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Operating_systems-page63 - Jelena Mamenko Operating Systems...

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Jelena Mamčenko Operating Systems Lecture Notes on Operating Systems 63 40 Cash memory DISK CASHING To help understand the theory of caching, visualize an old, hand-operated water pump. Each stroke of the pump's handle delivers a set amount of water into a glass. It may take two or three handle strokes to fill a glass. Now, visualize several glasses that need to be filled. You are constantly pumping the handle to keep up with the demand. Next, introduce a holding tank. With this, instead of the water going directly into a glass, it goes into the tank. The advantage is, once the holding tank is filled, constant pumping is not required to keep up with the demand. Disk caching may be thought of as an electronic version of a holding tank. With MS-DOS version 5.0, the holding tank is built in with Smartdrv.sys. Cache: A bank of high-speed memory set aside for frequently accessed data. The term " cashing " describes placing data in the cache. Memory caching and disk cashing are the two most common methods used by PCs.
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