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The WWW is a new way of viewing information -- and a rather different one. If, for example, you are viewing this paper as a WWW document, you will view it with a browser, in which case you can immediately access hypertext links. If you are reading this on paper, you will see the links indicated in parentheses and in a different font. Keep in mind that the WWW is constantly evolving. We have tried to pick stable links, but sites reorganize and sometimes they even move. By the time you read the printed version of this paper, some WWW links may have changed.

The World Wide Web

The WWW project has the potential to do for the Internet what Graphical User Interfaces (GUIs) have done for personal computers -- make the Net useful to end users. The Internet contains vast resources in many fields of study (not just in computer and technical information). In the past, finding and using these resources has been difficult. The Web provides consistency: Servers provide information in a consistent way and clients show information in a consistent way. To add a further thread of consistency, many users view the Web through graphical browsers which are like other windows (Microsoft Windows, Macintosh windows, or X-Windows) applications that they use. A principal feature of the Web is its links between one document and another. These links, described in the section on hypertext, allow you to move from one document to another. Hypertext links can point to any server connected to the Internet and to any type of file. These links are what transform the Internet into a web.

A History of the Web

The Web project was started by Tim Berners-Lee at the European Particle Physics Laboratory (CERN) in Geneva, Switzerland. Tim wanted to find a way for scientists doing projects at CERN to collaborate with each other on-line. He thought of hypertext as one possible method for this collaboration. Tim started the WWW project at CERN in March 1989. In January 1992, the first versions of WWW software, known as Hypertext Transfer Protocol (HTTP), appeared on the Internet. By October 1993, 500 known HTTP servers were active. When Robelle joined the Internet in June 1994, we were about the 80,000th registered HTTP server. By the end of 1994, it was estimated that there were over 500,000 HTTP servers. Attempts to keep track of the number of HTTP servers on the Internet have not been successful. Programs that try to automatically count HTTP servers never stop -- new servers are being added constantly.

On-Line versus Batch

This paper is available on the World Wide Web (on-line) or as a paper document (batch). If you are reading this via Robelle's WWW Service, you probably already know how to access the on-line version. Much of the value of the Web lies in its links between one document and another. When you view this paper with a WWW browser, the links are hidden from you. When you read the text or paper copy of this paper, you see the links in parentheses. Because links tend to be long, they do not format well in the text and paper versions. Since more than half the effort of writing this paper went into finding and testing the links, we have left them in the text and printed versions, despite their distracting appearance. We will describe what the links mean a little later.

What is Hypertext?

Hypertext provides the links between different documents and different document types. If you have used Microsoft Windows WinHelp system or the Macintosh hypercard application, you likely know how to use hypertext. In a hypertext document, links from one place in the document to another are included with the text. By selecting a link, you are able to jump immediately to another part of the document or even to a different document. In the WWW, links can go not only from one document to another, but from one computer to another.

Client/Server Computing

The last few years have seen an explosion of information about client/server computing. For many people, the definition of client/server is still unclear. We describe it as a method of distributing applications over one or more computers. A client is one process that requests services of another process. These processes can be on different computers or on the same computer. The processes communicate via a networking protocol.

People often think of client/server computing in terms of local area networks, PCs with graphical user interface capabilities, and servers with information that is needed by the PC clients. You do not have to implement client/server computing this way. It is possible for the same computer to be both the client and the server. The key point is that there is a communications protocol that allows two processes (often on different computers) to request and to respond to demands for services.

The Hypertext Transfer Protocol

When you use a WWW client, it communicates with a WWW server using the Hypertext Transfer Protocol (HTTP). When you select a WWW link, the following things happen:

  1. The client looks up the hostname and makes a connection with the WWW server.
  2. The HTTP software on the server responds to the client's request.
  3. The client and the server close the connection.
Compare this with traditional terminal/host computing. Users usually logon (connect) to the server and remain connected until they logoff (disconnect). An HTTP connection, on the other hand, is made only for as long as it takes for the server to respond to a request. Once the request is completed, the client and the server are no longer in communication.

WWW clients use the same technique for other protocols. For example, if you request a directory at an anonymous FTP site, the WWW client makes an FTP connection, logs on as an anonymous user, switches to the directory, requests the directory contents, and then logs off the FTP server. If you then select a file, the WWW client once again makes an FTP connection, logs on again, changes directories, downloads the file, and then logs off. If you use an FTP client to do the same thing, you would normally log on to the FTP server, change directories several times, and download one or more files. Only when you were finished would you log off.

The Internet

The Internet is the world's largest interconnected computer network. Computers on the Internet communicate using the Internet Protocol (IP) and the Transmission Control Protocol (TCP). You identify individual computers by their IP-address. This address is a 32-bit number that is usually represented by four octets (e.g., Fortunately, you can usually refer to a computer by its name (e.g.,

If you can send network packets to one computer on the Internet, you can send network packets to any computer on the Internet. This feature is what makes the Internet so powerful; it is also what concerns system managers. If you can send packets to the Internet, it follows that anyone can send packets to your computer, even the PC on your desktop.

Accessing the Internet

If you are reading the text or paper version of this paper, you're probably wondering "How do I get started on the Internet?" It is much easier to connect an individual PC and a modem to the Internet than it is to connect a server like an HP 3000 or HP 9000. We suggest that you find a local Internet access provider to connect your PC to the Net. Most access providers include everything you need to log on and start exploring. In addition, several books on connecting to the Internet also provide all the software and the telephone numbers of Internet access providers you need to get started. Once you're connected to the Internet, you can begin investigating many of the sites described in this paper. You will also be able to access and download much of the software needed to create your own WWW application which, as we discuss further on, can be of help to you, even if you never plan to connect your servers to the Internet.