Fault-tolerance: a methodology for implementing highly dependable systems

Dependability is defined as the trustworthiness of a system such that: reliance may be justifiably placed on the service it delivers and; the system has the ability to provide required service whenever that service is needed. The service delivered by a system is its behavior as perceived by its user(s); a user is another system (human or physical) that interacts with the dependable system. This paper will provide a discussion of fault-tolerance design and validation concepts for achieving high levels of dependability. Although fault-tolerance is most effective when designed into a system from the beginning, this paper will also consider approaches that can be effective in improving the dependability of systems developed from commercial off-the-shelf products.