[GTALUG] CRT memories [was Re: IBM - cache skirmish story.]

D. Hugh Redelmeier hugh at mimosa.com
Tue Apr 24 15:10:06 EDT 2018

I forgot to mention the amazing plasma technology invented at
University of Illinois for the Plato project.


First, lets think of a neon tube.  It gets turned on when a high
voltage is applied.  With no voltage, no light.  But once it has
started, an intermediate voltage can maintain the light.  If it
hasn't started, that voltage will leave the tube off.  So, powered by
that voltage, the tube is a memory.  You can tell its state by the
amount of current it draws.

Same with pixels on a plasma display.  So each pixel is its own memory
and no refresh is needed.

I first saw a Plato terminal when CDC (a mainframe computer company
which had commercial rights to Plato) loaned a few Plato terminals to
University of Waterloo for a summer (1972?).

(Some old devices did use neon tubes as memories (and not displays).
One bit per tube.  One example: the IBM 407 accounting machine.)

These things were way in advance of other technology.  I don't know
why they didn't take over the world.  Perhaps they were expensive.


Another technology that I did not mentioned: Williams Tube memories.
These are CRTs but they were used as memories, not displays.  So they
are a bit off topic.

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