Individual search engines use complex algorithms based on a site's information and HTML code to rank sites. Google is an example of a pure search engine site. Directories are the second type of search site. To get listed on a directory, you must submit your front page on the directory's submission form. Unlike pure search engines, directories don't automatically add sites.
Human reviewers check every submission to decide if it's appropriate for the directory.
The Open Directory is an example of an Internet directory. Most of the major search sites on the Internet today combine search engine and directory functionality. Major search engines like AltaVista , Excite , Lycos , HotBot , and Infoseek all have some form of directory associated with them. If no results from their human-edited directories match your search query, then their search engines search through a database of spidered sites to give you results. Web Pages provides spidered results.