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The function that defines the computer is its ability to calculate and make decisions. Without the ability to make decisions, a computer could not follow a program more complex than a simple sequence. If your computer lacked the ability to calculate, you might as well have a footstool next to your desk or a dumbbell in your briefcase. These abilities give the computer its electronic thinking power—or more importantly, help the computer enhance your own thinking power.

Several components make up the thinking function of a computer. The most important is the microprocessor, but by itself a microprocessor couldn't function. It would be like a brain without a spine and blood supply. For the computer, such support functions are handled by a chipset. In addition, the computer needs the equivalent of instinct in animals and humans, the primitive behaviors that help it survive even without learning. For the computer, the equivalent of instinct is the BIOS, a set of factory-installed, essentially unchangeable programs that give the computer its basic functions and, some say, personality.


The most important of the electronic components on the motherboard is the microprocessor. It does the actual thinking inside the computer. The power of a computer—how fast it can accomplish a given job, such as resizing a digital photo—depends on the model of microprocessor inside the computer as well as how fast that microprocessor operates (the speed is measured in the familiar megahertz or gigahertz). The kind of microprocessor also determines what software language it understands. For example, Windows computers and Macintosh computers use microprocessors from different families that understand different software languages.

As fits its role, the microprocessor usually is the largest single integrated circuit in a computer. It makes more connections, so it has the biggest socket and usually holds the dominant position on the main circuit board. It is the centerpiece of every computer. In fact, the microprocessor is the most complicated device yet devised by human beings, so complex that earlier designs couldn't fit all the silicon microcircuitry into a single chip. Many older microprocessors (such as the Pentium II series) were modules that combined several smaller integrated circuit chips into a big assembly that included a main microprocessor, a coprocessor, a cache controller, and cache memory. Today, however, everything for an advanced microprocessor such as the Pentium 4 fits on a single silicon chip about one-inch square.


The chipset of a computer provides vital support functions to its microprocessor. The chipset creates signals that are the lifeblood of the microprocessor, such as the clock or oscillator that sets the pace of its logic operations. In addition, the chipset links the microprocessor to the rest of the computer, both the memory and external functions, through input/output ports. The chipset also provides the vital link to your computer's expansion bus that enables you to add new capabilities to its repertory. The chipset is so important that in most computers it affects the performance and operation of the system as much as does its microprocessor. In fact, for some knowledgeable buyers, the choice of chipset is a major purchasing criterion that distinguishes one computer from another.

At one time, a chipset was a collection of dozens of individual electronic components. In today's computers, however, manufacturers have combined all the traditional functions of this essential support circuitry into a few large integrated circuits. In computers, in fact, the entire chipset has been squeezed into a single package. Typically the integrated circuit or circuits that make up the chipset are squares of black epoxy sitting on the main computer circuit board, usually the largest individual electronic components there, except for the microprocessor.


Just as animals rely on instincts to survive in the real world before they can learn from their experiences, a computer has a built-in program that tells it what to do before you load any software. This program is called the Basic Input/Output System because it tells the computer's microprocessor how to get input from the outside world and send output there. The BIOS defines how a computer acts and behaves before you load software. In modern computers, the BIOS has several additional functions, all essential to making the computers get started and work.

Unlike the microprocessor and chipset, the BIOS is mostly ephemeral: It is a program, a list of software codes. It takes physical form because it permanently resides in a special kind of memory chip, one that retains its memory without the need for electricity. This way, the BIOS program is always remembered, ready to be used as soon as the computer gets switched on. The chip holding the BIOS typically is a large flash memory chip. Its most distinguishing feature is its label, however. Because it holds software, the BIOS chip is usually emblazoned with a copyright notice just like other software products.

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