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What is thrashing?

By Simon Loader

Thrashing happens when a hard drive has to move its heads over the swap area many times due to the high number of page faults. This happens when memory accesses are causing page faults as the memory is not located in main memory.
The thrashing happens as memory pages are swapped out to disk only to be paged in again soon afterwards. Instead of memory access happening mainly in main memory, access is mainly to disk causing the processes to become slow as disk access is required for many memory pages and thus thrashing.

How can an OS reduce the effects of thrashing and improve overall performance?

The OS can reduce the effects of thrashing and improve performance by choosing a more suitable replacement strategy for pages. Having a replacement strategy that does not cause memory areas to be written to disk that have not modified since been retrieved reduces thrashing. Using replacement strategies that allow little used rarely accessed pages to remain in memory while the most required pages are swapped in and out.

About the author: Simon Loader is a UNIX and email specialist who runs Surf, a free IT resource and downloads website, in his spare time . Many of the downloads and articles on Surf created by Simon are featured in technical websites all over the world. To access FREE downloads and information covering several diverse IT topics visit www.surf.org.uk.