We use computers without thinking about the processes going on inside them. It is easy to find out about individual components of a system, but how does the whole system work?
In order to gain an understanding of the way that computer systems work, imagine this example:
You are about to buy a DVD from Amazon. Your mouse pointer is poised over the final button on a web page, ready to confirm your order. What happens when you click the button?
We could say that your brain sends an electrical signal that causes your finger to twitch. This "click" action occurs with the left button of the mouse. But then where does that signal go? How does it end up buying you a DVD?