The system consists of two identical units- Initially one unit is operative and other is kept as spare in cold standby. ¾ A single repair facility is provided to the system for fault detection, repair, replacement and up-gradation purpose of the components. ¾ Upon hardware failure detector check the fault, if detector fails to detect the fault then repairman immediately replaces the failed hardware otherwise unit undergoes for repair. ¾ After failure of initial operative unit the cold standby becomes operative. ¾ If any software component fails then repairman up-grade the software with some up-gradation time. The hardware and software failure time of the unit follows negative exponential distribution while the distributions of repair, fault detection and up-gradation time are taken as arbitrary with different probability density functions