Availability modeling

Availability, which for years has been a critical design parameter in the defense and aerospace industry, has now become a very important design parameter in the commercial world. System designers must evaluate the availability implications of various architectures along with cost, performance, and other measures. Availability models provide a way to predict and compare the availability of system architectures. Design engineers can use these models for performing front-end design tradeoffs, evaluating product modifications, and selecting maintenance strategies. This article describes some common methods used to evaluate the availability of various architectures, particularly Markov models. It illustrates the methods with a simple computer architecture evaluation and shows how single points of failure tend to drive system availability. Markov models are a very flexible and powerful tool for calculating system availability. They can be reduced to linear equations and solved with most commercial spreadsheets. As availability becomes more important in the commercial marketplace, Markov models are becoming a standard design engineering technique.<>