2.1 How a Web browser works

Suppose you've just typed a URL such as http://www.intel.com/index.htm into your browser. What happens next?

First your browser has to find the IP address of www.intel.com. This is done using an Internet protocol called Domain Name Service (DNS). The details aren't important to us; it's enough to know that DNS reports Intel's Web server address to be 192.102.197.190.

Next, the browser establishes a TCP/IP session with the server at address 192.102.197.190. TCP/IP is a protocol that allows two computers on a network to send a stream of bytes to each other without worrying about network data errors. To establish a session you need both an IP address and a port number. The port number is between 1 and 65,535 (FFFF hex) which identifies the type of software that you want to talk to. In our case the port number will be 80, which is the default port for HTTP (we'll explain more about what HTTP is shortly).

Once the session is established, the browser asks the server for the data which is named by the URL. A URL is composed of three main parts: a protocol name ( http://), a server name ( www.intel.com) and a file name ( /index.htm). The browser asks for the data by sending a GET command to the server requesting the contents of that file name. The command is a text string, which could be as simple as this:

  GET /index.htm...