High reliability systems have to work no matter what. A common method of combating down time is to duplicate some of the vital circuitry so the system can detect any single type of failure mode. With this capability, a system could either switch between the duplicate circuits, or behave in a different way that is appropriate when a failure is detected. By implementing the redundant device based on a very different technology, with differing failure modes and fault conditions for the redundant circuitry, this possibility can be alleviated. This paper looks at design diversity and demonstrates the technology used from one generation to the next is often revolutionary and has no bearing on old design techniques.