The Internet A Local Area Network (LAN) typically refers to a network of computers within a limited area, usually a single building. A Wide Area Network (WAN) is a combination of two or more LANs, with a connection between them operating over some form of telecommunications link. The Internet can be viewed as the largest WAN; it not only spans the world but also has links to operations taking place in space. Many different types of networks and computers make up the Internet. These can include mainframes, UNIX and PC networks, company intranets (internal networks with Internet-type facilities), desktop PCs and notebook PCs. No restriction is placed on the type of operating system used; any computer system can connect to the Internet, either to provide information for others or to browse for information as a user. Internet computers may be located in such diverse facilities as universities, libraries and commercial organizations. The time taken to distribute information around the world has fallen from months to seconds within a period of 100 years. The Internet holds vast amounts of information, much of which is freely accessible to the public 7 days a week and 24 hours a day. It is estimated that the total amount of information held on the Internet exceeds 6 terabytes (a terabyte, TB, is approximately a million megabytes). This figure is increasing daily as more information is added. The diversity of information held on the Internet is extraordinary; some examples include: Technical computer information News and current affairs Financial and commercial information Legal decisions Arts and entertainment Sport and leisure Every piece of information on the Internet has a unique name known as a URL (Uniform Resource Locator). A URL contains all the information necessary to connect to and load a piece of information: http://www.3com.com/Ofiles/nettechs/papers/ipadd.html The Development of the Internet The Internet evolved from a US Department of Defense project in 1969 called Advanced Research Project Agency Network (ARPANET). The main objective of ARPANET was to produce a data network that would continue to operate even if parts of the network were destroyed or malfunctioning. This objective was achieved by the development of a network protocol called Transmission Control Protocol/Internet Protocol (TCP/IP). TCP/IP broke information into data packets that could be transmitted around the military network using any available path. Soon afterwards, education and government agencies such as National Science Foundation Network (NSFNet) connected to the Internet, and the Internet quickly became a playground for computer scientists and research establishments. The development of browsers and the World Wide Web in the early 1990s turned the Internet into a user-friendly environment, and it soon began to attract commercial interest. Since the mid 1990s, the Internet has become more accessible to the home computer user and is increasing in popularity all the time. Internet Services While the hardware and protocols that make up the Internet are essential, the key to its success is the information services that are available. The Internet provides a wide range of services including the World Wide Web, e-mail, newsgroups, FTP and Internet telephone. The World Wide Web The Web is one of the most popular and widespread information services on the Internet. It provides unparalleled quantities of information with a standard means of access, and user-friendly tools for locating information. The components of the web are the Web server and the browser. The server holds pages of information and makes them available to Web users, while the browser is used to locate and display information. Before the World Wide Web, information was obtained from the Internet using ASCII text or binary file transfers, both of which are very cumbersome ways of accessing information. The World Wide Web (WWW) revolutionized the distribution of information across the Internet, and also made it accessible to commercial and home users. HTML Web pages Web pages are created using a page description language named HyperText Markup Language (HTML). The text or graphics to be displayed on the Web page are inserted between a series of HTML commands (tags) that control the way the text appears. The tags do not appear on the Web page when displayed. As well as text, HTML also supports multimedia information such as graphics, pictures, sound and video. Another powerful feature is its capability to provide links to other related documents. Information saved from a browser is in HTML format and has a default file extension of .HTM. Web browsers A Web Browser is required to access Web pages. A Web browser is a software package that can retrieve and display information that has been formatted using HTML. There are many browsers to choose from, but the two most popular PC packages are Netscape Navigator and Microsoft Internet Explorer. As well as displaying Web pages, browsers have evolved to include support for additional Internet services. A user can send and receive e-mail, and participate in newsgroups through the browser. Electronic Mail (E-mail) E-mail is a messaging system that can be used to transmit text messages and file attachments such as word processing documents, graphics, video and sound. E-mail services are implemented by the SMTP protocol, which transfers messages from one server location to another, and the POP3 protocol, which allows users to retrieve messages from the server. E-mail is arguably the single most important service on the Internet, as it has become a standard means of communication for most computerized organizations. Users can send messages more or less instantaneously to anywhere in the world without incurring the cost of international telephone calls. Once the initial cost of the Internet connection has been met, the only additional cost for the use of e-mail may be local telephone calls to an Internet Service Provider (ISP). E-mail systems have been available since the early days of computing, but the facilities now available make it one of the most versatile and accessible methods of communication. There are still concerns over security on the Internet, so it is not advisable to send sensitive information by e-mail, unless it can be protected by encryption.