In late 1990 while working at CERN, the European Laboratory for Particle Physics Research in Geneva, Switzerland, Tim Berners-Lee invented the Web, including the definitions of universal resource locator (URL), hypertext transfer protocol (HTTP), and hypertext markup language (HTML). The Web provides a method for easily linking content contained on computer systems distributed throughout the world and connected to the Internet. Utilizing the Web, content on servers from many locations can be seamlessly linked and presented as a comprehensive resource collection. The Web further strengthens the power of the Internet's foundation of distributed computing.

The Web and the Internet remained the world's best-hidden resource until 1993 when Marc Andreessen, an undergraduate at the University of Illinois in Champaign, and a team at the National Center for Supercomputing Applications (NCSA) created the NCSA Mosaic browser. The NCSA Mosaic browser was the first Web-browser client that provided a friendly, point-and-click method for navigating the Internet using the Web.

The invention of the NCSA Mosaic browser was the start of the unprecedented growth of Internet users, Internet service providers (ISPs), and Internet business opportunities. By means of a user-friendly approach to searching and viewing the vast amount of information on the Internet, the Web-browser client enabled nontechnical individuals to benefit from the power and resources of the Internet.

Accessing content through the Web consists of communication between a Web-browser client and a Web server utilizing HTTP (see Figure 1).

Figure 1. Web Overview

The following is a step-by-step description of the communication path, as shown in Figure 1. It assumes that the Web server, the primary domain naming system (DNS) server, and the client computer are connected to the Internet and that all communication is conducted through the Internet.

• steps 1 and 2—The end-user types a URL into the Web browser. The client computer finds the Internet protocol (IP) number associated with the domain name in the URL from the primary DNS server.
• steps 3 and 4—The client computer uses the IP number obtained from the primary DNS server to request, through HTTP, the default HTML file from the Web server associated with the URL. The Web server sends the default HTML file to the client computer. The default HTML file provides information to the client computer for requesting all associated files—such as graphics—for the Web site's complete home page.

When the client computer and Web browser request and receive files from the same URL, the client computer is not required to perform a DNS lookup as described in steps 1 and 2. When the client computer attempts to retrieve a Web site from a different URL, the client computer must then perform steps 1 and 2 again.