The real useful work that computers do involves not just you but also the outside world. Your computer must be able to communicate to put its intelligence to work. When your computer communicates with other systems far away, the process is often called telecommunications. When your computer connects with other computers over a network, engineers call the communication capability connectivity. When your computer plugs into printers and other nearby peripherals, engineers say your computer is doing what it's supposed to—there's no fancy word for it. No matter. Thanks to the communication capabilities of your computer, it can link to any of a number of hardware peripherals through its network jacks and input/output ports. Better still, through modems and the Internet, it can connect with nearly any computer in the world.

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.


Interfaces provide a communication channel that lets your computer exchange information with a variety of devices, primarily storage systems (discussed later in the chapter). The interface translates the signals inside your computer into a form that's more suited to traveling outside the confines of its main circuit boards. You've probably heard people speak about the most familiar interfaces, such as ATA (also called IDE) and SCSI, acronyms that describe connections used by hard and optical disk drives.

The interface takes the form of a connector. The ATA interface is usually built in to the main circuit board of all modern computers. A cable links this connector to one on a disk drive. The SCSI interface usually resides on a separate circuit board that fits into the expansion bus of your computer.

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.

Local Area Networks

Any time you link two or more computers together, you've created a network. Keep the machines all in one place—one home, one business, one site in today's jargon—and you have a local area network (LAN). Spread them across the country, world, or universe with telephone, cable, or satellite links and you get a wide area network (WAN). A network is both a wiring system and a software system. The wires connect computers together; the software is the language for passing messages around.

Most networks use some kind of wire to connect computers, although wireles networks are becoming popular, especially in homes where their short range is no problem and their lack of wires a great advantage.


To extend the reach of your computer beyond your home or office, you usually must rely on the international telephone system to provide the connection. Because short-sighted engineers a hundred years ago never considered that you'd want to connect your computer to your telephone, they built the phone system to use an entirely different kind of signal than your computer uses. Consequently, when you want to connect with other computers and information sources such as the Internet through the international telephone system, you need a modem to adapt your computer's data to a form compatible with the telephone system's.

In a quest for faster transfers than the ancient technology of the classic telephone circuit can provide, however, data communications are shifting to newer systems, including digital telephone services (such as DSL), high-speed cable connections, and direct digital links with satellites. Each of these requires its own variety of connecting device—not strictly speaking a "modem" but called that for consistency's sake. Which you need depends on the speed you want and the connections available to you.


The Internet is properly described as a "network of networks." In concept, it links all the computers in the world together so that they can share information (but more often games and pornography). The World Wide Web is essentially the commercial side of the Internet. Once you link up with the Web, your computer is no longer merely the box on your desk. It becomes part of a single, massive international computer system with a single goal: transferring money out of your bank account. Even so, it retains all the features and abilities you expect from a computer—an Internet connection only makes it even more powerful.

The Internet is more an idea than a physical form. Picture it as a spider web anchored to each and every computer in the world.

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