Closure and convergence: a formulation of fault-tolerant computing

The authors give a formal definition of what it means for a system to tolerate a class of faults. The definition consists of two conditions. First, if a fault occurs when the system state is within some larger set and, if faults continue occurring, the system state remains within that larger set. Second, if faults stop occurring, the system eventually reaches a state within the legal set. The authors demonstrate the applicability of the definition for stating and verifying the fault-tolerance properties of a variety of digital and computer systems. Using the definition, a simple classification is obtained of fault-tolerant systems, and methods for the systematic design of fault-tolerant systems are outlined.<>