Let's say I have a box containing all the knowledge in the world. How much would you pay me for it? Oh, one more thing. It's a sealed box and nothing you can do will open it. Nothing, not now or ever. It has no hinges or even a lid. You can't saw the top off or even bore a hole through one of the sides. It resists all acids, nuclear explosions, even Superman's X-ray eyes. It is just an unopenable, sealed box that I absolutely guarantee you is filled with the answers to all your questions and all those of everyone else in the world. And it's a nifty box, oak-oiled a nice, rich brown.
I'd guess you might offer a few dollars, whatever its decorative value. You might even eye it for seating if you didn't have a chair (though I have to admit that the box is not all that big—and it sounds pretty empty at that). Basically, the value of all that knowledge is nothing if you can't get at it and use it.
What would your computer be worth to you if you couldn't get your answers out? If you couldn't connect with the Internet? If you couldn't plug in a CD writer or even a printer? I'd wager not much. It's even an uncomfortable flop as a chair.
Fortunately, your computer is not resistant to a handsaw or electric drill. You can even open it up with a screwdriver. Better still, you can simply plug in a cable or two and connect up with another computer, a network, the Internet, or an Erector set. Your computer is a superlative communications machine. That's what gives it its value—unless you really are using yours as a chair.
A computer communicates in many ways, both outside and inside its box. Moving information around electronically takes a lot of ingenuity and some pretty amazing technologies. Your system's microprocessor must organize its thoughts, make them into messages that it can send out through its ports or down the wires that make up its expansion bus. It needs to know how to talk and, more importantly, how to listen. It needs to put the signals in a form that other computers and add-on devices (peripherals) can understand—a form that can travel a few inches across a circuit board, tens of thousands of miles through thin copper wires, or as blips of light in a fiber-optic cable. And it has to do all that without making a mistake.
The next seven chapters outline how your computer communicates. We'll start out with the concepts that underlie all computer (and, for that matter, electronic) communications. From there, we'll step into the real world and examine how your system talks to itself, sending messages inside its own case to other devices you might install there. We'll look at the interfaces it uses to send messages—the computer's equivalent of a telephone handset that it speaks and listens through. Then we'll examine how it connects to external devices, all the accessories and peripherals you plug in. From there, we'll examine the technologies that allow you to connect to the most important peripherals of all—other computers—both in your home or office on a network, and elsewhere in the world through the Internet.
There's a lot to explore, so you might as well put your feet up. After all, a computer may not work well as a chair, but it can be a pretty good footstool.