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.

