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<?xml version="1.0" encoding="ISO-8859-1" standalone="no"?>
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>cosmic rays</title><link rel="stylesheet" href="../../jargon.css" type="text/css"/><meta name="generator" content="DocBook XSL Stylesheets V1.61.0"/><link rel="home" href="../index.html" title="The Jargon File"/><link rel="up" href="../C.html" title="C"/><link rel="previous" href="Core-Wars.html" title="Core Wars"/><link rel="next" href="cough-and-die.html" title="cough and die"/></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">cosmic rays</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="Core-Wars.html">Prev</a><EFBFBD></td><th width="60%" align="center">C</th><td width="20%" align="right"><EFBFBD><a accesskey="n" href="cough-and-die.html">Next</a></td></tr></table><hr/></div><dt><a id="cosmic-rays"/><dt xmlns="" id="cosmic-rays"><b>cosmic rays</b>: <span xmlns="http://www.w3.org/1999/xhtml" class="grammar">n.</span></dt></dt><dd><p> Notionally, the cause of <a href="../B/bit-rot.html"><i class="glossterm">bit rot</i></a>. However,
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this is a semi-independent usage that may be invoked as a humorous way to
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<a href="../H/handwave.html"><i class="glossterm">handwave</i></a> away any minor
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<a href="../R/randomness.html"><i class="glossterm">randomness</i></a> that doesn't seem worth the bother of
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investigating. “<span class="quote">Hey, Eric — I just got a burst of garbage on
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my <a href="../T/tube.html"><i class="glossterm">tube</i></a>, where did that come from?</span>”
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“<span class="quote">Cosmic rays, I guess.</span>” Compare
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<a href="../S/sunspots.html"><i class="glossterm">sunspots</i></a>, <a href="../P/phase-of-the-moon.html"><i class="glossterm">phase of the moon</i></a>.
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The British seem to prefer the usage <span class="firstterm">cosmic
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showers</span>; <span class="firstterm">alpha particles</span>
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is also heard, because stray alpha particles passing through a memory chip
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can cause single-bit errors (this becomes increasingly more likely as
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memory sizes and densities increase).</p></dd><dd><p>Factual note: Alpha particles cause bit rot, cosmic rays do not
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(except occasionally in spaceborne computers). Intel could not explain
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random bit drops in their early chips, and one hypothesis was cosmic rays.
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So they created the World's Largest Lead Safe, using 25 tons of the stuff,
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and used two identical boards for testing. One was placed in the safe, one
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outside. The hypothesis was that if cosmic rays were causing the bit
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drops, they should see a statistically significant difference between the
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error rates on the two boards. They did not observe such a difference.
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Further investigation demonstrated conclusively that the bit drops were due
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to alpha particle emissions from thorium (and to a much lesser degree
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uranium) in the encapsulation material. Since it is impossible to
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eliminate these radioactives (they are uniformly distributed through the
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earth's crust, with the statistically insignificant exception of uranium
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lodes) it became obvious that one has to design memories to withstand these
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hits.</p></dd><div class="navfooter"><hr/><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="Core-Wars.html">Prev</a><EFBFBD></td><td width="20%" align="center"><a accesskey="u" href="../C.html">Up</a></td><td width="40%" align="right"><EFBFBD><a accesskey="n" href="cough-and-die.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Core Wars<72></td><td width="20%" align="center"><a accesskey="h" href="../index.html">Home</a></td><td width="40%" align="right" valign="top"><EFBFBD>cough and die</td></tr></table></div></body></html>
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