Reliability and economic analysis of a computer system with independent hardware and software failures

The object of this study is to establish and analyse a reliability model for a computer system with considerations of independent hardware and software failures. There are two identical units in the system-one is operative and other is kept as spare in cold standby. A single server is available to the system who inspects the unit only at its hardware failure to examine the feasibility of repair. If repair of the defective component is not feasible, it is replaced immediately by new one. However, only replacement of the software is made by new one whenever it fails. The failure time of the unit is exponentially distributed while the distributions of inspection, repair and replacement of the software are taken as arbitrary with different probability density functions. The expressions for some reliability and economic measures of the computer system are derived using semi-Markov process and regenerative point technique. The numerical results for a particular case are also obtained to depict the behaviour of MTSF, availability and profit of the system.