Web search engines - technical definition

A Web site that maintains an index and short summaries of billions of pages on the Web, Google being the world's largest. Most search engine sites are free and paid for by advertising banners, while others charge for the service. Yahoo! was the first search engine to gain worldwide attention, and it initially indexed most of its content manually, creating a hierarchical directory that was put together by human observation. It was known then as a "directory" rather than a "search engine." However, as Web content grew exponentially, it became impossible to index everything manually.

Web Spiders
Most indexing is done automatically by Web "spiders," which are programs that "crawl" the Web around the clock looking for all the pages they can find. By following the links from one page to another, they scour billions of pages and summarize them in massive databases, which is what you are querying when you use a search engine.

Metasearching
"Metasearch" engines are search engines that search other search engines and bring you results as if you had made the effort to search all those sites independently (see list below).

Deep Web Searches
An enormous amount of content that Web sites offer to visitors resides in databases that are not exposed to the world at large as are HTML pages with links to each other. This is known as the "deep Web." Some search engine sites offer deep Web content as well (see list below).

The Portal
Many search engine sites evolved into a portal. Instead of offering content only from other Web sites, they have their own content and features such as free e-mail, chat rooms and shopping. For information about all major search engines, visit www.searchenginewatch.com. See portal, Web white pages, Web yellow pages and information broker.

Search Engine Sites

Following are popular sites for searching any topic. If you do not find what you want at one site, try another, even if you use a metasearch engine. Spiders do not always find the same information at the same time.

     www.altavista.com
     www.ask.com
     www.excite.com
     www.go.com
     www.go2.com
     www.google.com
     www.hotbot.com
     www.lycos.com
     www.northernlight.com
     www.opentext.com
     www.rocketnews.com (recent news only)
     www.webcrawler.com
     http://vivisimo.com

     www.lexibot.com         deep Web
     www.quigo.com           deep Web

     www.about.com           directory
     www.suite101.com        directory
     www.yahoo.com           directory

     www.a9.com              metasearch
     www.dogpile.com         metasearch
     www.go2net.com          metasearch
     www.mamma.com           metasearch
     www.search.com          metasearch

     www.wolframalpha.com    computational