An analysis of some problems in managing virtual memory systems with fast secondary storage devices

Some of the problems that are expected to be encountered in managing virtual memory systems using the newer-technology secondary storage devices are address. The difficulties that two proposed policies have in choosing the most economical program localities of reference to assign to primary memory are analyzed. K. Koh´s (1981) criterion for examining the cyclic locality interval (CLI) hierarchy of a program and choosing the least-cost pathway is examined. Koh´s criterion is designed for the case of a CLI containing a single inner CLI. The decision to descend the hierarchy is based on the cycle time of the outer CLI. If the outer CLI has two or more inner CLIs, it is possible for Koh´s criterion to indicate that it is more economical to descend to one of the inner CLIs without that actually being the case. Choosing which CLI to descend to requires knowledge of its duration, and this is not generally available to the memory management system. An attempt to use Koh´s criterion with the loop structure of a program in order to reduce space-time execution cost was not successful