STOCHASTIC MODELING OF A COMPUTER SYSTEM WITH PRIORITY TO UP-GRADA TION OF SOFTW ARE OVER HARDWARE REPAIR ACTIVITIES

This paper concentrates on the stochastic modeling of a computer system in which software and hardware components have direct independent failure from normal mode. In this model, two identical units of a computer system are taken together in which one unit is initially operative and the other is kept as cold standby. There is a single server who visits the system immediately to carry out inspection, h/w repair activities and s/w up-gradation. The unit undergoes for inspection at its hardware failure to see the feasibility of repair. If repair of the hardware in the unit is not feasible, it is replaced by new one with some replacement time. However, if there is a software failure in the unit, then only up-gradation of the software is made with some up-gradation time. Also, priority to s/w up-gradation is given over h/w inspection and repair. The distributions of failure time of hardware and software follow negative exponential while that of inspection, s/w up-gradation and h/w repair times are taken as arbitrary with different probability density functions (pdf). Various reliability measures are obtained by adopting semi-Markov process and regenerative point technique. The results for a particular case are also evaluated to depict the graphical behavior of some measures of system effectiveness.