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Capacity demands for computer memory are increasing. A multilevel storage system provides an economically feasible solution without seriously affecting the total response time. An M-level storage system is considered in this paper. The capability of a digital computer with a multilevel storage system is best enhanced in a multiprogramming environment. In a high level storage system, determination of a best task switching policy becomes an important consideration. In this paper a queuing network is introduced to describe distribution and flow of tasks in the system. An optimal switching policy is determined in relation to the system's overhead time. It is shown that in heavily CPU-limited cases the determination becomes a very simple one; namely, the best policy is given as the threshold level at which the accumulation of the average access time exceeds the overhead time.
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