Improving the Reliability of Digital Devices with Redundancy: An Application of Decision Theory

The reliability of complex digital systems can be increased by increasing the reliability of the components of the system or by inserting redundant components into the system. Since it is often prohibitively expensive to obtain successively higher levels of component reliability, inserting redundant components may be the only reasonable way to satisfy future digital system requirements. The reliability of a given computer subsystem may be improved by adding redundant subsystems of the same sort having the same inputs, and entering the several outputs into a decision element designed to produce the most probably, correct final output. This paper deals with designing the decision element. The optimum design is obtained for several different types of systems. The decision element that maximizes the ``reliability'' is derived when the a priori probabilities of various outputs are known and when they are unknown. The optimum element is unique when the a priori probability is unknown.