Text 12. Hypertext

Hypertext is also called Hyperlinking, the linking of related pieces of information by electronic connections in order to allow a user easy access between them. Hypertext is a feature of some computer programs that allow the user of electronic media to select a word from text and receive additional information pertaining to that word, such as a definition or related references within the text. In the article "whale" in an electronic encyclopedia, for example, a hypertext link at the mention of the blue whale enables the reader to access the article on that species merely by "clicking" on the words "blue whale" with a mouse. The hypertext link is usually denoted by highlighting the relevant word or phrase in text with a different font or colour. Hypertext links can also connect text with pictures, sounds, or animated sequences.

Hypertext links between different parts of a document or between different documents create a branching or network structure that can accommodate direct, unmediated jumps to pieces of related information. The treelike structure of hyperlinked information contrasts with the linear structure of a print encyclopaedia or dictionary, for example, whose contents can be physically accessed only by means of a static, linear sequence of entries in alphabetical order. Hypertext links are, in a sense, text cross-references that afford instant access to their target pieces of information. Such links are most effective when used on a large array of information that is organized into many smaller, related pieces and when the user requires only a small portion of information at any one time. Hypertext has been used most successfully by the interactive multimedia computer systems that came into commercial use in the early 1990s.

Text 13. Computer network

Computer network is also called Network, two or more computers that are connected with one another for the purpose of communicating data electronically. Besides physically connecting computer and communication devices, a network system serves the important function of establishing a cohesive architecture that allows a variety of equipment types to transfer information in a near-seamless fashion. Two popular architectures are ISO Open Systems Interconnection (OSI) and IBM's Systems Network Architecture (SNA).

Two basic network types are local-area networks (LANs) and wide-area (or long-haul) networks. LANs connect computers and peripheral devices in a limited physical area, such as a business office, laboratory, or college campus, by means of permanent links (wires, cables, fibre optics) that transmit data rapidly. A typical LAN consists of two or more personal computers, printers, and high-capacity disk-storage devices called file servers, which enable each computer on the network to access a common set of files. LAN operating system software, which interprets input and instructs networked devices, allows users to communicate with each other; share the printers and storage equipment; and simultaneously access centrally located processors, data, or programs (instruction sets). LAN users may also access other LANs or tap into wide area networks. LANs with similar architectures are linked by "bridges," which act as transfer points. LANs with different architectures are 1inked by "gateways," which convert data as it passes between systems.

Wide-area networks connect computers and smaller networks to larger networks over greater geographic areas, including different continents. They may link the computers by means of cables, optical fibres, or satellites, but their users commonly access the networks via a modem (a device that allows computers to communicate over telephone lines). The largest wide-area network is the Internet, a collection of networks and gateways linking millions of computer users on every continent.