Software fault-tolerance and design diversity : past experience and future evolution

Interest in software fault-tolerance (following an interest in fault-tolerance in general, and prompted by the so called "software crisis") is now exhibited by many institutions. Though many software fault-tolerance techniques are known, their use is limited by the lack of consistent, flexible methodologies, of support mechanisms in operating systems and of design tools. In this paper, we discuss the known software fault-tolerance techniques, with particular reference to the two coherent methodologies proposed, Multiple Version Software and Recovery Blocks. We argue that a more general methodology is needed for use in complex software system, and outline how the necessary mechanisms could be included in low-level system software.