The person charging this material is responsible for its renewal or its return to the library from which it was borrowed on or before the Latest Date stamped below. The Minimum Fee for each Lost ABSTRACT With the advent of network computers, a new area of computer systems analysis has evolved. Unfortunately, most of the work which has been done to date merely extends the previously existing theory of communications. While this work has been very fruitful and produced important results, our analysis is predicated on the assumption that a geographically distributed network computer is, in reality, quite different from telephone networks and individual computing centers. In this paper, we focus our attention on the probable goals of the networks and define a measure of cost effectiveness. Then using this measure we develop a priority assignment technique for the individual centers that comprise the network. We conclude by expanding the measure of cost effectiveness to determine load leveling rules for the entire network.

In this paper we present some results obtained from using simulation as a tool for evaluating alternative methods of improving system performance in network computers. We begin by describing a GPSS model which was developed to evaluate the current computer center operations at the University of Illinois. While using actual data from the center to verify that the rriodel accurately predicts each job's total time in the system, we evaluate the resource utilization within the center. Then we use the simulator to show that a proposed dynamic priority assignment algorithm yields better throughput than the existing algorithm while maintaining a higher level of CPU and memory utilization. Next, turning our attention to a hypothetical network of three centers, we use a generalization of our model to demonstrate the effects of load leveling between tenters on the total system throughput. Here we also explore the merits of "-pay-for-priority" schemes in both a single center and in a network of three centers.

Network computers are becoming a reality in the seventies. While systems such as the ARPA network, Carnegie Mellon's PLN, the Collins C-System, CDC's Cybernet, and GE's Time Share Net are coming to fruition, even more grandiose systems are being discussed. These networks all offer the designer the potential of combining the advantages of data base sharing, resource sharing, and load leveling with those of message switching. From a postulation of the essential characteristics of a network computer currently under development, we formulate a queueing theory model for a multiserver system with a finite length priority queue. Then, under the assumptions of Poisson input and exponentially distributed processing times, we use this idealized mathematical model to investigate the steady state stochastic behavior of Jobs in the network. We are particularly interested in the efficiency of computer utilization and the average waiting time for Jobs of different priority classes.