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Chapter 2. Functions and Components

Going through a long-winded description of what a computer is doesn't seem to make sense when you can see what a computer is, sitting right in front of you. It's a box, a keyboard, and a screen with a headache attached.

Rather than looking at a strictly formal definition of a computer, it's probably more useful to learn what it is with a more practical approach: Examine the machine in front of you. After all, you can see the parts and how they fit together.

If you have a desktop computer or a tower, you've got a big box with an empty slot or two on the front and a bunch of jacks and connectors on the back. A notebook scatters the slots and jacks all around its edges, but in either style of case you get essentially the same repertory. And, if you look closely in either case, you'll see that all the parts are held together with a few screws. With a flashlight in hand, you might be able to squint through the slots and see some of the internal parts. Get daring and twist out the screws, and you'll get a much better view. But there will still be something you cannot see—what those parts do.

The functions of the components of a computer are not at all obvious based on what they look like. Although some machines make the functions of their parts quite obvious—the wheels of a car pretty much shout their function—with a computer, the function of each part is hidden in a snarled mass of digital electronic circuitry and accompanying programs. Take, for example, arguably the most important part of any modern computer, the microprocessor. Its inner workings must be protected inside a hermetically sealed case because air would destroy the delicate crystalline circuits inside. Even if the microprocessor were encased in glass, however, you could never see the electricity flowing through it or the logic operations it performs in creating your computer's thoughts. About the only electricity you can normally see is lightning, and you probably hope you'll never see that inside your computer.

Even though all the good stuff inside a computer is essentially invisible, examining the individual parts that deal with the stuff you can't see is key to understanding how the whole thing works. This microscope-to-the-parts strategy makes sense for economic as well as explanatory reasons. You buy a computer as a collection of parts, even if you pay one price and get one big box. One reason is that not all computers are the same, a fact that should be obvious as soon as you pull out your credit card. You can buy a brand new (though technologically old) computer for barely more than $100 today, or you can pay fifty times more. Even though you might not notice a difference between them when you run Microsoft Word—scary as it sounds, that's often true for reasons you'll understand before you finish this book—manufacturers and retailers can easily justify the difference. One machine can handle some tasks (obviously other than running Word) more adroitly than the other. The underlying reason for this difference is a matter of the component parts from which the two machines are made.

Electronic devices, whether computers, digital cameras, or portable radios, are all built from tiny electronic parts such as resistors, capacitors, transistors, and integrated circuits. Each of these changes the flow of electronics in some small, simple way, and figuring out how to connect them together to accomplish some tiny task is how electrical engineers earn their salaries. But combine these tiny assemblies together at the next level (another task for engineers), and the result is a module or computer component with a definite, defined task. Each is a subassembly like the various parts of a car or refrigerator. A car has a motor, wheels, steering system, doors, and windows. A refrigerator has a motor, a compressor, cooling coils, a box, doors, and insulation. Similarly, every computer is built from an array of components, such as a microprocessor, power supply, and flashing lights.

Each of these individual components has a well-defined function. For example, in your car, the motor, transmission, axle, and wheels make the car move along the highway, providing the motive function. In the refrigerator, the motor, compressor, and coils make up the cooling function.

Of course, the car has other functions in addition to its motive function. For example, the body, windows, and seats provide a passenger-carrying function, much as a refrigerator has a food-holding function. Although at first thought such secondary functions might seem incidental to the overall concept of the car or refrigerator, these functions are actually essential parts that help define what a car or refrigerator is. After all, you wouldn't have much of a car if it couldn't go anywhere or hold people. Nor would a refrigerator be as useful if it couldn't keep cool or hold food.

Similarly, the computer has several functions that define what it is and what it does. Although some of the functions might seem incidental to the concept of a computer as a thinking (or calculating) machine, all are essential for making a modern computer the useful device that it is.

The typical modern personal computer has four major functions. These include thinking, communicating, remembering, and listening and monitoring, all tied together by an electronic and mechanical infrastructure. Of course, this division is somewhat arbitrary. Some people might, for example, combine thinking and remembering, and others (say people who sell security software) might add additional functions, such as security. But this five-way split has one big advantage over any other: It's how I've chosen to arrange this book.

Each of these functions requires one or more hardware components to carry it out. For example, thinking is not merely a matter for microprocessors. It requires memory in which to execute programs, a chipset to link the microprocessor's circuits to the rest of the computer, and some semi-permanent software in the form of the BIOS to bring everything to life. Memory involves not only the chips that we think of as computer memory but also devices for longer-term memory, which include hard disks and other mass storage devices that keep a computer from forgetting even after you switch its power off.

We'll start our computer tour by taking a look at these functions and subdividing them into the components your computer uses to carry them out.

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