The System Dependability Assessment Tool (SDAT) is an automated tool for analysis of mission critical computer system dependability characteristics. SDAT automatically generates mathematical dependability models based on simple parametric representations of system component characteristics, maintenance and logistics capabilities, subsystem redundancy structures, and critical mission functionality. Detailed mathematical models of various aspects of system dependability behavior can also be constructed, if desired, by the user. SDAT's suite of dependability evaluation capabilities includes a variety of exact and approximate solution techniques that are used to obtain quantitative estimates of component, subsystem, and mission level reliability, maintainability, and availability relative to candidate system designs.