Simulation models are based on computer programs that emulate the different dynamic aspects of a system as well as their static structure. Transactions (jobs) are generated through a probabalistic process, using random number generators, and their flow through the system generates events such as arrival of a customer at the waiting queue of a server, beginning of service at any given server, end of service and so on. The events are processed according to their order of occurrence in time. Counters accumulate statistics that are used at the end of a simulation run to estimate the values of system performance measures. Several simulation runs are required to generate a sample of adequate size to allow for a statistical analysis to be carried out on the sample. Because of the level of detail generally necessary in simulation models, they are often too expensive to run, develop, and validate. But on the other hand, they allow for the investigation of phenomena at any desired level of detail provided that one is ready to pay for it. For this reason, simulation programs are typically run on powerful workstations or even mainframes.
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