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.
    

cosmic rays

   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.

   [{Jargon File}]