software rot

software rot n.  Term used to describe the tendency of
   software that has not been used in a while to {lose}; such
   failure may be semi-humorously ascribed to {bit rot}.  More
   commonly, `software rot' strikes when a program's assumptions
   become out of date.  If the design was insufficiently {robust},
   this may cause it to fail in mysterious ways.

   For example, owing to endemic shortsightedness in the design of
   COBOL programs, most will succumb to software rot when their
   2-digit year counters {wrap around} at the beginning of the
   year 2000.  Actually, related lossages often afflict centenarians
   who have to deal with computer software designed by unimaginative
   clods.  One such incident became the focus of a minor public flap
   in 1990, when a gentleman born in 1889 applied for a driver's
   license renewal in Raleigh, North Carolina.  The new system
   refused to issue the card, probably because with 2-digit years the
   ages 101 and 1 cannot be distinguished.

   Historical note: Software rot in an even funnier sense than the
   mythical one was a real problem on early research computers (e.g.,
   the R1; see {grind crank}).  If a program that depended on a
   peculiar instruction hadn't been run in quite a while, the user
   might discover that the opcodes no longer did the same things they
   once did.  ("Hey, so-and-so needs an instruction to do
   such-and-such.  We can {snarf} this opcode, right?  No one uses
   it.")

   Another classic example of this sprang from the time an MIT hacker
   found a simple way to double the speed of the unconditional jump
   instruction on a PDP-6, so he patched the hardware.  Unfortunately,
   this broke some fragile timing software in a music-playing program,
   throwing its output out of tune.  This was fixed by adding a
   defensive initialization routine to compare the speed of a timing
   loop with the real-time clock; in other words, it figured out how
   fast the PDP-6 was that day, and corrected appropriately.

   Compare {bit rot}.