The data to drive the simulation can be generated in several ways. The most common method uses a random-number generator, which is programmed to generate processes; CPU burst times, arrivals, departures and so on, according to probability distributions. The distributions can be defined mathematically (uniform, exponential,poisson) or empirically (Silberschatz et al 2002). If a distribution is to be defined empirically, measurements of the actual system under study are taken. The results define