The Internet is a vast network of computers that connects many of the world's businesses, institutions, and individuals. The Internet, which is short for interconnected network of networks, links tens of thousands of smaller computer networks. It enables users of computers and other networked devices throughout the world to send and receive messages, share information in a variety of forms, and even play computer games with people thousands of miles or kilometers away. Computers linked to the Internet range from simple and inexpensive personal computers, often called PC's, to huge mainframe computers used by government institutions, educational institutions, and businesses. Other devices linked to the Internet include sophisticated telephones and televisions.

Computers and other devices require special hardware and software to connect to the Internet. Necessary hardware includes a modem or an adapter. A modem is a device that translates a computer's digital (numerical) information into signals that can be transmitted over telephone lines, over cable, or through the air as wireless communications (see Modem). An adapter, also called a network interface card, links a computer to a high-speed communication system designed to carry data in digital form. Adapters are often called modems, though they are not true modems. Required software includes a communications program that allows the transmission and receipt of messages. Many computers and computing devices come with modems and communications software installed.

The Internet, often called simply the Net, began as a collection of text-only documents intended for scientists, universities, and some parts of government. But the development and rapid growth of the World Wide Web (also known as the Web) transformed the presentation of information on the Net. The Web is a worldwide system of interconnected computer files linked to one another on the Net. It enables the use of multimedia—which includes photographs, moving pictures, and sound as well as text. Multimedia presentations on the Web approach the visual quality of television and the audio (sound) quality of recorded music.

The Web consists of millions of Web sites, collections of information at specific electronic addresses. Web sites in turn contain Web pages that hold multimedia or text-only information. Web sites and their pages reside in computers connected to the Internet.

Uses of the Internet

Today, tens of millions of people and businesses use the Net and the Web daily. The major uses include communications, research, publishing, business transactions, and push technology, which employs the Web for the broadcast of video and audio programming.

Communication. Probably the most popular use of the Internet and the Web is sending and receiving e-mail (electronic mail). The number of e-mail messages sent each year far exceeds the number of pieces of traditional mail carried by the world's postal systems.

Individuals, companies, and institutions have e-mail addresses that enable the sending and receipt of mail, just as a street address or post office box provides directions for traditional mail delivery. Users generally acquire e-mail addresses through an Internet service provider (ISP) or an online service. Both of these types of businesses provide access to the Internet. An ISP maintains its customers' e-mail addresses, routes e-mail and requests for Internet-based information to and from its users, and manages high-speed communications lines that quicken the transfer of data over the Internet. An online service resembles an ISP, but it provides a wide range of exclusive content in addition to Internet access. Most ISP's and online services allow customers to have several different e-mail addresses.

Many e-mail users attach illustrations, sound files, and even videos to their e-mails. An e-mail recipient whose computer system contains the required software can then view and listen to attachments as well as read the text message. Attachments may include charts and graphs, and even the text of entire books.

The Internet easily enables multiple mailings, the sending of the same e-mail to many addresses. Businesses advertise products and services via e-mail. Newsgroups—loose organizations of people who share a common interest—also use multiple mailings. They send their members copies of e-mail on the subject of interest. Members can respond to those e-mails and may introduce new topics.

Because much e-mail contains financial and other private information, most e-mail software includes encryption technology—programs that convert private e-mail into secret code for transmission. Similar software decrypts (translates back into readable language) the code when it reaches its intended destination.

Many people communicate over the Internet using instant messaging. This technology notifies a user when a friend or co-worker from a list created by the user is online. It then enables the two to communicate through text messages that can be seen by both users as the messages are typed.

Research. Much of the Internet resembles a vast library, containing as much information on every subject as might be held in tens of millions of books. Information may appear as files consisting only of text or as multimedia displays.

Special types of programs called search engines help people sort through the vast amounts of information on the Internet. Web users can choose from many search engines available on Web pages. A search engine allows a user to enter a topic for search, then finds Web pages that match that topic.

Because of the ease with which computers store information, and the speed with which computer users can access it, the Internet serves as a popular first stop for many people investigating a particular topic. A businessperson might search Internet resources for help in developing sales or product information. Students can access databases to find material related to homework assignments. Physicians can use the Net to compare medical treatments and to review advances in medical science. Scientists can share research data on the Net.

Publishing. Publishers increasingly use the Internet as a medium for presenting the contents of newspapers, magazines, and books. Because information on the Net is electronic, the publisher saves the costs of paper, printing, and distribution. More importantly, the publisher can update information almost instantly, making it possible to distribute far more current news than could be provided on paper.

Electronic versions of newspapers and magazines often contain more information than a paper publication could include. Web-based publications can also present interactive features. For example, a news story may contain links (interactive connections) to related stories or background information. If a reader wishes to explore the linked material, he or she simply clicks on a highlighted word to connect to a Web page containing that information.

The Internet also serves as a distribution system for e-books (electronic books). An e-book consists of digital files formatted so that when a reader downloads (transfers) them to a special handheld device—or to a computer with special software—the words and pictures appear much as they would on a printed page. A customer can buy e-books at the publisher's Web site or at a site owned by a bookstore. Some electronic library sites include text-only e-books. These e-books can be viewed without the use of special devices or software.

Business transactions. Many companies use the Internet to carry out business transactions commonly referred to as e-commerce. Retailers sell nearly every type of product over the Internet. Users generally pay for such purchases with credit cards. Software publishers view the Net as a convenient and inexpensive way to distribute their products. Over the Internet, users can buy new computer programs, sample programs before purchasing them, or receive upgrades to programs they already own. Music publishers sell copies of songs as downloadable digital files.

Transactions between companies and consumers are commonly known as B2C (business to consumer) transactions. Additionally, many companies use the Internet to engage in B2B (business to business) transactions. By linking together in a vast network, buyers and sellers can share information, keep track of inventories, assess needs, and compare products far more efficiently than they could using traditional business communications.

The Internet has important uses within the financial community. Many banks and stockbrokers offer their customers software to make and track investments from their computer. Consumers can use similar software to pay many types of bills. Individuals can also file tax returns and pay taxes over the Internet. Economic transactions over the Internet use encryption technology to protect the privacy and security of the users.

A popular type of Internet business is the online auction. Online auctions enable people to post descriptions of items they wish to sell, along with a suggested opening bid. Visitors to the auction site may place a bid on any posted item. Consumer auction sites offer almost every imaginable type of item. But most forbid the sale of dangerous or illegal materials. Business auction sites, also called trading exchanges, have captured a large share of B2B transactions. Such sites may, for example, offer manufacturers the chance to bid on raw materials.

Push technology, also known as Webcasting or Netcasting, takes advantage of the ability of the Internet and the Web to deliver high-quality digital audio or video signals. Push technology enables producers to distribute their presentations to PC's and other devices capable of receiving and playing them.

Push technology programs have no fixed schedules. A producer can offer audio or video presentations to anyone who subscribes to them. The user might either download the entire video to his or her computer for later playback or play it in real time over the Internet. Real-time play is possible through a technology called streaming. Many radio stations stream their programming in real time so that people throughout the world may listen over the Web. Many also offer downloads of previous programming.

Television networks and movie producers often use push technology to promote their products and to present clips from programs and motion pictures. Some television producers have created programming specifically for the Web. Such programs are often called Webisodes.

Some television news organizations use the Web to post additional stories, constantly updating the news. They also offer extended versions of interviews and other features. Popular offerings include weather reports, global financial information, sports scores, and breaking news.

The Net is a popular showcase for short independent films. Many independent and amateur filmmakers create films using digital video cameras, which store video in digital format suitable for transmission over the Internet. They can then use special software to edit their films and to add professional-quality special effects.

Other uses. Yet another popular feature of the Net is chat. Using special software, users can gather in electronic "chat rooms" and send typed messages back and forth, discussing topics of common interest. The Internet also features many Web-based games with animation, sound effects, and music. Game players can challenge others in distant countries to tournaments.

The creation of personal Web pages is a particularly popular use of the Web. Individuals create and maintain these pages. Some people use such pages to share personal information or to promote particular ideas and theories. One type of page, called a Weblog or blog, is a personal journal of thoughts and ideas for other users to read. A Weblog may also contain links to an individual's favorite Web sites. Most ISP's and online services provide space on a resource computer called a server, or host, for hosting (storing) Web pages for individuals. Many services include the use of this space in the subscription price. But some charge the individual separately for the use of server space.

Advertisers often place messages on frequently visited Web pages. Links join these messages electronically to the advertiser's own Web site. In effect, advertisers can invite Internet users to view commercials on their computer. Additionally, a user can supply the advertiser with his or her e-mail address to get further information, or such incentives as discount coupons.

How the Internet works

Computer networks enable computers to communicate and share information and resources. The simplest networks consist of a user's computer, known as the client, and a server. The client makes requests of the server, which, in turn, provides the requested resources, such as information or software. The Internet works in much the same way, on a far vaster scale. To connect to the Net, a user logs on by instructing his or her computer's communications software to contact the ISP or online service. To protect the user's security, this process usually requires a secret password.

The Internet was built around telephone connections that were, for the most part, the same as those used for voice communications. But the ever-increasing volume of Internet traffic, and the large size of video and sound files, require faster communications links. High-speed links, often called broadband connections, can deliver large amounts of information more quickly than traditional telephone lines can.

Among the most common broadband connections are (1) cable television connections, (2) fiber-optic telephone lines, (3) ISDN (integrated services digital network) and DSL (digital subscriber line), and (4) satellite connections. Cable television connections use the same cables that deliver television signals to carry Internet traffic. They require the use of a special cable modem. Fiber-optic telephone lines employ thin, high-capacity fibers to transmit vast amounts of information as patterns of light. ISDN and DSL use new technologies to increase the information-carrying capacity of traditional copper phone lines. Satellite connections use wireless communications with orbiting satellites. They enable people to use the Internet even in locations with no land-based communications lines.

Once connected to the ISP or online service, the user has several options. The user's communications software alone may provide access to such functions as e-mail and newsgroups. Most such software also includes a simple word processing program that enables a user to compose, revise, or read messages. A piece of software known as a browser enables a user to gain access to millions of Web sites. Each site has a separate electronic address, known as a uniform resource locator (URL). Many search engines and other programs throughout the Internet maintain and constantly update directories of addresses.

The addresses themselves are organized into various top level domains (major categories). In a URL, the top level domain takes the form of a of an extension of two or more letters, such as .ca for Canada, .com for commercial, .edu for educational, or .museum for museum. An organization called The Internet Corporation for Assigned Names and Numbers (ICANN) coordinates the assignment of top level domains. In the United States, a domain name includes a top level domain and a second level domain. In the domain name worldbook.com, for example, worldbook is the second level domain.

By typing an address, or by clicking on a link, a user transmits a request through the ISP or online service and onto the larger Internet. When the request arrives at the desired destination, the server responds by sending the user the requested information. This information is often in the form of a starting page called a home page, which often resembles the table of contents of a book or magazine. From a home page, the user can search for further information by using links to other pages within the same Web site or to other Web sites.

Most browsers include systems for bookmarking (recording) the addresses of favorite or frequently visited sites. A user who has bookmarked a site simply clicks on the appropriate bookmark to visit the site again.

Many individuals maintain personal Web sites under domain names that include their own names. Several companies register domain names. Many ISP's and online services also register domain names for their customers for an added charge.

Many files, especially illustration, motion-picture, and sound files, travel over the Internet in compressed form. One compression technique stores data that represent a less precise version of an image or sound than the original file does. Another technique saves space by removing image or sound data that are repeated, then merging all the repeated sections together into a separate file. When the original file is decompressed, the repeated sections return to their proper places.

Concerns about uses of the Internet

The Internet and the Web have revealed only a fraction of their potential as tools for education, research, communications, news, and entertainment. Most people believe that the benefits of the Internet far outweigh its challenges. However, some people have serious concerns over the use of the Internet.

Concerns about material. Among concerns over use of the Internet are doubts about the accuracy and appropriateness of information. Much information posted on the Internet may be misleading, inaccurate, or even fraudulent. Many teachers teach their students how to evaluate the information they find on the Internet and identify which Web sites are reputable sources.

Many parents worry about violent or pornographic material available on the Net. Criminals may lurk in chat rooms, seeking to arrange face-to-face meetings with unsuspecting victims. Special programs known as parental control software, also called Internet filters, can help parents restrict access to sites that may be unsuitable for children.

In the United States, the Children's Internet Protection Act requires the installation of such filters in public schools and libraries that provide Internet access and receive federal funding. Schools and libraries that fail to comply with the act could lose federal aid.

Security is an important concern for those who use the Internet. Mischievous programmers known as hackers often try to break into large computer systems. Some damage databases stored in these systems or attempt to steal information or electronic funds. Others may seek access to personal financial information. Many people feel concerned about the security and confidentiality of credit card numbers used to make purchases over the Internet. To protect themselves and their services from unwanted intruders, many ISP's and online services, corporations, and even individuals erect software and hardware barriers called firewalls. Such barriers seal off a server or other computer from intrusion.

Software itself can become a danger on the Internet. Programs known as viruses, e-mail bombs, Trojan horses, and worms have spread across the Internet and can cause damage to data on systems that receive them. Some of these programs have spread to computers around the world in a matter of hours. Many companies produce software designed to protect users from viruses and other such destructive programs. Most publishers of virus protection software update their programs when new types of viruses are detected. Customers can often download these updates over the Internet.

Legal issues. The distribution of e-books, digital music, and digital video poses important legal questions, particularly because digital files can be so easily pirated—that is, copied and distributed without permission or payment. Web users can e-mail copies of e-books and digital recordings anywhere. Unauthorized Web sites offer pirated e-books, recordings, or videos. Some Internet companies provide sites where people can freely share digital copies of music. At first, this sharing was free, and the traditional music industry claimed that the practice was illegal. Several music distributors participated in lawsuits against the companies. As a result, these companies have begun to charge customers for downloads and pay fees to music publishers.

Internet availability. As the Internet and Web have become more popular and powerful, concern has grown about equality of access to their resources. Computers are costly, as are ISP and online service subscriptions. To ensure more equal access to the Net, many public libraries and schools provide Internet-capable computers for individual use. In many cities around the world, establishments known as Internet cafes offer people the use of Internet-ready computers for a fee based on time of use. Such establishments are especially popular in areas of the world where many people do not have computers or even telephones.

History of the Internet

Early development. The Internet began to take shape in the late 1960's. The United States Department of Defense was concerned at the time about the possibility of devastating nuclear warfare. It began investigating means of linking computer installations together so that their ability to communicate might withstand a war. Through its Advanced Research Projects Agency (ARPA), the Defense Department initiated ARPANet, a network of university and military computers.

The network's operating protocols (rules) laid the groundwork for relatively fast and error-free computer-to-computer communications. Other networks adopted these protocols, which in turn evolved as new computer and communications technologies became available.

Throughout the 1970's, ARPANet grew at a slow but steady pace. Computers in other countries began to join the network. Other networks came into existence as well. These included Unix to Unix Copy (UUCP), which was established to serve users of the UNIX operating system, and USENET (user network), a medium for posting text-based articles on a variety of subjects.

By 1981, just over 200 computers were connected to ARPANet. The U.S. military then divided the network into two organizations—ARPANet and a purely military network. During the 1980's, ARPANet was absorbed by NSFNET, a more advanced network developed by the National Science Foundation, an independent agency of the federal government. Soon, the collection of networks became known simply as the Internet.

One of the reasons for the slow growth of the early Internet was the difficulty of using the network. To access its information, users had to master complex series of programming commands that required either memorization or frequent reference to special manuals.

The World Wide Web. The Internet's breakthrough to mass popularity occurred in 1991 with the arrival of the World Wide Web. The Web was developed by Tim Berners-Lee, a British computer scientist at the European Organization for Nuclear Research (CERN). One feature that helped popularize the Web was its ability to deliver multimedia.

The programming language that the Web used, called hypertext markup language (HTML), made it far easier to link information from computers throughout the world. This development effectively created an interactive index that enabled users to jump easily from the resources of one computer to another, effortlessly following an information trail around the world. The arrival of browsers in 1993 further simplified use of the Web and the Internet, and brought about staggering growth in the Internet.

In the 1990's, many businesses were created on the Internet. Some were considered among the most valuable businesses in the world. But their values often rested in their potential, or the excitement people felt about this new way of doing business, and few actually made a profit. By 2000, many of these companies had gone out of business. Companies that operated traditional retail businesses in addition to ones on the Internet were, on the whole, more successful.

New technologies continue to increase the importance of the Internet. Handheld computers and Internet-capable cellular telephones take advantage of satellite communications to enable people to access the Internet from any location. Wireless fidelity (also called wi-fi) and similar systems use radio waves to link a computer wirelessly to the Internet. Dedicated devices often called Internet appliances or network computers provide e-mail and Web browsing ability to people who do not require the greater capabilities of a PC. Manufacturers increasingly add computer features to television sets, and many of these sets provide Internet capabilities.

The Web has moved rapidly from inception to global acceptance. Most computer experts expect the Web to continue its rapid growth. New technologies will aid its growth by adding such features as spoken-word commands, instantaneous translation, and increased availability of historical and archival material.