The Jargon File (version 4.4.7, 29 Dec 2003):

bit rot
 n.

    [common] Also bit decay. Hypothetical disease the existence of which has
    been deduced from the observation that unused programs or features will
    often stop working after sufficient time has passed, even if ?nothing has
    changed?. The theory explains that bits decay as if they were radioactive.
    As time passes, the contents of a file or the code in a program will become
    increasingly garbled.

    There actually are physical processes that produce such effects (alpha
    particles generated by trace radionuclides in ceramic chip packages, for
    example, can change the contents of a computer memory unpredictably, and
    various kinds of subtle media failures can corrupt files in mass storage),
    but they are quite rare (and computers are built with error-detecting
    circuitry to compensate for them). The notion long favored among hackers
    that cosmic rays are among the causes of such events turns out to be a
    myth; see the cosmic rays entry for details.

    The term software rot is almost synonymous. Software rot is the effect,
    bit rot the notional cause.


The Free On-line Dictionary of Computing (30 December 2018):

bit rot
alpha particle
bit decay

    A hypothetical disease the existence of which has
   been deduced from the observation that unused programs or
   features will often stop working after sufficient time has
   passed, even if "nothing has changed".  The theory explains
   that bits decay as if they were radioactive.  As time passes,
   the contents of a file or the code in a program will become
   increasingly garbled.

   People with a physics background tend to prefer the variant
   "bit decay" for the analogy with particle decay.

   There actually are physical processes that produce such
   effects (alpha particles generated by trace radionuclides in
   ceramic chip packages, for example, can change the contents of
   a computer memory unpredictably, and various kinds of subtle
   media failures can corrupt files in mass storage), but they
   are quite rare (and computers are built with error detection
   circuitry to compensate for them).  The notion long favoured
   among hackers that cosmic rays are among the causes of such
   events turns out to be a myth.

   Bit rot is the notional cause of software rot.

   See also computron, quantum bogodynamics.

   [Jargon File]

   (1998-03-15)