Microcomputer system reliability using triple-modularredundancy (TMR) is discussed when failures exist not only in any single module but also in any two or three modules at a time. The optimal time interval is calculated by which the system will even be resynchronized periodically so that additional transient failures can be tolerated. It is shown that in spite of the optimal resynchronization, thereliability of the system cannot be improved by the ordinary TMR under some dependent-failures. For the purpose of eliminating the effect of dependent-failures, a new fault-tolerant microcomputer system is proposed where a program is executed three times by three CPU's.
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