software rot
<programming> 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"software rot" strikes when a program's assumptions become out of date.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)
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