Models for Time-Sharing Computer Systems with Heterogeneous Users

Models for time-sharing computer systems are presented. The models are of the repairman type and involve more than one type of customer demanding service from a single server queue. The models studied do not admit a product form stationary distribution, thus approximation methods designed to study the queue length processes are introduced. Of particular importance is the introduction of an approximation method which allows for the queue discipline to be varied parametrically. The associated diffusion approximation allows one to study system performance as a function of queue discipline.