A comparative analysis of hardware and software fault tolerance: Impact on software reliability engineering

Today's digital systems are growing increasingly complex, and are being used in increasingly critical functions. The first premise makes them more prone to contain faults, and the second premise makes their failure less tolerable. This widening gap highlights the need for fault tolerant techniques, which make provisions for reliable operation of digital systems despite the presence and occasional manifestation of faults. In this paper we present a brief comparative survey of fault tolerance as it arises in hardware systems and software systems. We discuss logical models as well as statistical models of fault tolerance, and use these models to analyze design tradeoffs of fault tolerant systems. This revised version was published online in June 2006 with corrections to the Cover Date.