Reliability Modelling of a Computer System with Priority to H/W Repair over Replacement of H/W and Up-gradation of S/W Subject to MOT and MRT

In the present paper, some reliability measures of a computer system of two cold standby identical units are obtained using a semi-markov process and a regenerative point technique. for this purpose, a reliability model is proposed by considering independent h/w and s/w failure. initially, one unit is operative and another is kept as spare in cold standby. a single server is provided to conduct preventive maintenance, repair, replacement and up-gradation of the components upon their failure. then, a maximum operation time system undergoes preventive maintenance, directly from normal mode. if the repair of the h/w is not possible by the server up to a pre-specific time, it is replaced by a new one with some replacement time. however, only up-gradation of the software by a new one is made whenever s/w fails to execute the desired function properly. priority to h/w repair is given over h/w replacement and s/w up-gradation. the failure time distribution of the h/w and s/w follows a negative exponential while the distributions of preventive maintenance, repair, up-gradation and replacement time are taken as arbitrary with different probability density functions. to depict the importance of the study, graphs are drawn for a particular case with fixed values of other parameters and costs.