A model of Univac 1100/42 swapping

Abstract

The performance of a computer system depends upon the efficiency of its swapping mechanisms. The swapping efficiency is a complex function of many variables. The degree of multiprogramming, the relative loading on the swapping devices, and the speed of the swapping devices are all interdependent variables that affect swapping performance. In this paper, a model of swapping behavior is given. The interdependencies between the degree of multiprogramming, the swapping devices' loadings, and the swapping devices' speeds are modeled using an iterative scheme. The validation of a model is its predictive capability. The given swapping model was applied to a Univac 1100/42 system to predict the effect of moving the swapping activity from drums to discs. When the swapping activity was actually moved, throughput increased by 20%. The model accurately predicted this improvement. Subtopics discussed include: 1) the modeling of blocked and overlapped disc seek activity, 2) the usefulness of empirical formulae, and 3) the calibration of unmeasurable parameters. Extensions and further applications of the model are given.