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Definition: Web search engines


A website that maintains an index and short summaries of billions of pages on the Web, Google being the world's largest. China's Baidu, Microsoft's Bing and Yahoo follow in size.

Most search engine sites are free and paid for by ads. Yahoo was the first to gain worldwide attention. Yahoo was originally known as a "directory" rather than a search engine, because it indexed much of its content by human observation. However, as Web content grew exponentially, it became impossible to index everything manually.

Web Spiders, Bots and Crawlers
Most indexing is done automatically by Web "spiders" or "bots," 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 query when you do a search.

Metasearching
"Metasearch" engines search other search engines and bring you results as if you went to each of them independently (see below).

The Deep Web
An enormous amount of content that websites offer resides in databases that are not exposed to the search engines like ordinary HTML pages. This "deep Web," which is much larger than the public Web is accessible only from the website, which may require membership or a paid subscription.

The Portal
Many search engine sites evolved into a portal. Instead of offering content only from other websites, they have their own content and features such as free email, chat rooms and shopping. 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.aol.com (portal)

  www.ask.com

  www.baidu.com (Chinese)

  www.bing.com

  www.excite.com

  www.google.com

  www.hotbot.com

  www.lycos.com

  www.webcrawler.com

  www.yahoo.com (portal)

  www.mamma.com (coupons)

  www.dogpile.com (metasearch)

  www.search.com (metasearch)

  www.wolframalpha.com (computational)