A Three-Failure-Tolerant Computer System

Two basic factors influence the design of highly reliable computer systems: the amount of failures required to be tolerated and the reliability or MTBF required. A computer system designed to tolerate any three single failures in a fail-operational–fail-operational–fail-safe manner for a real-time control application is presented. The design approach uses adaptive majority voting in both hardware and software with a four-level redundant system. Various methods of performing the adaptive majority voting functions were evaluated with the selected approach using a special module termed a voter–comparator switch (VCS). The VCS module allows the computer system to be operated in a variety of redundant modes, depending on the failure tolerance required at any particular time.