A search engine operates, in the following order.

Crawler-Based Search Engines
Google is one of the examples of Crawler-based search engines which have it own listings, and they will ‘crawl’ and use the software ‘spider’ to search the web.
The main characteristic of Crawler Based-Search Engines will make changes on their findings whenever the authors change his web pages.
How does Crawler-Based Search Engine work?
Crawler-based search engines have three major elements, namely, the ‘Spider, the ‘Index’ and the ‘Search Engine’.

1.The Spider

The Spider visit a web page, reads it, and follow links on the site to other pages. Visited sites would be checked on a regular basis, such as a month or two, to look for changes.

2.The Index

Spider web page comes to the index, where the data are copied and stored in. Every web page the spider visited would be indexed. And new information is updated in index whenever the web pages changes.

3 .Search Engine

This is the programmer that surf through the millions pages data in the index to find matches to a search and rank them in order of relevance. Some web page may not be displayed if it is only spider but not index.

Major Search Engines: The Same, But Different

Most of the search engines have the same function. But people may ask why the same search on different search engines often displays different results? This is because there are differences in how these parts (for example their crawler programme is different and their catalog is not the same) are tuned. Therefore some of the search engines may list different results.

 

 

The references of sources are come from

http://www.helium.com/items/489328-search-engines-playing-pivotal
http://searchenginewatch.com/showPage.html?page=2168031
http://cobaltsystems.com/advice/search_stats.html