Software rot

Software rot, also known as code rot, bit rot, software erosion, software decay or software entropy describes the perceived "rot" which is either a slow deterioration of software performance over time or its diminishing responsiveness that will eventually lead to software becoming faulty, unusable, or otherwise called "legacy" and in need of upgrade. This is not a physical phenomenon: the software does not actually decay, but rather suffers from a lack of being responsive and updated with respect to the changing environment in which it resides.

The Jargon File, a compendium of hacker lore, defines "bit rot" as a jocular explanation for the degradation of a software program over time even if "nothing has changed"; the idea being this is almost as if the bits that make up the program were subject to radioactive decay.

Software can deteriorate in performance over time, which is commonly called aging, as it runs and accumulates errors; this is not generally considered software rot, though it may have some of the same consequences. Usually, such a degraded state can be remedied by completely reinitializing its state (as by a complete reinstallation of all relevant software components, possibly including operating system software); this may also remedy some kinds of software rot, whereas other software rot is irreversible, as the operating environment of the software, or components of the software itself being incompatible, and hence becoming legacy.

Several factors are responsible for software rot, including changes to the environment in which the software operates, degradation of compatibility between parts of the software itself, and the appearance of bugs in unused or rarely used code.

When changes occur in the program's environment, particularly changes which the designer of the program did not anticipate, the software may no longer operate as originally intended. For example, many early computer game designers used the CPU clock speed as a timer in the game, but newer CPU clocks were faster, so the gameplay speed increased accordingly, making the game less usable over time.

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