Computer Network Definition

A computer network, also referred to as just a network, consists of two or more computers, and typically other devices as well (such as printers, external hard drives, modems and routers), that are linked together so that they can communicate with each other and thereby exchange commands and share data, hardware and other resources.

The devices on a network are referred to as nodes. They are analogous to the knots in nets that have traditionally been used by fishermen and others. Nodes can be connected using any of various types of media, including twisted pair copper wire cable, optical fiber cable, coaxial cable and radio waves. And they can be arranged according to several basic topologies (i.e., layouts), including bus (in which all nodes are connected along a single cable), star (all nodes are connected to a central node), tree (nodes successively branch off from other nodes) and ring.

The smallest and simplest networks are local area networks (LANs), which extend over only a small area, typically within a single building or a part thereof. A home network is a type of LAN that is contained within a user's residence. Wide area networks (WANs) can extend over a large geographic area and are connected via the telephone network or radio waves. A metropolitan area network (MAN) is designed to serve a town or city, and a campus area network is designed to serve a university or other educational institution.

An intranet is a private network within an organization that uses the same communications protocols as the Internet. When part of an intranet is made accessible to suppliers, customers or others outside the organization, that part becomes an extranet.

An internet (spelled with a lower case i) is a network that is composed of a number of smaller computer networks. The Internet (spelled with an upper case I) is the world-wide network of interconnected internets that operates using a standardized set of communications protocols called TCP/IP (transmission control protocol/Internet protocol), or the Internet protocol suite. This ultimate internet is vastly larger than any other internet and connects thousands of networks and hundreds of millions of computers throughout the world.

A protocol defines a common set of rules and signals that computers on the network use to communicate. TCP/IP is not only the protocol of the Internet, but it has also become the dominant protocol for computer networks of virtually all types. Originally developed for use in UNIX, TCP/IP is now built into virtually all major computer operating systems. Reasons for its success, and thus for the astonishing success of computer networks in general, include the facts that it is intelligent, robust, compatible with nearly all types of hardware and operating systems, relatively simple and free software (which means that it free with regard to both cost and use).

An important feature of modern computer networks, at least when Linux and other Unix-like operating systems are used, is network transparency. This means that a users can access resources (e.g., application programs or data) without needing to know, and usually not being aware of, whether the resources are located on the local machine (i.e., the computer which the user is currently using) or on a remote machine (i.e., a computer elsewhere on the network). Network transparency can be a major convenience to users, as it relieves them from having to be concerned about the details of the structure of the network and of having to take special steps to access remote data. It can also help simplify the tasks of program developers and system administrators.

Computers were originally stand-alone systems that consisted of a mainframe that was connected to a number of input and output devices (mainly keyboards, punched card reading/punching machines and printers). The ability for multiple computers to be connected over long distances began in 1969 at the University of California at Los Angeles (UCLA) with the development of ARPANET, which was established by the U.S. Defense Advanced Research Project Agency. This ability has made computers vastly more powerful and useful, because it has, in effect, made the network into a computer1.

Networks have existed as long as there have been communications. Indeed, networking is an inherent part in any natural system, whether it be a single organism (in which the cells and other body parts communicate via electrical and chemical signals), an ecosystem (in which the various organisms communicate through sensing organs, chemicals and other means) or even a planetary system (in which the various bodies are connected through gravity, solar radiation, etc.)

The first long distance human communication networks were formed using runners2, smoke signals, drum beats and semaphores. The first type of electrical network was the telegraph, which began operation around 1833 in the UK. Telephone networks began replacing the already extensive telegraph networks soon after Alexander Graham Bell received his patents for the telephone in 1876. Computer networks started out by operating over telephone networks that were designed primarily to carry voice traffic. But now computer networks are rapidly moving to replace telephone networks as the dominant type of network, and voice traffic, in the form of VoIP (voice over Internet protocol), is just one of many types of traffic carried by such networks.

Computer network technology continues to advance, and this is resulting in the availability of new and improved hardware and services along with greater ease of use and lower cost. Among the many areas of development are ad hoc networks, which can be created instantly as needed and can then dismantled just as quickly, and networks of things, which can include virtually any item in a network through the use of technologies such as RFID (radio frequency identification) tags and IPv6 (Internet protocol version 6) addressing. However, it is important to keep in mind that along with all of these advances come new dangers, as is typically the case with technological advance.

1This was expressed very well by John Gage, chief researcher at Sun Microsystems, in 1984 with his now famous quotation "The network is the computer."

2For example, the ancient Incas constructed an elaborate system of stone roads and rope suspension bridges roads for use by trained runners who carried official messages throughout the empire which centered on what is today Peru. The roads had a total length of roughly 10,000 miles and messages could, on average, be transported well in excess of a hundred miles per day.

Created September 12, 2005. Last updated September 3, 2006.
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