Radiation and Computers

["Ralph NORTH" <Ralph.North@ccmail.adp.wisc.edu>]

     Excerpted from comp.sys.ibm.pc.hardware FAQ:
     
     SOFT ERRORS occur when one or more bits in a memory read back
     different data than was written to them, BUT after rewriting the same
     data the memory reads it back correctly.  In other words: the error is
     transient and not reproducible.  Soft errors are usually intermittent
     with anywhere from hours to years between occurrences.  There are two
     design causes for soft errors, motherboard noise and internal DRAM
     noise due to alpha particles or marginal circuits.  On a well designed
     motherboard, noise does not cause measurable soft errors unless the
     board is defective.
     
     ALL DRAM PRODUCES SOFT ERRORS DUE TO ALPHA PARTICLES.  The plastic
     packaging of the DRAM contains small amounts of radioactivity that
     produce alpha particles.  These are energetic, fast moving, helium
     atoms which are missing their electrons.  When an alpha particle
     emitted by the packaging hits a sense line in the DRAM during a read
     cycle, the noise it produces causes the sense amplifier to misread the
     data.  Then, as with all DRAM, the memory cell is refreshed after
     reading and the bad data becomes permanent.