The Backward compatibility reference article from the English Wikipedia on 24-Apr-2004
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Backward compatibility

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In technology (especially computing), backward compatibility has several related but differing meanings:

We distinguish between binary compatibility and source-compatibility. Binary compatibility means that programs can work correctly with the new version of this library without requiring recompilation. Source compatibility requries recompilation but no changes to the source code.

See also: legacy system, forward compatibility, source-compatibility