The results are presented of an analysis of a probabilistic model of a multiprogrammed computer system with a two-level storage system in which there is sequential dependency of accesses between the devices. Expressions are obtained for the long-run probability that both the CPU and each of the storage devices are busy. Some numerical results are given which quantify the gains in CPU utilization obtainable by multiprogramming in the presence of this type of storage system. © 1973, ACM. All rights reserved.