backward combatability: /bak'w*rd k*m-bat'*-bil'*-tee/ n. [CMU,
Tektronix: from `backward compatibility'] A property of hardware or
software revisions in which previous protocols, formats, layouts,
etc. are irrevocably discarded in favor of `new and improved'
protocols, formats, and layouts, leaving the previous ones not
merely deprecated but actively defeated. (Too often, the old and
new versions cannot definitively be distinguished, such that
lingering instances of the previous ones yield crashes or other
infelicitous effects, as opposed to a simple "version mismatch"
message.) A backwards compatible change, on the other hand, allows
old versions to coexist without crashes or error messages, but too
many major changes incorporating elaborate backwards compatibility
processing can lead to extreme software bloat. See also flag
day.
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