The consistent comparison problem in N -version software

Abstract

Multi-version or N -version programming [5] has been proposed as a method of providing fault tolerance in software. The approach requires the separate, independent preparation of multiple ( i.e. "N" ) versions of a piece of software for some application. These versions are executed in parallel in the application environment; each receives identical inputs and each produces its version of the required outputs. The outputs are collected by a voter and, in principle, they should all be the same. In practice there may be some disagreement. If this occurs, the results of the majority (if there is one) are assumed to be the correct output, and this is the output used by the system.