28-11-2012, 02:24 PM
Internet
The Internet - Defnition.pdf (Size: 123.31 KB / Downloads: 26)
What is Internet?
The Internet, sometimes called simply "the Net", is a worldwide system of computer
networks - a network of networks in which users from one computer can get information if they
have permission from any other computer and sometimes talk directly to users at other
computers.
It was conceived by the Advanced Research Projects Agency (ARPA) of the U.S.
government in 1969 and was first known as the ARPANet.
The original aim was to create a network that would allow users of a research computer at
one university to be able to "talk to" research computers at other universities. A side benefit of
ARPANet's design was that, because messages could be routed or rerouted in more than one
direction, the network could continue to function even if parts of it were destroyed in the event of
a military attack or other disaster.
Today, the Internet is a public, cooperative, and self-sustaining facility accessible to
hundreds of millions of people worldwide. Physically, the Internet uses a portion of the total
resources of the currently existing public telecommunication networks(PSTN).
Technically, what distinguishes the Internet is its use of a set of protocols called TCP/IP
(Transmission Control Protocol/Internet Protocol).
Two recent adaptations of Internet technology, the intranet and the extranet, also make
use of the TCP/IP protocol.
Internet Application
For many Internet users, electronic mail (e-mail) has practically replaced the Postal
Service for short written transactions. Electronic mail is the most widely used application on the
Net. You can also carry on live "conversations" with other computer users, using Internet Relay
Chat (IRC). More recently, Internet telephony hardware and software allows real-time voice
conversations.
The most widely used part of the Internet is the World Wide Web ("WWW" or "the
Web"). Its outstanding feature is hypertext, a method of instant cross-referencing. In most Web
sites, certain words or phrases appear in text of a different color than the rest; often this text is
also underlined. When you select one of these words or phrases, you will be transferred to the
site or page that is relevant to this word or phrase.
Sometimes there are buttons, images, or portions of images that are "clickable." If you
move the pointer over a spot on a Web site and the pointer changes into a hand, this indicates
that you can click and be transferred to another site.
What is the difference between the World Wide Web and the Internet?
The World Wide Web (The Web) is only a portion of the Internet, but it is the fastest
growing part of the Internet. The Web lets people, organizations and companies publish
information for other people to see. This makes the Web a very useful tool for finding
information on just about any topic.
The Web is a large number of computer documents or "Web pages" that are stored on
computers around the world and are connected to one another using hyperlinks. These Web
pages can be seen by anyone through their computer's "Web Browser," which is the program
you are using now.
A group of Web pages that follow the same theme and are connected together with
hyperlinks is called a "Web site." Web sites and Web pages are written in a coding language
that makes it possible to add pictures, sound and interactivity to plain old text, making people's
reading experience more exciting.
Web Server
A Web server is a program that, using the client/server model and the World Wide Web's
Hypertext Transfer Protocol ( HTTP ), serves the files that form Web pages to Web users (whose
computers contain HTTP clients that forward their requests). Every computer on the Internet that
contains a Web site must have a Web server program.
Two leading Web servers are Apache from Jakarta Tomcat , the most widely-installed
Web server, and Microsoft's Internet Information Server ( IIS ). Other Web servers include
Novell's Web Server for users of its NetWare operating system and IBM's family of Lotus
Domino servers.
Web browsers
Web browsers are the client side mini server(programs) used to explore (to browse) the
Internet. There are many Web browser programs available including Netscape Navigator,
Internet Explorer Mozila FireFox, Google Crome and Opera.
Internet Explorer is the Internet browser made by Microsoft and comes with Windows
operating system.
Web Spiders
Most indexing is done automatically by Web "spiders," which are programs that "crawl"
the Web around the clock looking for all the pages they can find. By following the links from
one page to another, they scour billions of pages and summarize them in massive databases,
which is what you are querying when you use a search engine.