If you are not careful, you will be buried in hits. Metasearch engines send your search to several databases and search engines at once and then give you the results. These engines only allow very simple searches and give very broad results. The big advantage of metasearch engines is that they allow you to search a larger percentage of the entire Web. A metasearch engine employs several individual engines.
Subject directories base their searches on context analysis, usually by actual humans.
Sites are categorized and pre-grouped so that you can work your way down from most general to most specific subject headings. Specialized search engines focus on just one or two areas of interest. For example, WhoWhere specializes in helping you find people, DejaNews focuses on Usenet Newsgroups. Knowing about specialized search engines can be extremely valuable if there is one in the area in which you are doing research. For more information, try the links listed below.