Backward compatibility
The term backward combatible (notice the "b") is sometimes used to describe hardware or software that is designed without regard for compatibility with earlier versions, causing the two versions to fight (or combat) each other. In this case, the two versions cannot share data easily and may have features that cause errors or crashes when they are installed on the same computer, often because the computer does not understand which version is being referred to. Even if the earlier version is removed, remaining vestiges of it may cause problems in running the newer version.