backward combatability

/bakw@rd k@mbat'@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.

