Primary Computer Storage

Abstract

In the buffer models that were analyzed previously, the storage device was assumed to be depleted at a constant rate when nonempty. This assumption is unsuitable for modeling such systems as computer memories, in which several new features appear. For example, the length of time a program stays in memory, i.e., its execution time, may be correlated with its size, and it may be increased because of other programs that are competing for the processor. Also, the item stored, typically a data set or a program to be executed, retains its identity in the sense that departing items and their sizes are in an obvious one-to-one correspondence with arriving items and their sizes. This “conservation principle” presents a major difficulty in the analysis, for in many Markov models it means that we have to carry along as part of the state variable an indication of the size of each item in memory. These have been termed models of “exact content” by Beneŝ [Ben1].