On Approximate Computer System Models

A new treatment of the boundary conditions of diffusion approximations for interconnected queueing systems is presented. The results have applications to the study of the performance of multiple-resource computer systems. In this approximation method, additional equations to represent the behavior of the queues when they are empty are introduced. This reduces the dependence of the model on heavy traffic assumptions and yields certain results which would be expected from queueing or renewal theory. The accuracy of the approach is evaluated by comparison with certain known exact or numerical results.