System Effectiveness as a Generalization of System Availability

This paper discusses certain concepts and sample results in the techniques of system effectiveness analysis with particular attention to availability. It turns out that the contemporary concept of system effectiveness can be usefully viewed as a generalization of prior concepts relating to system availability. Central to the paper´s approach is a presentation of the need for redefinition of system availability. While on the one hand some 18 definitions are available in the literature, this latter concept is not broad enough for complex systems; the implied binary situation of a system being either UP or DOWN is not an accurate enough model for such systems. System effectiveness, which has been evolved to replace availability, arises from attempts to unify treatment of the statistics of system state behavior and transition behavior, of the performance capability associated with these states and transitions, and of the interaction of the performance statistics within the conditions of the problem. The analytic techniques developed are of particular power when dealing with redundant and modular systems. A comparative effectiveness evaluation of 10 alternative computer system designs, all having the same basic performance, is exhibited; this analysis was performed with respect to a given sample functional requirement.