What is a search engine?

In general, a search engine is the technology powered by a giant database- compiled by either automatically or by human editors- that is used on the internet by the public to make relevant searches to find items.

The term "search engine" is generally used to describe both "crawler based engines" such as Google and "human edited directories" such as Yahoo! Directory.

There is one other kind of search technology that is worth mentioning- "Hybrid Search Engines".  This kind of engine is powered by both "crawler based engines" and "human powered directories".  MSN search is a good example of this kind of search engine.

Crawler based engines

Crawler- based search engines create their listings automatically.  They "crawl" or "spider" the web, then store data into their huge database for people to search through in the internet.  Following are the major players in crawler based search engines:

  1. Google
  2. Teoma
  3. Yahoo! Search
  4. Alltheweb

There are 3 major components of a crawler based search engine.

Spider- this process is also called as the "crawl".  The spider visits web pages, reads the contents, follows the links that it finds to read more contents.  The spider returns to the site on a regular basis to update the contents.

The Index- (or the catalog) is like a giant book which has a copy of all the web pages that the spider has visited.  The index is a database that gets updated each time the spider visits web pages and updates the content.

The Software- the software powers the actual search process when someone is performing a search.  The better the software, the more relevant searches.

Human powered directories

A human-powered directory is a list of websites compiled manually by humans.  When a site is submitted to the directory, an actual real life person reviews the site and decides whether to add it to the directory or not.  Usually the directory will be divided into multiple categories where all the listings are stored.  When someone searches the engine looks for the relevant categories and lists the sites.  Following are the major Human Powered Directories:

  1. Open Project Directory (DMOZ)
  2. Yahoo! Directory
  3. Looksmart

Following is a list of search engines & directories that are important to the SEO industry:


AOL Search

Ask Jeeves






Netscape Search







Search engine optimization guide

Definition of Search Engines


What is SEO/SEM


Why SEO or SEM


SEO Code of Ethics


SEO Industry News


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