Indexes

Most search engines, including Google (by far the most popular), are index-based. Internet users like them because they return a large number of accurate results quickly.

Before a search engine can find web pages and files, it must first search the Web to locate and index all the data that's out there. A search engine accomplishes this with sophisticated software robots called "spiders," which scour web servers to search for web pages and links to yet more web pages. Spiders record all the words they find, creating a massive set of keywords that are then written to the search engine's database.Directories. With directories, the search engine user compromises a bit of comprehensiveness for better organized and fewer irrelevant search results.

Directories are compiled by people based on websites that are submitted to their directories by website creators. Yahoo!'s directory is a good example of directory-based search engine.

Some search engines, called meta-search engines, are designed to solely to search the results of other search engines. These are powerful tools when you want complete search results, especially when trying to uncover difficult-to-find information. The most-popular meta-search engines include Dogpile (http://www.dogpile.com), Mamma (http://www.mamma.com) and Metacrawler (http://www.metacrawler.com).