1. Search Engines

2. Search Engines
A search engine is an information retrieval system designed to help find information stored on a computer system.
A Web search engine is a search engine designed to search for information on the World Wide Web.

3. Search Engines
Unlike Web directories, which are maintained by human editors, search engines operate algorithmically or are a mixture of algorithmic and human input. (algorithm)

4. Search Engines
When you do what is called "searching the Web," you are NOT searching it directly. 
It is not possible to search the WWW directly.  The Web is the totality of the many web pages that reside on computers (called “servers") all over the world.  Your computer cannot find or go to them all directly. 

5. Search Engines
To find information on the hundreds of millions of Web pages that exist, a search engine employs special software robots, called spiders, to build lists of the words found on Web sites. When a spider is building its lists, the process is called Web crawling.

6. Search Engines
Factors that influence results include the size of the database, the frequency of updating, and the search capabilities.

7. Search Engines
There are differences in the ways various search engines work, but they all perform three basic tasks:
They search the Internet based on important “key” words.
They keep an index of the words they find, and where they find them.
They allow users to look for words or combinations of words found in that index.

8. Search Engines Search Engines Results:
Rank items by relevance (Google)
Rank items by popularity
Combination

9. Metasearch Engines
A meta-search engine is a search engine that sends user requests to several other search engines and/or databases and aggregates the results into a single list or displays them according to their source.

10. Metasearch Engines
Metasearch engines enable users to enter search criteria once and access several search engines simultaneously.
Still, even the most basic metasearch engine will allow more of the Web to be searched at once than any one stand-alone search engine. On the other hand, the results are said to be less relevant.

11. Metasearch Engines
Examples:
Vivisimo
Dogpile
Ask
Momma
KartOO
Ixquick