This paper presents a simple mathematical model for system reliability calculation. N-version programming and recovery block are fault-tolerant architectures that have taken into account for hardware and software fault tolerant system design. Each of the architectures has different characteristics for use in the real world system. Our work is extended from a work of Laprie et al where definition and analysis of multi-version hardware and software fault-tolerant system reliability was defined and from our previous work where the system reliability analysis is complex to be extended to higher degree of fault tolerance. Possible failures in the system are considered including decider failure, related fault between/among software versions, and related fault between decider and software versions. This model is easy to calculate and be extended to higher degree of fault tolerance with consideration of all possible causes of system failure.
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