Search engine and directory
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There are two types of search services – computerized search engines and human developed directories. There is also another category of search service called the meta-search engine. Most of the top search services are hybrids, giving first preference to results delivered from their directory followed by results from the search engine.

In a nutshell, search engines provide computer generated results based upon mathematical algorithms that provide a statistical "relevancy" to the keyword submitted. Directories are built by humans, who review and categorize sites into a hierarchal structure, write or approve submitted descriptions of the site, and determine relevancy to the keywords.

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