By John G. Williams
Communications of the ACM,
March 1971,
Vol. 14 No. 3, Pages 172-175
10.1145/362566.362570
Comments
The utilization of storage is studied in a two-level memory hierarchy. The first storage level, which is the fast store, is divided into a number of storage areas. When an entry is to be filed in the hierarchy, a hashing algorithm will attempt to place the entry into one of these areas. If this particular area is full, then the entry will be placed into the slower second-level store, even though other areas in the first-level store may have space available. Given that N entries have been filed in the entire hierarchy, an expression is derived for the expected number of entries filed in the first-level store. This expression gives a measure of how effectively the first-level store is being used. By means of examples, storage utilization is then studied as a function of the hashing algorithm, the number of storage areas into which the first-level store is divided and the total size of the first-level store.
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