The World Wide Web operates using a client/server networking principle. When you enter the URL (the web address) of a web page into your browser and click on “Go,” you ask the browser to make an HTTP request of the particular computer having that address. On receiving this request, that computer returns (“serves”) the required page to you in a form that your browser can interpret and display. Figure 1.1 illustrates this relationship. In the case of the Internet, of course, the server and client computers may be located anywhere in the world.

Later we’ll discuss the nitty-gritty of HTTP requests in more detail. For now, suffice it to say that your HTTP request contains several pieces of information needed so that your page may be correctly identified and served to you, including the following:

• The domain at which the page is stored (for example, mydomain.com)
• The name of the page (This is the name of a file in the web server’s file system—for example, mypage.html.)
• The names and values of any parameters that you want to send with your request