From Newsgroup: comp.arch
On 10/10/2024 7:27 PM, Sarr Blumson wrote:
MitchAlsup1 <mitchalsup@aol.com> wrote:
On Wed, 9 Oct 2024 19:18:40 +0000, Kerr-Mudd, John wrote:
I remember the PDP-11/20 in the computer lab at NCR.
Last person out at night would flick the power switch OFF, and
the computer was OFF in 1/60 of a second.
First person in would flick the switch ON and the computer was
back where it was turned off in 1/60 of a second.
We used the 11/20 as a remote debug device for the 8085 cash
register machine(s) we were building.
Core memory: slow to access but also slow to forget.
Core memory was before my time, but I remember reading somewhere that it needed to be preheated to a certain operating temperature in order to
write to it (because the hysteresis energy of the ferrite rings was temperature dependent, and it needed too much power to flip the bits at
lower temperatures).
I am left to wonder if one could have made a non-volatile
electrochemical memory with "ye olde" tech;
Say, for each memory cell:
Two lead plates and a thin separator
With a water + sulfuric-acid electrolyte;
3 states:
A: Plate A is lead dioxide, Plate B is lead
Electrolyte is live.
B: Like A, but with the plates reversed;
C: Plates are lead sulfate, preferably avoided;
Too strong of sulfate, memory cell dies.
Or, two iron plates, and a separator:
Similar, but using a potassium hydroxide based electrolyte (1).
*1: In the C state, the plates would try to convert to iron-potassium
ferrate, but this process would cause the electrolyte to become slightly acidic (depleting oxygen and leaving an excess of H+ ions), which would decompose the ferrate. In the A and B states, one plate will be metallic
iron and the other iron oxide, with a basic electrolyte.
Each memory cell would be constructed more like a capacitor, but would
be "charged" more like a battery, but with (comparably) very little
capacity. Bits would be stored in the charge-polarity of each cell.
Likewise, for RAM like operation, would likely use a fairly dilute
hydroxide solution (likely much weaker than if it were being used for
energy storage).
Memory cells could be separated either by distance or by an insulating barrier, though potentially the electrolyte reservoir could be shared
between all of the cells (assuming primarily 2 state operation).
For the iron-hydroxide case, the total amount of free oxygen in the
system would likely need to be controlled, so it could not be open to
the atmosphere. If more oxygen could leak in, likely the plates would
turn into ferrate and the electrolyte would turn into water. With any
further oxygen turning the remaining iron into iron-oxide.
Though, charging the cells may drive out the extra oxygen (but, this is
likely to require considerably more power, and if the process goes on
too long, it may structurally damage the cells). Similarly, if the
electrolyte becomes over-saturated with oxygen, then the oxidation
process would resume as soon as power is removed (unless the cells are
charged for long enough for any excess free oxygen to diffuse back out
of the electrolyte).
For a lead-acid chemistry, free oxygen would not matter.
Here iron-iron-hydroxide might be preferable for memory cells, as it
would likely be more stable and have a longer cycle life than a
lead-based design. Cells would likely have a very low energy density,
but this doesn't matter for memory cells (and would be preferable for
RAM like use). One would need a chemistry where cells can be charged in
either direction and which can tolerate cells being rapidly driven from
one polarity to another. Here, less capacity also means less energy
needed to flip a bit (but likely also less stability).
One would also need the wiring to not interact with the electrolyte.
Should probably be able to wire up the cells with a crossbar configuration.
Similarly, the separator would need to be non-reactive with the
electrolyte. More modern materials, like porous plastic or fiberglass
would work. Within the limits of older tech, dunno. cellulose was a
common (such as paper or cotton) but would likely slowly dissolve in the electrolyte solution (I guess, old time solution would probably be to
use asbestos or similar, or maybe a porous ceramic).
For similar reasons, could not use bone or leather/vellum (also weak
against both acids and hydroxides), ...
...
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