Saturday, March 5, 2011

Computer Hardware Components

Before you can jump into any discussion about personal computers, you have to speak the language. You can't talk intelligently about anything if you don't know what you're talking about. You need to know the basic terms and buzzwords so you don't fall under some charlatan's spell.

Every PC is built from an array of components, each of which serves a specific function in making the overall machine work. As with the world of physical reality, a PC is built from fundamental elements combined together. Each of these elements adds a necessary quality or feature to the final PC. These building blocks are hardware components, built of electronic circuits and mechanical parts to carry out a defined function. Although all of the components work together, they are best understood by examining them and their functions individually. Consequently this book is divided into sections and chapters by component.

Over the years of the development of the PC, the distinctions between many of these components have turned out not to be hard and fast. In the early days of PCs, most manufacturers followed the same basic game plan using the same components in the same arrangement, but today greater creativity and diversity rules. What once were separate components have merged together; others have been separated out. Their functions, however, remain untouched. For example, although modern PCs may lack the separate timer chips of early machines, the function of the timer has been incorporated into the support circuitry chipsets.

For purposes of this book and discussion, we'll divide the PC into several major component areas, including the system unit, the mass storage system, the display system, peripherals, and connectivity features. Each of these major divisions can be, in turn, subdivided into the major components (or component functions) required in a complete PC.
System Unit

The part of a PC that most people usually think of as the computer-the box that holds all the essential components except, in the case of desktop machines, the keyboard and monitor-is the system unit. Sometimes called CPU-for Central Processing Unit, a term also used to describe microprocessors as well as mainframe computers-the system unit is the basic computer component. It houses the main circuitry of the computer and provides 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 of these external components into one but is usually called simply the computer rather than the system unit or CPU.

One of the primary functions of the system unit is physical. It gives everything in your computer a place to be. It provides the mechanical mounting for all the internal components that make up your computer, including the motherboard, disk drives and expansion boards. The system unit is the case of the computer that you see and everything that is inside it. The system unit supplies power to operate the PC and its internal expansion, disk drives, and peripherals.

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, 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 holds the most important elements of your PC, those that define its function and expandability. These include the microprocessor, BIOS, memory, mass storage, expansion slots, and ports.

The most important of the electronic components on the motherboard is the microprocessor. It does the actual thinking inside the computer. Which microprocessor, of the dozens currently available, determines not only the processing power of the computer but also what software language it understands (and thus what programs it can run).

Many older computers also had a coprocessor that added more performance to the computer on some complex mathematical problems such as trigonometric functions. Modern microprocessors generally internally incorporate all the functions of the coprocessor.

Just as you need your hands and workbench to hold tools and raw materials to make things, your PC'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. Usually located on the motherboard, your PC's microprocessor needs memory to carry out its calculations. 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 that 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.

A computer needs a software program to work. It even needs a simple program just to turn itself on and be able to load and read software. The Basic Input/Output System or BIOS of a computer is a set of permanently recorded program routines that gives the system its fundamental operational characteristics, including instructions telling the computer how to test itself every time it is turned on.

In older PCs, the BIOS determines what the computer can do without loading a program from disk and how the computer reacts to specific instructions that are part of those disk-based programs. Newer PCs may contain simpler or more complex BIOSes. A BIOS can be as simple as a bit of code telling the PC how to load the personality it needs from disk. Some newer BIOSes also include a system to help the machine determine what options you have installed and how to get them to work best together.

At one time, the origins of a BIOS determined the basic compatibility of a PC. Newer machines-those made in the last decade-are generally free from worries about compatibility. The only compatibility issue remaining is whether a given BIOS supports the Plug-and-Play standard that allows automatic system configuration (which is a good thing to look for in a new PC but its absence is not fatal in older systems).

Modern operating systems automatically replace the BIOS code with their own software as soon as your PC boots up. For the most part, the modern BIOS only boots and tests your PC, then steps out of the way so that your software can get the real work done.
Support Circuits

The support circuitry on your PC's motherboard links its microprocessor to the rest of the PC. A microprocessor, although the essence of a computer, is not a computer in itself (if it were, it would be called something else, such as a computer). The microprocessor requires additional circuits to bring it to life: clocks, controllers, and signal converters. Each of these support circuits has its own way of reacting to programs, and thus helps determine how the computer works.

In today's PCs, all of the traditional functions of the support circuitry have been squeezed into chipsets, which are relatively large integrated circuits. In that most PCs are now based on a small range of microprocessors, their chipsets distinguish their motherboards and performance as much as do their microprocessors. In fact, for some folks the choice of chipset is a major purchasing criterion.
Expansion Slots

Exactly as the name implies, the expansion slots of a PC allow you to expand its capabilities by sliding in accessory boards, cleverly termed expansion boards. The slots are spaces inside the system unit of the PC that provide special sockets or connectors to plug in your expansion boards. The expansion slots of notebook PCs accept modules the size of credit cards that deliver the same functions as expansion boards.

The standards followed by the expansion slots in a PC determine both what boards you can plug in and how fast the boards can perform. Over the years, PCs have used several expansion slot standards. In new PCs, the choices have narrowed to three-and you might want all of them in your next system.
Mass Storage

To provide your computer with a way to store the huge amounts of programs and data that it works with every day, your PC uses mass storage devices. In nearly all of today's computers, the primary repository for this information is a hard disk drive. Floppy disks and CD ROM drives give you a way of transferring programs and data to (and from) your PC. One or more mass storage interfaces link the various storage systems to the rest of your PC. In modern systems, these interfaces are often part of the circuitry of the motherboard.
Hard Disk Drives

The basic requirements of any mass storage system are speed, capacity, and low price. No technology delivers as favorable a combination of these virtues as the hard disk drive, now a standard part of nearly every PC. The hard disk drive stores all of your programs and other software so that they can be loaded into your PC's memory almost without waiting. In addition, the hard disk also holds all the data you generate with your PC so that you can recall and reuse it whenever you want. In general, the faster the hard disk and the more it can hold, the better.

Hard disks also have their weaknesses. Although they are among the most reliable mechanical devices ever made-some claim to be able to run for 30 years without a glitch-they lack some security features. The traditional hard disk is forever locked inside your PC, and that makes the data stored on it vulnerable to any evil that may befall your computer. A thief or disaster can rob you of your system and your data in a single stroke. Just as you can't get the typical hard disk out of your PC to store in a secure place, the hard disk gives you no easy way to put large blocks of information or programs into your PC.
CD ROM Drives

Getting data into your PC requires a distribution medium, and when you need to move megabytes, the medium of choice today is the CD ROM drive. Software publishers have made the CD ROM their preferred means of getting their products to you. A single CD that costs about the same as a floppy disk holds hundreds of times more information and keeps it more secure. CD's are vulnerable to neither random magnetic fields nor casual software pirates. CD ROM drives are a necessary part of all multimedia PCs, which means just about any PC you'd want to buy today.

The initials stand for Compact Disc, Read-Only Memory, which describe the technology at the time it was introduced for PC use. Although today's CD ROMs are based on the same silver laser-read discs that spin as CDs in your stereo system, they are no longer read-only and soon won't be mere CDs. Affordable drives to write your own CDs with computer data or stereo music are readily available. Many makers of CD ROM drives are now shifting to the DVD (Digital Video Disc) standard to give their products additional storage capacity.
Floppy Disk Drives

Inexpensive, exchangeable, and technically unchallenging, the floppy disk was the first, and at one time only, mass storage system of many PCs. Based on well-proven technologies and mass produced by the millions, the floppy disk provided the first PCs with a place to keep programs and data and, over the years, served well as a distribution system through which software publishers could make their products available.

In the race with progress, however, the simple technology of the floppy disk has been hard-pressed to keep pace. The needs of modern programs far exceed what floppy disks can deliver, and other technologies (like those CD ROM drives) provide less expensive distribution. New incarnations of floppy disk technology that pack 50 to 100 times more data per disk hold promise but at the penalty of a price that will make you look more than twice at other alternatives.

All that said, the floppy disk drive remains a standard part of all but a few highly specialized PCs, typically those willing to sacrifice everything to save a few ounces (sub-notebooks) and those that need to operate in smoky, dusty environments that would make Superman cringe and Wonder Woman cough.
Tape Drives

Tape is for backup, pure and simple. It provides an inexpensive place to put your data just in case-in case some light-fingered freelancer decides to separate your PC from your desktop, in case the fire department hoses to death everything in your office that the fire and smoke failed to destroy, in case you think DEL *.* means "display all file names," in case that nagging head cold turns out to be a virus that infects your PC and formats your hard disk, in case your next-door neighbor bewitches your PC and turns it into a golden chariot pulled by a silver charger that once was your mouse, in case an errant asteroid ambles through your roof. Having an extra copy of your important data helps you recover from such disasters and those that are even less likely.

Computer tape drives work on the same principles as the cassette recorder in your stereo. Some are, in fact, cassette drives. All such drives use tape as an inexpensive medium for storing data. All modern tape systems put their tape into cartridges that you can lock safely away or send across the continent. And all are slower than you'd like and less reliable than you'd suspect. Nevertheless, tape remains the backup medium of choice for most people who choose to make backups.
Display Systems

Your window into the mind of your PC is its display system, the combination of a graphics adapter or video board and a monitor or flat-panel display. The display system gives your PC the means to tell you what it is thinking, 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 PC to built 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.
Graphics Adapters

Your PC's graphics adapter forms the image that you will see on your monitor screen. It converts digital code into a bit pattern that maps each dot that you'll see. Because it makes the actual conversion, the graphics adapter determines the number of colors that can appear on your monitor as well as the ultimate resolution of the image. In other words, the graphics adapter sets the limit on the quality of the images your PC can produce. Your monitor cannot make an image any better than what comes out of the graphics adapter. The graphics adapter also determines the speed of your PC's video system; a faster board will make smoother video displays.

Many PCs now include at least a rudimentary form of graphics adapter in the form of display electronics on their motherboards; others put the display electronics on an expansion board.

The monitor is the basic display system that's attached to most PCs. Monitors are television sets with Michael Millken's appetite for money. While a 21-inch TV might cost $300 in your local appliance store, the same size monitor will likely cost $2000 and still not show the movies you rent.

Although both monitor and television are based on the same aging technology, one which dates back to the 1920's, they have different aims. The monitor makes more detail, the television sets its sights on the mass market and makes up for its shortcomings in volume. In any case, both rely on big glass bottles coated with glowing phosphors that shine bright enough to light a room.

The quality of the monitor attached to your PC determines the quality of the image you see. Although it cannot make anything look better than what's in the signals from your graphics adapter, it can make them look much worse and limit both the range of colors and the resolution (or sharpness) of the images.
Flat Panel Display Systems

Big, empty bottles are expensive to make and delicate to move. Except for a select elite, most engineers have abjured putting fire-filled bottles of any kind in their circuit designs, the picture tube being the last remnant of this ancient technology. Replacing it are display systems that use solid-state designs based on liquid crystals. Lightweight, low in power requirements, and generally shock and shatter resistant, LCD panels have entirely replaced conventional monitors in notebook PCs and promise to take over desktops in the coming decade. Currently, they remain expensive (several times the cost of a picture tube) and more limited in color range, but research into flat panel systems is racing ahead, while most labs have given up picture tube technology as dead.

The accessories you plug into your computer are usually called peripherals. The name is a carryover from the early beginnings of computers when the parts of a computer that did not actually compute were located some distance from the central processing unit, on the periphery, so to speak.

Today's PCs have two types of peripherals, the internal and external. Internal peripherals fit inside the system unit and usually directly connect to its expansion bus. External peripherals are physically separate from the system unit, connect to the port connectors on the system unit, and often (but not always) require their own source of power. Although the keyboard and monitor of a PC fit the definition of external peripherals, they are usually considered to be part of the PC itself and not peripherals.
Input Devices

You communicate with your PC, telling it what to do, using two primary input devices, the keyboard and the mouse. The keyboard remains the most efficient way to enter text into applications, faster than even the most advanced voice recognition systems that let you talk to your PC. The mouse-more correctly termed a pointing device to include mouse-derived devices such as trackballs and the proprietary devices used by notebook PCs-relays graphic instructions to your computer, letting you point to your choices or sketch, draw, and paint. If you want to sketch images directly onto your monitor screen, a digitizing tablet works more as you would with a pen.

To transfer images to your PC, a scanner copies graphics into bit-images. With the right software, it becomes an optical character recognition, or OCR system, that reads text and transforms words into electronic form.

A voice recognition or voice input system tries to make sense out of your voice. It uses a microphone to turn the sound waves of your voice into electrical signals, a processing board that makes those signals digital, and sophisticated software that attempts to discern the individual words you've spoken from the digital signal.

The electronic thoughts of a PC 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 print-out on paper, solves the problem. And the printer makes your hard copy.

More than any other aspect of computing, printer technology has transformed the industry in the last decade. Where printers were once the clamorous offspring of typewriters, they've now entered the space age with jets and lasers. The modern PC printer is usually a high speed, high quality laser printer that creates four or more pages per minute at a quality level that rivals commercial printing. Inkjet printers sacrifice the utmost in speed and quality for lower cost and the capability of printing color without depleting the green in your budget.

The real useful work that PCs do involves not just you but also the outside world. The ability of a PC to send and receive data to different devices and computers is called connectivity. Your PC can link to any of a number of hardware peripherals through its input/output ports. Better still, through modems, networks, and related technologies it can connect with nearly any PC in the world.
Input/Output Ports

Your PC links to its peripherals through its input and output ports. Every PC needs some way of acquiring information and putting it to work. Input/output ports are the primary route for this information exchange. In the past, the standard equipment of most PCs was simple and almost pre-ordained-one serial port and one parallel port, typically as part of the motherboard circuitry. 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) while the Infrared Data Association (IrDA) system provides wireless links. Similarly the simple parallel port has become an external expansion bus capable of linking dozens of devices to a single jack.

To connect with other PCs and information sources such as the Internet through the international telephone system, you need a modem. Essentially a signal converter, the modem adapts your PC's data to a form compatible with the telephone system.

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 such as digital telephone services (like ISDN), 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.

Any time you link two or more PCs together, you've made 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).

Once you link up to the World Wide Web, your computer is no longer merely the box on your desk. Your PC becomes part of a single, massive international computer system. Even so, it retains all the features and abilities you expect from a PC-it only becomes even more powerful.

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