Subject directories, such as Yahoo, depend on humans for their listings. Directories are compiled based on descriptions of web sites and listed under one or more subject categories. Directories are a good place to start when looking for information on relatively general subjects and to get an overview of what is available on the Internet in almost any subject area.
Directories find fewer but often more relevant sites than search engines.
Since search engines are different in size, search features, and the criteria of documents indexed, the same search on different engines often produces different results. The results are catagorized by each search engine. Since each search engine includes a differenct set of sites, mega-search engines are recommended in order to perform the most extensive search possible. Another useful source is the California State Library's InFoPeople Project , which maintains a site detailing major search engines. A directory of quality academic oriented Web sites that are intended for an audience at the undergraduate level.