Search engines Vs web directories

"Search engine" and "Web directory" are two different search services available to the Web community. Search engines have indices that are built up by robots or crawlers; whereas Web directories build up their indices through human editors. Many search engines and directories contain both a computer-generated index and a human generated index, and are referred to as hybrids.

Google, Inktomi, AltaVista, AlltheWeb and the like are all forms of search engines. These search engines write programs known as robots, crawlers and/or spiders that have the following functions: (1) to locate Web pages, (2) to read the contents of the Web pages and (3) report its findings back to the search engine's indices or databases. Many search engines update their index either on a bi-monthly or monthly basis. When Web searchers use a search engine to locate Web sites that are relevant to the keyword search, they are searching the search engine's index. A search engine with a larger and more up-to-date index is a better representation of the information available in the Web.

The term "search engine" is often used generically to describe both crawler-based search engines and human-powered directories. These two types of search engines gather their listings in radically different ways.