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Aperçu du corrigé : Internet.

Publié le : 11/5/2013 -Format: Document en format HTML protégé




Internet, computer-based global information system. The Internet is composed of many interconnected computer networks. Each network may link tens, hundreds, or
even thousands of computers, enabling them to share information and processing power. The Internet has made it possible for people all over the world to
communicate with one another effectively and inexpensively. Unlike traditional broadcasting media, such as radio and television, the Internet does not have a
centralized distribution system. Instead, an individual who has Internet access can communicate directly with anyone else on the Internet, post information for general
consumption, retrieve information, use distant applications and services, or buy and sell products.
The Internet has brought new opportunities to government, business, and education. Governments use the Internet for internal communication, distribution of
information, and automated tax processing. In addition to offering goods and services online to customers, businesses use the Internet to interact with other
businesses. Many individuals use the Internet for communicating through electronic mail (e-mail), retrieving news, researching information, shopping, paying bills,
banking, listening to music, watching movies, playing games, and even making telephone calls. Educational institutions use the Internet for research and to deliver
online courses and course material to students.
Use of the Internet has grown tremendously since its inception. The Internet's success arises from its flexibility. Instead of restricting component networks to a
particular manufacturer or particular type, Internet technology allows interconnection of any kind of computer network. No network is too large or too small, too fast or
too slow to be interconnected. Thus, the Internet includes inexpensive networks that can only connect a few computers within a single room as well as expensive
networks that can span a continent and connect thousands of computers. See Local Area Network.
Internet service providers (ISPs) provide Internet access to customers, usually for a monthly fee. A customer who subscribes to an ISP's service uses the ISP's network
to access the Internet. Because ISPs offer their services to the general public, the networks they operate are known as public access networks. In the United States, as
in many countries, ISPs are private companies; in countries where telephone service is a government-regulated monopoly, the government often controls ISPs.
An organization that has many computers usually owns and operates a private network, called an intranet, which connects all the computers within the organization. To
provide Internet service, the organization connects its intranet to the Internet. Unlike public access networks, intranets are restricted to provide security. Only
authorized computers at the organization can connect to the intranet, and the organization restricts communication between the intranet and the global Internet. The
restrictions allow computers inside the organization to exchange information but keep the information confidential and protected from outsiders.
The Internet has doubled in size every 9 to 14 months since it began in the late 1970s. In 1981 only 213 computers were connected to the Internet. By 2000 the
number had grown to more than 400 million. The current number of people who use the Internet can only be estimated. Some analysts said that the number of users
was expected to top 1 billion by the end of 2005.



Before the Internet was created, the U.S. military had developed and deployed communications networks, including a network known as ARPANET. Uses of the networks
were restricted to military personnel and the researchers who developed the technology. Many people regard the ARPANET as the precursor of the Internet. From the
1970s until the late 1980s the Internet was a U.S. government-funded communication and research tool restricted almost exclusively to academic and military uses. It
was administered by the National Science Foundation (NSF). At universities, only a handful of researchers working on Internet research had access. In the 1980s the
NSF developed an "acceptable use policy" that relaxed restrictions and allowed faculty at universities to use the Internet for research and scholarly activities. However,
the NSF policy prohibited all commercial uses of the Internet. Under this policy advertising did not appear on the Internet, and people could not charge for access to
Internet content or sell products or services on the Internet.
By 1995, however, the NSF ceased its administration of the Internet. The Internet was privatized, and commercial use was permitted. This move coincided with the
growth in popularity of the World Wide Web (WWW), which was developed by British physicist and computer scientist Timothy Berners-Lee. The Web replaced file
transfer as the application used for most Internet traffic. The difference between the Internet and the Web is similar to the distinction between a highway system and a
package delivery service that uses the highways to move cargo from one city to another: The Internet is the highway system over which Web traffic and traffic from
other applications move. The Web consists of programs running on many computers that allow a user to find and display multimedia documents (documents that
contain a combination of text, photographs, graphics, audio, and video). Many analysts attribute the explosion in use and popularity of the Internet to the visual nature
of Web documents. By the end of 2000, Web traffic dominated the Internet--more than 80 percent of all traffic on the Internet came from the Web.
Companies, individuals, and institutions use the Internet in many ways. Companies use the Internet for electronic commerce, also called e-commerce, including
advertising, selling, buying, distributing products, and providing customer service. In addition, companies use the Internet for business-to-business transactions, such
as exchanging financial information and accessing complex databases. Businesses and institutions use the Internet for voice and video conferencing and other forms of
communication that enable people to telecommute (work away from the office using a computer). The use of e-mail speeds communication between companies, among
coworkers, and among other individuals. Media and entertainment companies run online news and weather services over the Internet, distribute music and movies, and
actually broadcast audio and video, including live radio and television programs. File sharing services let individuals swap music, movies, photos, and applications,
provided they do not violate copyright protections. Online chat allows people to carry on discussions using written text. Instant messaging enables people to exchange
text messages; share digital photo, video, and audio files; and play games in real time. Scientists and scholars use the Internet to communicate with colleagues,
perform research, distribute lecture notes and course materials to students, and publish papers and articles. Individuals use the Internet for communication,
entertainment, finding information, and buying and selling goods and services.

A Internet Access
The term Internet access refers to the communication between a residence or a business and an ISP that connects to the Internet. Access falls into three broad
categories: dedicated, dial-up, and wireless. With dedicated access, a subscriber's computer remains directly connected to the Internet at all times through a
permanent, physical connection. Most large businesses have high-capacity dedicated connections; small businesses or individuals that desire dedicated access choose
technologies such as digital subscriber line (DSL) or cable modems, which both use existing wiring to lower cost. A DSL sends data across the same wires that telephone
service uses, and cable modems use the same wiring that cable television uses. In each case, the electronic devices that are used to send data over the wires employ
separate frequencies or channels that do not interfere with other signals on the wires. Thus, a DSL Internet connection can send data over a pair of wires at the same
time the wires are being used for a telephone call, and cable modems can send data over a cable at the same time the cable is being used to receive television signals.
Another, less-popular option is satellite Internet access, in which a computer grabs an Internet signal from orbiting satellites via an outdoor satellite dish. The user

usually pays a fixed monthly fee for a dedicated connection. In exchange, the company providing the connection agrees to relay data between the user's computer and
the Internet.
Dial-up is the least expensive access technology, but it is also the least convenient. To...

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