In critical applications such as civil aviation and signal control in railway traffic, very high reliability of computer control systems is required. So the dissimilar redundancy technique must be adopted in those systems to replace the similar redundancy technique. Similar redundancy can effectively avoid the noncommon stochastic failures that appear in systems, but for common faults such as errors in hardware design and software coding, it would ruin the whole system. In this paper, we introduce a dissimilar fault-tolerant control computer system with software and hardware in detail. A tool SHDFTA (Software/Hardware Dynamic Fault Tree Analysis) 1.0 combining a reliability analysis methodology-Dynamic Fault Tree Analysis (DFTA) is applied to evaluate the system and illustrate the new reliability brought by the dissimilar redundant technique, and the algorithm of DFTA is also introduced.
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