Input/Output Ports

Your computer links to its peripherals through its input and output ports. Every computer needs some way of acquiring information and putting it to work. Input/output ports are the primary routes for this information exchange.

In the past, the standard equipment of most computers was simple and almost preordained—one serial port and one parallel port, typically as part of their motherboard circuitry. Modern standards are phasing out these ports, so we'll consider them (for purposes of this book) legacy ports. Today, new and wonderful port standards are proliferating faster than dandelions in a new lawn. Hard-wired serial connections are moving to the new Universal Serial Bus (USB), whereas the Infrared Data Association (IrDA) system and oddly named Bluetooth provide wireless links. Digital video connections use FireWire, also called IEEE 1394. Even the simple parallel port has become an external expansion bus capable of linking dozens of devices to a single jack.

The ports are the jacks or connectors you'll find on the back of most desktop computers or scattered around the edges of notebook machines. They come in various sizes and shapes, meant to match special connectors unambiguously.

Expansion Buses

Computers need to communicate with any of a number of peripherals, some of which reside inside the computer's case. The primary link to these internal components is the expansion bus.

As the name implies, the expansion bus of a computer allows you to expand its capabilities by sliding in accessory boards (cleverly termed expansion boards). For this to work, the expansion bus sets up an internal communication channel inside your computer. Expansion slots are spaces inside the computer that provide special sockets or connectors to plug in the capabilities and functions locked in the circuitry of the expansion boards.

In a desktop computer, the expansion bus usually is a row of three or more long connectors on the main circuit board near the back of the computer's case. Depending on the overall design of the computer, one or more of these slots will be filled with expansion boards in the basic factory configuration. In a notebook computer, expansion slots are different, meant to accept modules the size of credit cards that deliver the same functions as expansion boards.

BIOS

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.

Chipset

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.

Microprocessor

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.