Journal of the ACM (JACM)
ACM Computing Surveys (CSUR)
A Note on Paging Drum Efficiency
ACM Computing Surveys (CSUR)
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The efficiency of a paging drum, operating as the back-up storage device in a virtual memory system, is defined to be the percentage of time that data is being transferred. Efficiency (E) is a function of the number of page requests pending (L), and the capacity of one track on the drum (S), expressed as a multiple of the page size. Denning has derived the following formula E(L) &equil; 2•L/(2•L+s−1). This formula is shown to be a very accurate predictor of paging drum efficiency. Denning has also derived results for the space-time cost of loading a program's working set using the strategies of prepaging and pure demand paging. For the cost of prepaging, simulation analysis produces results which are at variance with those predicted by the analytically derived formula. The simulated cost of prepaging the working set is tabulated for several values of L, s, and w (the number of pages in the working set), and compared with the cost of loading the working set by pure demand paging.