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.
Processing
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.
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.
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.
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.
Communicating
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
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.
Telecommunications
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.
Internet
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.
Remembering
No matter how smart you are, you wouldn’t know anything if you couldn’t remember. Thoughts and ideas would go in one neuron and out another, forever lost in the entropy of the universe. You know things because you can call back thoughts and ideas, to work on them again or just talk about them. A computer, too, needs some way of retaining its thoughts. Like you, it needs both short-term memory for holding ideas while it works on them and long-term memory to store all the facts and old ideas that, by chance, it might need another day.
The short-term memory of computers is often called simply memory. The long-term memory is often termed mass storage and involves several technologies. Hard disk drives hold the ideas you put into the computer, both commercial programs and your own original data. Floppy disks and optical drives (CDs and DVDs for the most part) store the ideas of others than you want your computer to access. Tape drives provide a safety net, keeping a duplicate copy of your computer’s most important ideas.
Memory
Just as you need your hands and workbench to hold tools and raw materials to make things, your computer’s microprocessor needs a place to hold the data it works on and the tools to do its work. Memory, which is often described by the more specific term RAM (which means Random Access Memory), serves as the microprocessor’s workbench. The amount and architecture of the memory of a system determines how it can be programmed and, to some extent, the level of complexity of the problems it can work on. Modern software often requires that you install a specific minimum of memory—a minimum measured in megabytes—to execute properly. With modern operating systems, more memory often equates to faster overall system performance.
In today’s computers, memory usually comes in subassemblies called memory modules that plug into special sockets on the main circuit board of your computer. Most computers have three or more of these sockets in a group, one or more of which is filled with a memory module as standard equipment.
Hard Disk Drives
Long-term memory is where you store thoughts and ideas that, although you don’t need them immediately, you need to know—stuff like your shoe size, which doesn’t come up in everyday conversation (at least not among normal adults) but becomes a handy factoid when musing through a mail-order catalog. Your computer’s hard disk holds such factoids along with all the other stuff it needs to know but not at this exact moment—such as the instructions for programs you’re not using, financial records you hope the auditor will ignore, term papers you someday hope to publish as best-selling fiction, and even extra designs for wallpaper for your computer screen. Your computer’s hard disk lets you call on any of those stored facts on a microsecond’s notice.
Most hard disks take the form of a sealed box, typically silver and black with a green circuit board dotted with tiny electrical components on the bottom. A hard disk connects to the main circuit board of your computer through that interface we talked about earlier via a short, wide, and flat set of wires, called a ribbon cable because it looks like a ribbon (although an admittedly strange gray ribbed ribbon).
Floppy Disk Drives
Once upon a time, some computers lacked hard disk drives and instead used floppy disk drives (“once upon a time” being in the unbelievable past, a little before Cinderella cleaned out fireplaces). Inexpensive, exchangeable, and technically unchallenging, the floppy disk served as a data interchange system for years because it was based on well-proven technologies and was mass produced by the millions.
Today, the floppy disk drive is found on nearly every computer, but functionally it’s about as useful to your computer as an appendix. (Granted, an appendix won’t fit into a drive slot, but you get the idea.) In today’s world the floppy disk is slow and holds too little information, so it is gradually disappearing from computers, replaced in function by any of a variety of optical drives.
The computers that still have floppy disk drives usually wear them proudly, out in front. On desktop systems, it’s usually the uppermost drive in the case. From the outside you see only a long, black slot about three-and-a-half inches wide with a rectangular button near one corner. Notebook computers put their floppy disk drives, if they have one, wherever they fit—usually hidden in the side of the computer under the keyboard.
Optical Drives
Getting new memories into your computer is the primary job served by optical drives. They store programs and data in a convenient form—small discs—that’s standardized so that you can exchange the discs (and memories) between computers. (Note that due to a strange quirk of design and origin, magnetic drives use “disks” whereas optical drives use “discs.”)
Optical discs currently come in two flavors: Compact Discs and Digital Versatile Discs. These are the CDs and DVDs you slide into your home entertainment system. In either form, discs are cheap and easy to copy, so software publishers have made the CD-ROM their preferred means of getting their products to you, with DVDs slowly replacing CD-ROMs because of their higher capacity. You can create your own optical disks with a suitable drive to store either data for your computer or music and video for your entertainment systems.
A CD-ROM or DVD drive is usually the other drive on the front of your desktop computer, bigger than the floppy and featuring a volume control and headphone jack (should you want to slide a music CD into the drive). You’ll know what it is as soon as you press the eject button and the tray rolls out. On a notebook computer, manufacturers stuff their optical drives wherever they fit, usually on the side near the back of the computer.
Tape Drives
Tape is for backup, pure and simple. It provides an inexpensive place to put your data just in case—just in case some light-fingered freelancer decides to separate your computer from your desktop; just in case the fire department hoses to death everything in your office that the fire and smoke failed to destroy; just in case you empty your Recycle Bin moments before discovering you accidentally deleted all your exculpatory tax records; just in case an errant asteroid ambles through your roof. Having an extra copy of your important data helps you recover from such disasters as well as those that are even less likely to happen.
Tape drives are optional on personal computers. They add enough cost that people would rather risk their data. On larger computers (the servers used in business), tape drives are more common because the cost of restoring data is so high, probably thousands of times the cost of a drive, that their use is justified.
Listening and Monitoring
If you want your computer to do anything useful, you have to be able to tell it what to do. Although some computers actually do listen to you speak using voice-recognition technology, most systems depend on traditional control systems, the keyboard, and the mouse to put you in command. In addition, many applications require that you fill your computer with data—keystrokes, images, and sounds. Your computer acquires this information by electronically listening to any of several input devices—scanners, digital cameras, sound board samplers, and so on.
Your window into the mind of your computer that lets you monitor what it does is its display system, itself a combination of a graphics adapter or video board and a monitor or flat-panel display. The display system gives your computer the means to tell you what it is thinking and to show you your data in the form that you best understand—be it numbers, words, or pictures. The two halves of the display system work hand in hand. The graphics adapter uses the digital signals inside your computer to build an electronic map of what the final image should look like, storing the data for every dot on your monitor in memory. Electronics generate the image that appears on your monitor screen.
Keyboard
The keyboard remains the most efficient way to enter text into applications, faster than even the most advanced voice-recognition systems, which let you talk to your computer. Scientists believe that keyboarding is a more direct route from your brain. Speaking requires more work, and the mechanics of sounding your voice take more time. But the keyboard lets you do more than mere typing. It is the primary command-and-control center for your computer.
The keyboard is probably the most identifiable part of any computer. You can’t miss an array of over 100 buttons meant to be individually activated by your fingers. They come built into notebook computers, tethered on short cords to most desktop systems, and warped and bent in magnificent curves meant to soothe tired hands.
Pointing Devices
Although computers once recognized only text—for which a keyboard sufficed—today’s computers work with pictures (what computer-people call graphics). The keyboard is notoriously poor at picking out pieces of pictures, but the mouse—more correctly termed a pointing device to include mouse-derived devices such as trackballs and the proprietary devices used by notebook computers—readily relays graphic instructions to your computer. Not only can the pointing device point, but it also lets you draw, sketch, and paint.
The most familiar pointing device is the hand-size mouse that you move around your desktop to cause a mouse pointer to move analogously on the screen. But some people prefer upside-down mice called trackballs for rolling the pointer around. Notebook computers use specialized pointing devices called pointing sticks (IBM’s TrackPoint is the premier example) or touchpads, which let you move around the desktop by scratching your finger across a plastic pad.
Scanners
The range of input devices naturally grows to embrace whatever kind of information you want to get into your computer. Say you have on-paper images you want to capture—drawings your kids made in first grade, your likeness on a poster from the post office, portraits of presidents on small sheets of paper—so that you can get into your graphics program to clean them up. Engineers developed the scanner to do just that. A scanner dissects the image into bits of graphic information like little dots that your computer can manipulate and store digitally.
Although engineers have developed an entire zoo of scanners to suit different kinds of original material (for example, photos or documents), most of today’s scanners prefer to look at flat sheets. They take the form of flat boxes with glass plates on top, on which you lay printed images that you want to capture to your computer.
Digital Cameras
Scanners work when you have an image already fixed on paper, but when you want to get something you see in the real world into computer-compatible form, you need a digital camera. As with a scanner, a digital camera reduces an image—in this case, a scene you see in the real world—into tiny dots that your computer can store as digital data. The digital camera is a completely self-contained system for capturing and saving real-world images. It works with and without a computer, but the full power of the digital camera is realized best when you can edit its images with software on your computer.
A digital camera looks and works much like old-time film cameras with a lens in front and a viewfinder to help you frame the scenes you want to save. Some digital cameras are as simple as old box cameras—press a button and let the camera do the rest. Others have more controls than a small space shuttle, letting you unleash your full creative powers.
Display Systems
Your computer’s thoughts, like your own, are invisible. Making your thoughts visible to others is what language and art are all about. The computer’s equivalent is the graphics adapter. This component takes the digital thoughts of your computer and turns them into an electronic image, essentially a picture saved in the computer’s electronic memory.
Once a graphics adapter has an image in this form—be it a page of text or a picture of an oasis—a monitor (sometimes called a display) connected to your computer makes the actual image that you can see. Monitors are essentially television sets built to military specifications. They produce sharper, higher-quality images than any television (including a new digital, high-resolution models) can hope to show.
Almost any monitor will let you work with your desktop computer (the monitor is built in to notebook machines), but the quality of the monitor attached to your computer determines the quality of the image you see and, often, of the work you do. Although no monitor can make anything look better than what’s in the signals from your graphics adapter, a bad monitor can make them look much worse and limit both the range of colors and the resolution (or sharpness) of the images.
In most desktop computers, the graphics adapter is an expansion board, often the only one that comes as factory equipment, although notebook computers and many desktop systems have their graphics adapter functionality built in to the circuitry of the main circuit boards. Modern monitors for desktop computers come in two types: Cathode-ray tube (CRT) monitors use picture tubes like old-fashioned television sets and are big boxes that sit on your desk and, often, crowd everything off. Flat-panel monitors use liquid-crystal displays (LCDs) that run cooler and take up less room than CRTs (but cost substantially more). Either type is tethered to a desktop computer by a short cable. Notebook computers universally have built-in flat-panel displays.
Audio
A pretty picture is not enough in today’s world. You need a total experience, one that involves both pictures and sound. After all, silent films went out of date in 1927. Consequently, every computer now has a sound system. In business computers, it’s often nothing more than a beeper to warn you when you’ve pressed the wrong key. In most of today’s computers, however, the sound system is on par with those in theaters (only not as loud). They can generate any sound you can hear and make it appear to be anywhere in the room.
Speakers are the most obvious part of any sound system, if just because you’ve got to find a place for two or three more boxes on your office desk. The real sound-generating capability of a computer comes from its sound board, however, which either slides into an expansion slot in the computer or is built into its main circuitry.
Printers
The electronic thoughts of a computer are notoriously evanescent. Pull the plug and your work disappears. Moreover, monitors are frustratingly difficult to pass around and post through the mail when you want to show off your latest digital art creation. Hard copy (the printout on paper) solves this problem. A printer is the device of choice for making hard copy from your computer’s thoughts.
Printers come in many varieties. The most common are laser printers and inkjet printers. Either is a box with two paper trays that connects to your computer with a short cord. Lasers make fast, cheap, black-and-white pages. Inkjets are low-cost printers that excel at printing color but do so at a higher price per page because of their use of expensive inks.
Fax
Fax combines both the telecommunications capability of a modem with the hard-copy output of a printer. In effect, a fax machine becomes a remote printer for your computer—a system that allows your computer to print remotely to anywhere in the world you can get a telephone connection.
Today, fax is an invisible part of nearly every modem. If you can get online through a dial-up connection with your computer, you can fax. In most cases, you need nothing more than the modem already in your computer. The only addition required is invisible software.
Infrastructure
Infrastructure is what holds your computer together. It is the overall form of your computer, the substrate that it is built upon, and the essential supplies required to make it run. The substrate of the modern computer is the motherboard (or system board or main board) coupled with the expansion boards plugged into it. The case provides the basic form of the computer. And the one essential service required by any modern computer is power, the electricity used in the computer’s logic operations.
Motherboards
The centerpiece of the system unit is the motherboard. All the other circuitry of the system unit is usually part of the motherboard or plugs directly into it. The electronic components on the motherboard carry out most of the function of the machine—running programs, making calculations, and even arranging the bits that will display on the screen. Because the motherboard defines each computer’s functions and capabilities and because every computer is different, it only stands to reason that every motherboard is different, too. Not exactly. Many different computers have the same motherboard designs inside. And oftentimes a single computer model might have any of several different motherboards, depending on when it came down the production line (and what motherboard the manufacturer got the best deal on).
The motherboard is the main circuit board in nearly every computer—desktop or laptop. Usually it lines the bottom of the case like thick, green shelf-paper decorated with lines and blobs that could be a Martian roadmap.
Expansion Boards
Expansion boards are the physical form of the expansion devices that connect to your computer through its expansion slots. They are simply circuit boards that are smaller than the motherboard.
However, they are not just any circuit boards. Expansion boards must follow strict standards as to size, signals, power consumption, and software interface to ensure that they will work inside any given computer. Although at one time nearly all computers used Industry Standard Architecture (ISA) for their expansion boards, the modern replacement is Peripheral Component Interconnect (PCI). Some desktop computers don’t allow the use of expansion boards at all. Notebook machines use PC cards instead.
Power
Every computer requires a continuous supply of carefully conditioned direct current at low voltage, well below that available at your wall outlet. Although batteries can provide this power for portable computers, desktop units require power supplies to convert house current into computer current. Similarly, power supplies charge and substitute for portable computer batteries.
Bringing power to your computer also imports danger, however, and your computer requires protection from glitches on the power line. Surge suppressors and backup power systems help to ensure that your computer gets the proper electrical diet.
The power supply in most desktop computers is locked for your protection in a steel box inside your computer’s case. It keeps your hands out of harm’s way if you dig into your computer to add an expansion board or other accessory. Notebook computers put much of the function of the power supply into their external “bricks” that plug directly into a wall outlet. The output of the brick is at a voltage that’s safe should you accidentally encounter it (and safe for your notebook computer, as well).
Cases
The case is what most people think of as the entire computer, ignoring all the essential parts attached by cables and often the individual components inside. The main box goes by a special name, system unit, because it is the heart of the system. Some people call it the CPU (central processing unit), although that term is also (and confusingly) used for the microprocessor inside. The system unit houses the main circuitry of the computer and provides spaces called bays for internal disk drives as well as a place for the jacks (or outlets) that link the computer to the rest of its accouterments, including the keyboard, monitor, and peripherals. A notebook computer combines all these external components into one unit, but it’s usually called simply the “computer” rather than system unit or CPU.
The case is more than a box. It’s also a protective shell that keeps the dangers of the real world away from the delicate electronics of the computer. What’s more, it protects the world from interference from the signals of the computer. The case is also part of a cooling system (which may include one or more fans) that keeps the electronics inside cool for longer life.
The case of a modern computer can take many forms—from small-footprint desktop computers to maxi-tower computers, from compact sub-notebook computers (or even handheld computers) to huge, almost unportable desktop-replacement notebook computers. In desktop systems, the size more than anything else determines how many accessories you can add to your system—and how much of your home or office you have to give up to technology. Weight, more than size, is the limiting physical factor for notebook computers. How much you want to carry often determines how many features you get.