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 the moon. 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.
COS « COSE « COSINE « cosmic rays » COSS »
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