For an explanation of how those features work and how you can use them to find the information you want, keep reading. Although there are several types of Web search services and each seems to give you access to nearly everything imaginable, no service can index the entire Web. The World Wide Web has perhaps a half a billion pages of information, and the largest search engines can find fewer than half of them. In fact, when you perform a search online, you are actually searching the index made by the search service, not the Web itself. The larger search engines will be more helpful when you want to find somewhat obscure information or a site off the beaten path, but smaller sites will give you more focused results when you're mainly interested in large, common, or popular sites.
Most services use both a human-compiled directory and a search engine.
Both types of services have their advantages. Directories are usually categorized and reviewed, but true search engines usually have larger indexes and can return a broader range of results. A third type of search service is called a metacrawler. Metacrawlers can find more information than a single search engine, but be warned that since each search engine treats your query a bit differently, the usefulness of your results may vary. Three ways to search When you enter a string of words, a search engine can treat them in three ways.