[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.