The Internet is not just one large computer network; it is an internation-al network of computer networks. These networks are of different shapes and sizes and are scattered all across the world. The network that was the foundation of the Internet dates back to the 1950s. The U.S. government created an agency within the Department of Defense called ARPA (Advanced Research Projects Agency). ARPA’s job was to make the U.S. the world leader in science and technology. In 1962, the government commissioned a study to determine how the military could maintain command and control over its missiles after an attack occurred. ARPA was given the task of designing a computer network for the military, later to be called ARPANET. In 1981, another nation-wide network, NSFNET, was built for those colleges that did not have access to ARPANET. By the early 1990s, most networks were leaving the slower ARPANET and linking to NSFNET, which was then called the Internet.
One of the key elements of how the Internet works is the Do-main Name System (DNS). The role of the DNS is to look up a Web site’s IP number when given its name. The DNS is a data-base, organized as a hierarchy (or tree), of the name of each site on the Internet and its corresponding IP number. Instead of being on only one computer, the DNS database is divided and distributed to many different servers on the Internet, each being responsible for different areas of the Internet.
A number of different tools are used for accessing information on the Internet. A Web browser lets a user view text, data, pic-tures, animation, and video on the Internet by using a graphical user interface. Prior to Web browsers, users were forced to memorize and type in long character-based commands. The most common tool used on the Internet is e-mail. A variety of e-mail packages are available. Modern e-mail packages have a graphical user interface and are accessible through a Web browser. Documents sent along with e-mail messages are known as attachments. Many users turn to file compression software, which reduces the size of an attachment by compress-ing the file. This software looks for patterns of characters in the file and substitutes a single symbol for a string of characters.
A listserv is an automated way to send e-mail to a group. Users subscribe and unsubscribe to a listserv list. When an e-mail message is sent to the list, the listserv program automatically copies the incoming message and sends it to the e-mail address of each person in the group. The listserv program takes care of all of these tasks so users do not have to create and maintain distribution lists. A newsgroup allows users to post questions and answers in a central location instead of sending them direct-ly to each member. One of the advantages of a newsgroup is that all messages are stored in one central location, meaning that the user does not have to save individual e-mail messages. Also, a newsgroup makes it easy to follow a discussion thread.
There are two basic types of search tools. The first is searching an online service, or portal. Portals provide ready-made menu lists of information from which users can select. These lists may include sports, education, food, health, and a wide range of other topics. Another type of search tool is a search engine which automatically searches the Internet and compiles a data-base that can be searched quickly by a user.
Hypertext Markup Language (HTML) is the underlying founda-tion of all Web pages. HTML is a standard way of defining how text, pictures, and graphics should appear on a Web page. HTML is interpreted by a Web browser, which displays the con-tent based on the instructions, or tags, contained in the HTML document. An HTML Web page is made up of elements, and these are defined by the use of tags.