Whirlwind started with a holding-beam memory (form of CRT storage-tube).
The problems with that inspired Jay Forrestor (whirlwind director) to come up
with something better and resulted in the development of core memory.
That original form of core design was 4-wire with diagonal sense.
I don't know how early the rectangular sense topology was developed but with
tighter & more complex control requirements I'd guess it was not in the
vacuum-tube era.
'Rectangular sense' is inherent in 3-wire core memories (have to disagree with
Jon there.)
The sense wire being parallel to one axis of address wires makes it possible
for it to do double duty as the inhibit wire, and so eliminate the threading of
a fourth wire.
In my observation, the 3-wire format came in somewhere around the very late
60s/1970.
For example, according to the maintenance manuals, the pdp-8/i (1968) is 4-wire
diagonal sense, the pdp-8/e (1970) is 3-wire rectangular sense.
The HP2116 versions saw a similar development timeline for the memory.
I think I can say most to nearly all of the core memories of the 70s were
3-wire and hence rectangular sense,
although I've seen one example of a smaller memory from 1974 still using
diagonal sense.
Speculating in part, but It would make sense as the development history:
1. Original diagonal sense as the easier & more obvious way to minimise
capacitive & inductive coupling.
2. Somebody developed the rectangular sense, probably to help simplify
the threading.
3. Somebody noticed the now parallel address & sense wires would allow
combing the sense & inhibit wires, coming up with the 3-wire arrangement and
simplifying manufacturing considerably.
