So far you have learned how computers connect to one another so that they can exchange information. Once the connection is established, the next stage is for data to flow between the two computers. In most situations, the computer that initiates the exchange is called the client, and the computer that receives the connection is called the server. A computer program runs on the server at all times, listening for connections from clients. On the client computer, another program (such as a web browser) connects to the server whenever it requires information. For example, when you request a Web page, the browser makes a connection to the Web server for that page when you click the Go button. In a typical client/server scenario, the client sends some data called a request to the server, and the server determines the nature of the request and formulates a response, which it sends back to the client. For example, when an email program reads your email from a mail server, the following ste...