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From: dplatt@coherent.com (Dave Platt)
Newsgroups: rec.humor,comp.misc
Subject: Re: Looking for Computer Folklore
Message-ID: <20161@coherent.com>
Date: 7 Feb 89 18:14:21 GMT
References: <1000@taux01.UUCP> <3292@ima.ima.isc.com>
Reply-To: dplatt@coherent.com (Dave Platt)
Followup-To: rec.humor
Organization: Coherent Thought Inc., Palo Alto CA
Lines: 57

There's another great story involving computers-that-have-lights.  This
one involves Ivan Sutherland, co-founder of Evans & Sutherland (the
pioneering computer-graphics firm), developer of Sketchpad (the very
first computer-graphics tablet device, I believe), and winner of the
"Father of Computer Graphics" aware some years ago.

While in college, Sutherland worked with one of the very earliest Von
Neumann architecture (stored-program) computers... I've heard this
specific machine referred to as "THE Von Neumann machine".  This
computer had a very limited amount of memory storage.  Rather than using
ferrite cores, RAM memory, or such modern devices, it used "storage
tubes"... tiny little CRTs similar in operation to the tubes used in
some "storage screen" graphics terminals (anybody used a Tektronix 4010
lately)?  These little devices would store a rectangular array of bits
in each tube.  It was actually possible to SEE the bits by looking at
the phosphor-coated target area in each screen.

One of the disadvantages of this storage technology (aside from low
capacity) is that the tubes have a limited lifetime.  "Burn-in"
eventually occurs (as owners of Tektronix storage scopes can attest) as
the phosphor structure ages and breaks down, and eventually the tubes
must be replaced.

The engineers who maintained this computer had some special-purpose
diagnostic programs, which would run "ripple patterns" through memory
and would look for bit-patterns that weren't stored properly (a similar
test is done when diagnosing memory problems in most computers).  With
the Von Neumann machine, though, it was often possible to identify tubes
that were on the way downhill, simply by looking at the array of tubes
in the cabinet and seeing which ones had a dim or uneven appearance
during the ripple test.

One day, Sutherland [and a cohort, I believe] substituted a program deck
of their own devising for the memory-test deck that the engineers used.
This substitute deck did not run the usual memory test;  instead, it
loaded a certain specific bit-pattern into memory and then halted the
machine.

During the next routine-maintenance period, the engineer reset the
machine, booted the deck, and the program immediately halted.  Puzzled,
the engineer reset and rebooted again, and the same thing occurred.
Suspecting that some portion of memory had failed so completely that the
program could not run, the engineer opened the panel to the storage-tube
rack.

There, shining out at him in carefully-lit bits, was a four-letter word.

A sign soon appeared in the computer room... "Programmers will NOT mess
around with the hardware-diagnostic program decks!"

[Disclaimers: it has been 15 years since I heard this story, so I've
 probably forgotten some of the details and have gotten others wrong.]
-- 
Dave Platt    FIDONET:  Dave Platt on 1:204/444        VOICE: (415) 493-8805
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  USNAIL: Coherent Thought Inc.  3350 West Bayshore #205  Palo Alto CA 94303