Asymmetric memory hierarchies

A study is presented of some of the system implications of memory hierarchies in which the backing or secondary store has a very small read time, relative to both the time required for writing and to the read time of conventional backing storage devices. Several analytic models are introduced, and it is shown that such hierarchies may operate in ways which differ from those of more conventional hierarchies. In particular, it is shown that it may not be necessary to multiprogram in such a situation. In the past, backing storage devices have been roughly symmetric with respect to their read and write times. This situation may not continue, as several devices are currently under development which may have a very small read-time/write-time ratio. This study places particular emphasis on one such system—the RCA read/write holographic optical memory.

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