Reliability Versus Safety

Abstract

This paper discusses the impact of computer based control systems on the reliability and safety of the total real-time system. It deals with applications. where safety is of utmost importance, but reliability is also an important goal. Both aspects are fundamental qualities of real-time systems, their tradeoff is discussed.Based on a high level view of the system a quantitative model for an analysis of the impact of the computer system on the reliability and safety of the system is presented This model is applied to different software fault tolerant techniques, the following methods are compared: single version. “2 out of 2”- voting. “2 out of 3”-voting (N-version-programming) and the recovery block technique The degree of correlation between faults is an important parameter of the model Finally the impact of a binary output space, which occurs quite often in safety critical real-time systems, is analysed.