cosmic rays

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.