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]