Analysis of a Cold Standby Computer System with Arrival Time of the Server at S/w Failure and Priority for S/w Up-Gradation over H/w Repair

ABSTRACT The purpose of this paper is to examine the behaviour of some important performance measures of a computer system with the concepts of cold standby redundancy, arrival time of the server and priority for s/w up-gradation. A reliability model is developed in which two identical units of a computer system are taken up- one unit is initially operative and the other is kept as spare in cold standby. In each unit h/w and s/w work together and may fail independently from normal mode. There is a single server who visits the system immediately at h/w failure while some arrival time is given to him at s/w failure. Server repairs the unit at h/w failure; whereas s/w is upgraded from time to time when it fails to execute the programs properly. Priority to s/w up-gradation is given over h/w repair in case one unit is under repair due to h/w failure and other unit fails due to s/w. All random variables are assumed as statistically independent. The time to h/w and s/w failures follows negative exponential while the distributions of h/w repair time, s/w up-gradation time and arrival time of the server are taken as arbitrary with different probability density functions. The expressions for various performance measures are derived in steady state using semi-Markov process and regenerative point technique. Graphs are drawn to depict the behaviour of some performance measures such as MTSF, availability and profit function giving particular values to several parameters and costs. Keywords: Computer System, H/w Repair, S/w up-gradation, Arrival Time and Priority.