Internet, The - international computer network linking together thousands of individual networks at military and government agencies, educational institutions, nonprofit organizations, industrial and financial corporations of all sizes, and commercial enterprises (called gateways or service providers) that enable individuals to access the network. The most popular features of the Internet include electronic mail (e-mail), discussion groups (called newsgroups or bulletin boards, where users can post messages and look for responses on a system called Usenet), on-line conversations (called chats), adventure and role-playing games, information retrieval, and electronic commerce ( e-commerce).

The public information stored in the multitude of computer networks connected to the Internet forms a huge electronic library, but the enormous quantity of data and number of linked computer networks also make it difficult to find where the desired information resides and then to retrieve it. A number of progressively easier-to-use interfaces and tools have been developed to facilitate searching. Among these are search engines, such as Archie, Gopher, and WAIS (Wide Area Information Server), and a number of commercial indexes, which are programs that use a proprietary algorithm to search a large collection of documents for keywords and return a list of documents containing one or more of the keywords. Telnet is a program that allows users of one computer to connect with another, distant computer in a different network. The File Transfer Protocol (FTP) is used to transfer information between computers in different networks. The greatest impetus to the popularization of the Internet came with the introduction of the World Wide Web (WWW), a hypertext system that makes browsing the Internet both fast and intuitive. Most e-commerce occurs over the Web.

Each computer that is directly connected to the Internet is uniquely identified by a 32-bit binary number called its IP address. This address is usually seen as a four-part decimal number, each part equating to 8 bits of the 32-bit address in the decimal range 0–255. Because an address of the form 4.33.222.111 could be difficult to remember, a system of Internet addresses, or domain names, was developed in the 1980s. Reading from left to right, the parts of a domain name go from specific to general. For example, www.irs.ustreas.gov is a World Wide Web site at the Internal Revenue Service, which is part of the U.S. Treasury Dept., which is a government agency. The rightmost part, or top-level domain (or suffix or zone), can be a two-letter abbreviation of the country in which the computer is in operation; more than 250 abbreviations, such as "ca" for Canada and "uk" for United Kingdom, have been assigned. Although such an abbreviation exists for the United States (us), it is more common for a site in the United States to use a specialized top-level domain such as edu (educational institution), gov (government), or mil (military) or one of the four domains designated for open registration worldwide, com (commercial), int (international), net (network), or org (organization). In 2000 seven additional top-level domains (aero, biz, coop, info, museum, name, and pro) were approved for worldwide use. An Internet address is translated into an IP address by a domain-name server, a program running on an Internet-connected computer.

The Internet evolved from a secret feasibility study conceived by the U.S. Dept. of Defense in 1969 to test methods of enabling computer networks to survive military attacks, by means of the dynamic rerouting of messages. As the ARPAnet (Advanced Research Projects Agency network), it began by connecting three networks in California with one in Utah—these communicated with one another by a set of rules called the Internet Protocol (IP). By 1972, when the ARPAnet was revealed to the public, it had grown to include about 50 universities and research organizations with defense contracts, and a year later the first international connections were established with networks in England and Norway. A decade later, the Internet Protocol was enhanced with a set of communication protocols, the Transmission Control Program/Internet Protocol (TCP/IP), that supported both local and wide-area networks. Shortly thereafter, the National Science Foundation (NSF) created the NSFnet to link five supercomputer centers, and this, coupled with TCP/IP, soon supplanted the ARPAnet as the backbone of the Internet. In 1995, however, the NSF decommissioned the NSFnet, and responsibility for the Internet was assumed by the private sector. Fueled by the increasing popularity of personal computers, e-mail, and the World Wide Web (which was introduced in 1991 and saw explosive growth beginning in 1993), the Internet became a significant factor in the stock market and commerce during the second half of the decade. By 2000 it was estimated that the number of adults using the Internet exceeded 100 million in the United States alone.

See B. P. Kehoe, Zen and the Art of the Internet: A Beginner's Guide (4th ed. 1995); B. Pomeroy, ed., Beginnernet: A Beginner's Guide to the Internet and the World Wide Web (1997); L. E. Hughes, Internet E-Mail: Protocols, Standards, and Implementation (1998); J. S. Gonzalez, The 21st Century Internet (1998); D. P. Dern, Internet Business Handbook: The Insider's Internet Guide (1999).

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