cosmic rays

n. 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.

