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Computing (FOLDOC) dictionary
cosmic rays
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Notionally, the cause of bit rot. However, this is a
semi-independent usage that may be invoked as a humorous way
to handwave away any minor randomness that doesn't seem
worth the bother of investigating. "Hey, Eric - I just got
a burst of garbage on my tube, where did that come from?"
"Cosmic rays, I guess." Compare sunspots, phase of themoon. The British seem to prefer the usage "cosmic showers";
"alpha particles" is also heard, because stray alpha particles
passing through a memory chip can cause single bit errors
(this becomes increasingly more likely as memory sizes and
densities increase).
Factual note: Alpha particles cause bit rot, cosmic rays do
not (except occasionally in spaceborne computers). Intel
could not explain random bit drops in their early chips, and
one hypothesis was cosmic rays. So they created the World's
Largest Lead Safe, using 25 tons of the stuff, and used two
identical boards for testing. One was placed in the safe, one
outside. The hypothesis was that if cosmic rays were causing
the bit drops, they should see a statistically significant
difference between the error rates on the two boards. They
did not observe such a difference. Further investigation
demonstrated conclusively that the bit drops were due to alpha
particle emissions from thorium (and to a much lesser degree
uranium) in the encapsulation material. Since it is
impossible to eliminate these radioactives (they are uniformly
distributed through the earth's crust, with the statistically
insignificant exception of uranium lodes) it became obvious
that one has to design memories to withstand these hits.