Reliability and Availability Models for Maintained Systems Featuring Hardware Failures and Design Faults

Modeling of systems featuring hardware and software faults is studied as a means of evaluating the availability and reliability characteristics. The case of a nonredundant computer is studied and it is shown that the unavailability presents an overshoot with respect to its asymptotic value whose height and length are functions of the failure rates associated with the different design errors. Fault-tolerant systems are studied that include protective redundancies both at the hardware level and at the software level; the importance of homogeneous solutions on both levels is shown.