[1] : Jargon File (4.3.1, 29 Jun 2001)

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   program's assumptions become out of date.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.
   syn. `code rot'. see also link rot.

   for example, owing to endemic shortsightedness in the design of cobol
   programs, a good number of them succumbed to software rot when their
   2-digit year counters underwent 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.


see also:
lose bit rot robust link rot wrap around grind crank 
snarf 

[2] : The Free On-line Dictionary of Computing (27 SEP 03)

software rot
     
         the tendency of software that has not been used
        in a while to fail; 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        when a program's assumptions become out of date.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 shortsightedness in the design of some
        cobol programs, many would have succumbed to software rot when
        their 2-digit year counters wrapped around at the beginning of
        the year 2000.  a related incident made the news in 1990, when
        a gentleman born in 1889 applied for a driver's licence
        renewal in raleigh, north carolina.  the 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 initialisation
        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.
     
        jargon file
     
        2002-02-22
     
     
see also:
bit rot robust r1 grind crank opcodes snarf 
mit pdp-6 jargon file 

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