26 lines
1.6 KiB
Plaintext
26 lines
1.6 KiB
Plaintext
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.
|
|
|