Processing Queries
When the search engine receives a request, the engine retrieves from its index all documenta matching the request. A match is determined if the phrase or keyword is found on a page in the index database. An example is, a search for Computer and programming magazine at Yahoo returns 4.00 million results, but a search for the same phrase in quotes ("Computer and programming") returns only 50 thousand results. In the first case, Yahoo returned all documents which had the terms "Computer", "programming", and "magazine" (the "and" is ignored because it's not essential to the results), however in the second case, only those pages with the exact phrase "Computer and programming magazine" were returned.

Crawling the Web
Search engines use "bots" or "spiders" which are automated programs, that use the hyperlink structure of the web to "crawl" the pages and documents that make up the World Wide Web. Search engines have estimated to have crawled 40%-50% of all web pages

Indexing Documents
When a page has been crawled, its contents are "indexed", which means that the information for the page is stored in a huge database of documents making up a search engine's "index". This index is managed very efficiently, since millions of request from users on the internet will result in the access of documents in this index. This documents must be accessed with in fractions of a second to provide almost instant response to the user.

Ranking Results
Once the search engine has determined which results are a match for the query, the engine's algorithm (a mathematical equation commonly used for sorting) runs calculations on each of the results to determine which is most relevant to the given query. They sort these on the results pages in order from most relevant to least so that users can make a choice about which to select. Although a search engine's operations are not particularly lengthy, systems like Google, Yahoo! and MSN are among the most complex, processing-intensive computers in the world, managing millions of calculations each second and funneling demands for information to an enormous group of users.