PC Components, Features, and System Design

PC Components,Features, and

System Design

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26 Chapter 2 PC Components, Features, and System Design

What Is a PC?I normally ask the question, “What exactly is a PC?” when I begin one of my PC hardware seminars.Of course, most people immediately answer that PC stands for personal computer, which in fact it does.They might then continue by defining a personal computer as any small computer system purchasedand used by an individual. Unfortunately, that definition is not nearly precise or accurate enough forour purposes. I agree that a PC is a personal computer, but not all personal computers are PCs. Forexample, an Apple Macintosh system is clearly a personal computer, but nobody I know would call aMac a PC, least of all Mac users! For the true definition of what a PC is, you must look deeper.

Calling something a PC implies that it is something much more specific than just any personal com-puter. One thing it implies is a family relation to the original IBM PC from 1981. In fact, I’ll go so far asto say that IBM literally invented the type of computer we call a PC today; that is, IBM designed and cre-ated the very first one, and IBM originally defined and set all the standards that made the PC distinctivefrom other personal computers. Note that it is very clear in my mind—as well as in the historicalrecord—that IBM did not invent the personal computer. (Most recognize the historical origins of the per-sonal computer in the MITS Altair, introduced in 1975.) So, IBM did not invent the personal computer,but it did invent what today we call the PC. Some people might take this definition a step further anddefine a PC as any personal computer that is “IBM compatible.” In fact, many years back, PCs werecalled either IBM compatibles or IBM clones, in essence paying homage to the origins of the PC at IBM.

The reality today is that although IBM clearly designed and created the first PC in 1981 and con-trolled the development and evolution of the PC standard for several years thereafter, IBM is nolonger in control of the PC standard; that is, it does not dictate what makes up a PC today. IBM lostcontrol of the PC standard in 1987 when it introduced its PS/2 line of systems. Up until then, othercompanies that were producing PCs literally copied IBM’s systems right down to the chips; connec-tors; and even the shapes (form factors) of the boards, cases, and power supplies. After 1987, IBMabandoned many of the standards it created in the first place. That’s why for many years now I haverefrained from using the designation “IBM compatible” when referring to PCs.

If a PC is no longer an IBM-compatible system, what is it? The real question seems to be, “Who is incontrol of the PC standard today?” That question is best broken down into two parts. First, who is incontrol of PC software? Second, who is in control of PC hardware?

Who Controls PC Software?Most of the people in my seminars don’t even hesitate for a split second when I ask this question;they immediately respond, “Microsoft!” I don’t think there is any argument with that answer.Microsoft clearly controls the operating systems used on PCs, which have migrated from the originalMS-DOS to Windows 3.1/95/98/Me, Windows NT/2000, and now Windows XP.

Microsoft has effectively used its control of the PC operating system as leverage to also control othertypes of PC software, such as utilities and applications. For example, many utility programs originallyoffered by independent companies, such as disk caching, disk compression, file defragmentation, filestructure repair, and even simple applications such as calculator and notepad programs, are now bun-dled in (included with) Windows. Microsoft has even bundled more comprehensive applications such asWeb browsers, ensuring an automatic installed base for these applications—much to the dismay of com-panies who produce competing versions. Microsoft has also leveraged its control of the operating systemto integrate its own networking software and applications suites more seamlessly into the operating sys-tem than others. That’s why it now dominates most of the PC software universe, from operating systemsto networking software to utilities, from word processors to database programs to spreadsheets.

In the early days of the PC, when IBM was clearly in control of the PC hardware standard, it hiredMicrosoft to provide most of the core software for the PC. IBM developed the hardware, wrote thebasic input/output system (BIOS), and then hired Microsoft to develop the disk operating system

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What Is a PC? 27

(DOS), as well as several other programs and utilities for the PC. In what was later viewed as perhapsthe most costly business mistake in history, IBM failed to secure exclusive rights to the DOS it hadcontracted from Microsoft, either by purchasing it outright or by an exclusive license agreement.Instead, IBM licensed it nonexclusively, which subsequently allowed Microsoft to sell the same MS-DOS code it developed for IBM to any other company that was interested. Early PC cloners suchas Compaq eagerly licensed this same operating system code, and suddenly consumers could purchasethe same basic MS-DOS operating system with several different company names on the box. In retro-spect, that single contractual error made Microsoft into the dominant software company it is todayand subsequently caused IBM to lose control of the very PC standard it had created.

As a writer myself (of words, not software), I can appreciate what an incredible oversight this was.Imagine that a book publisher comes up with a great idea for a very popular book and then contractswith and subsequently pays an author to write it. Then, by virtue of a poorly written contract, theauthor discovers that he can legally sell the very same book (perhaps with a different title) to all thecompetitors of the original publisher. Of course, no publisher I know would allow this to happen; yetthat is exactly what IBM allowed Microsoft to do back in 1981. By virtue of its deal with Microsoft,IBM had essentially lost control of the software it commissioned for its new PC from day one.

It is interesting to note that in the PC business, software enjoys copyright protection, whereas hardwarecan be protected only by patents, which are difficult, time-consuming, and expensive to get and whichalso expire after 17 years. To patent something requires that it be a unique and substantially new design.This made it impossible to patent most aspects of the IBM PC because it was designed using previouslyexisting parts that anybody could purchase off the shelf! In fact, most of the important parts for theoriginal PC came from Intel, such as the 8088 processor, 8284 clock generator, 8253/54 timer, 8259interrupt controller, 8237 DMA (direct memory access) controller, 8255 peripheral interface, and 8288bus controller. These chips made up the heart and soul of the original PC motherboard.

Because the design of the original PC was not wholly patentable, anybody could duplicate the hardwareof the IBM PC. All she had to do was purchase the same chips from the same manufacturers and suppli-ers IBM used and design a new motherboard with a similar circuit. Seemingly as if to aid in this, IBMeven published complete schematic diagrams of its motherboards and all its adapter cards in verydetailed and easily available technical reference manuals. I have several of these early IBM manuals andstill refer to them from time to time for specific component-level PC design information. In fact, I stillrecommend these original manuals to anybody who wants to delve deeply into PC hardware design.

The difficult part of copying the IBM PC was the software, which is protected by copyright law.Phoenix Software (today known as Phoenix Technologies) was among the first to develop a legal wayaround this problem, which enabled it to functionally duplicate (but not exactly copy) software suchas the BIOS. The BIOS is defined as the core set of control software that drives the hardware devices inthe system directly. These types of programs are normally called device drivers, so in essence, the BIOSis a collection of all the core device drivers used to operate and control the system hardware. Theoperating system (such as DOS or Windows) uses the drivers in the BIOS to control and communicatewith the various hardware and peripherals in the system.

◊◊ See Chapter 5, “BIOS,” p. 397.

Phoenix’s method for legally duplicating the IBM PC BIOS was an ingenious form of reverse-engineering.It hired two teams of software engineers, the second of which had to be specially screened to consistonly of people who had never before seen or studied the IBM BIOS code. The first team did study theIBM BIOS and wrote as complete a description of what it did as possible. The second team read thedescription written by the first team and set out to write from scratch a new BIOS that did everything thefirst team described. The end result was a new BIOS written from scratch with code that, although notidentical to IBM’s, had exactly the same functionality.

Phoenix called this a “clean room” approach to reverse-engineering software, and it can escape any legalattack. Because IBM’s original PC BIOS consisted of only 8KB of code and had limited functionality,

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duplicating it through the clean room approach was not very difficult nor time-consuming. As the IBMBIOS evolved, Phoenix—as well as the other BIOS companies—found that keeping up with any changesIBM made was relatively easy. Discounting the power on self test (POST) or BIOS Setup program (used forconfiguring the system) portion of the BIOS, most motherboard BIOSs, even today, have only about32KB–128KB of active code. Today, Phoenix and American Megatrends (AMI) are the leading developers ofBIOS software for PC system and motherboard manufacturers. A third major producer of BIOS software,Award Software, is owned by Phoenix Technologies, which continues to sell Award BIOS–based products.

After the hardware and BIOS of the IBM PC were duplicated, all that was necessary to produce a fullyIBM-compatible system was DOS. Reverse-engineering DOS, even with the clean room approach,would have been a daunting task because DOS is much larger than the BIOS and consists of manymore programs and functions. Also, the operating system has evolved and changed more often thanthe BIOS, which by comparison has remained relatively constant. This means that the only way to getDOS on an IBM compatible was to license it. This is where Microsoft came in. Because IBM (who hiredMicrosoft to write DOS in the first place) did not ensure that Microsoft signed an exclusive licenseagreement, Microsoft was free to sell the same DOS it designed for IBM to anybody else who wanted it.With a licensed copy of MS-DOS, the last piece was in place and the floodgates were open for IBM-compatible systems to be produced whether IBM liked it or not.

In retrospect, this is exactly why there are no clones or compatibles of the Apple Macintosh system. Itis not that Mac systems can’t be duplicated; in fact, Mac hardware is fairly simple and easy to produceusing off-the-shelf parts. The real problem is that Apple owns the Mac OS as well as the BIOS, andbecause Apple has seen fit not to license them, no other company can sell an Apple-compatible sys-tem. Also, note that the Mac BIOS and OS are very tightly integrated; the Mac BIOS is very large andcomplex, and it is essentially a part of the OS, unlike the much simpler and more easily duplicatedBIOS found on PCs. The greater complexity and integration has allowed both the Mac BIOS and OS toescape any clean-room duplication efforts. This means that without Apple’s blessing (in the form oflicensing), no Mac clones are likely ever to exist.

It might be interesting to note that during 1996–1997, an effort was made by the more liberatedthinkers at Apple to license its BIOS/OS combination, and several Mac-compatible machines weredeveloped, produced, and sold. Companies such as Sony, Power Computing, Radius, and evenMotorola invested millions of dollars in developing these systems, but shortly after these first Macclones were sold, Apple rudely canceled all licensing! This was apparently the result of an edict fromSteve Jobs, who had been hired back to run the company and who was one of the original architectsof the closed-box, proprietary-design Macintosh system in the first place. By canceling these licenses,Apple has virtually guaranteed that its systems will never be a mainstream success. Along with itssmaller market share come much higher system costs, fewer available software applications, and fewerhardware upgrades as compared to PCs. The proprietary design also means that major repair orupgrade components, such as motherboards, power supplies, and cases, are available only from Appleat very high prices and upgrades of these components are usually not cost effective.

I often think that if Apple had a different view and had licensed its OS and BIOS early on, this bookmight be called Upgrading and Repairing Macs instead!

Who Controls PC Hardware?Although it is clear that Microsoft has always controlled PC software by virtue of its control over the PCoperating system, what about the hardware? It is easy to see that IBM controlled the PC hardware stan-dard up through 1987. After all, IBM invented the core PC motherboard design; the original expansionbus slot architecture (8/16-bit ISA bus); serial and parallel port implementations; video card designthrough VGA and XGA standards; floppy and hard disk interface and controller implementations; powersupply designs; keyboard interfaces and designs; mouse interface; and even the physical shapes (form fac-tors) of everything from the motherboard to the expansion cards, power supplies, and system chassis. Allthese pre-1987 IBM PC, XT, and AT system design features are still influencing modern systems today.

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What Is a PC? 29

But to me the real question is which company has been responsible for creating and inventing newerand more recent PC hardware designs, interfaces, and standards? When I ask people that question, Inormally see some hesitation in their responses—some people say Microsoft (but it controls the soft-ware, not the hardware), and some say Compaq or Dell, or they name a few other big-name systemmanufacturers. Only a few surmise the correct answer—Intel.

I can see why many people don’t immediately realize this; I mean, how many people actually own anIntel-brand PC? No, not just one that says “Intel inside” on it (which refers only to the system havingan Intel processor), but a system that was designed and built by, or even purchased through, Intel.Believe it or not, I think that many—if not most—people today do have Intel PCs!

Certainly this does not mean that consumers have purchased their systems from Intel because Inteldoes not sell complete PCs to end users. You can’t currently order a system from Intel, nor can you pur-chase an Intel-brand system from somebody else. What I am talking about is the motherboard. In myopinion, the single most important part in a PC system is the motherboard, and I’d say that whoevermade your motherboard would be considered the manufacturer of your system. Even back when IBMwas the major supplier of PCs, it primarily made the motherboard and contracted out the other com-ponents of the system (power supply, disk drives, and so on) to others.

◊◊ See “Motherboards and Buses,” p. 201.

Many of the top-selling system manufacturers do design and make their own motherboards. Accordingto Computer Reseller News magazine, the top desktop systems manufacturers for the last several yearshave consistently been names such as HP, Compaq (now owned by HP), and IBM. These companies, forthe most part, do design and manufacture their own motherboards, as well as many other system com-ponents. In some cases, they even design their own chips and chipset components for their ownboards. Although sales are high for these individual companies, a larger overall segment of the marketis what those in the industry call the white-box systems.

White-box is the term used by the industry to refer to what would otherwise be called generic PCs—thatis, PCs assembled from a collection of industry-standard, commercially available components. Thewhite-box designation comes from the fact that historically most of the chassis used by this type of sys-tem have been white (or ivory or beige).

The great thing about white-box systems is that they use industry-standard components that are inter-changeable. This interchangeability is the key to future upgrades and repairs because it ensures that aplethora of replacement parts will be available to choose from and will interchange. For many years, Ihave recommended avoiding proprietary systems and recommended more industry-standard white-boxsystems instead.

Companies selling white-box systems do not really manufacture the systems; they assemble them. That is,they purchase commercially available motherboards, cases, power supplies, disk drives, peripherals, and soon, and assemble and market everything together as complete systems. Dell, Gateway, and Micron (nowMPC) are some of the larger white-box system assemblers today, but hundreds more could be listed. In over-all total volume, this ends up being the largest segment of the PC marketplace today. What is interestingabout white-box systems is that, with very few exceptions, you and I can purchase the same motherboardsand other components any of the white-box manufacturers can (although we would probably pay morethan they do because of the volume discounts they receive). We can assemble a virtually identical white-box system from scratch ourselves, but that is a story for Chapter 22, “Building or Upgrading Systems.”

Note that some of these white-box companies have incredible sales—for example, Dell has taken thetop PC sales spot from Compaq (now HP), who had held it for many years. Gateway and the otherwhite-box system builders are not far behind.

The point of all this is, of course, that if Dell, Gateway, MPC, and others do not manufacture their ownmotherboards, who does? You guessed it—Intel. Not only do those specific companies mainly use Intelmotherboards, if you check around, you’ll find today that many of the systems in the white-box market

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come with Intel motherboards. The only place Intel doesn’t have a presence is the AMD-based systemsdesigned to support Athlon-branded processors.

Although this is an extreme case, one review of 10 systems in Computer Shopper magazine listed 8 out ofthe 10 systems evaluated as having Intel motherboards. In fact, those 8 used the exact same Intel mother-board. Therefore, those systems differed only in the cosmetics of the exterior case assemblies and bywhich peripheral components, such as video card, disk drives, keyboard, and so on, were selected. Thefunny thing was that many of the peripheral items were identical among the systems as well. Before youcompare preassembled systems from different manufacturers, be sure to get a listing of which parts theyare using; you might be surprised to see how similar the systems on the market at any given time can be.

Although Intel still dominates motherboard sales, that dominance has faltered somewhat from a fewyears back. Because of Intel’s focus on Rambus memory during the early Pentium 4 days, many of thelower-cost system builders switched to alternative products. Also, most of Intel’s boards are designed tomake overclocking either impossible or extremely difficult, so “hotrod” system builders typicallychoose non-Intel boards.

AMD, on the other hand, manufactures processors and chipsets but not complete motherboards. Forthat, AMD relies on a number of other motherboard manufacturers to make boards designed to acceptAMD processors. These boards use either the AMD chipsets or other chipsets made by third-party com-panies specifically to support AMD processors. The same motherboard companies making boards forAMD processor–based systems also make motherboards for Intel processor–based systems, in essencecompeting directly with Intel’s own motherboards.

◊◊ See “Chipsets,” p. 239.

How did Intel come to dominate the interior of our PCs? Intel has been the dominant PC processor sup-plier since IBM chose the Intel 8088 CPU in the original IBM PC in 1981. By controlling the processor,Intel naturally controlled the chips necessary to integrate its processors into system designs. This naturallyled Intel into the chipset business. It started its chipset business in 1989 with the 82350 Extended IndustryStandard Architecture (EISA) chipset, and by 1993 it had become—along with the debut of the Pentiumprocessor—the largest-volume major motherboard chipset supplier. Now I imagine Intel sitting there,thinking that it makes the processor and all the other chips necessary to produce a motherboard, so whynot just eliminate the middleman and make the entire motherboard, too? The answer to this, and a realturning point in the industry, came about in 1994 when Intel became the largest-volume motherboardmanufacturer in the world. And Intel has remained solidly on top ever since. It doesn’t just lead in this cat-egory by any small margin; in fact, during 1997, Intel made more motherboards than the next eight largestmotherboard manufacturers combined, with sales of more than 30 million boards, worth more than $3.6billion! Note that this figure does not include processors or chipsets—only the boards themselves. Theseboards end up in the various system assembler brand PCs you and I buy, meaning that most of us are nowessentially purchasing Intel-manufactured systems, no matter who actually wielded the screwdriver.

Intel controls the PC hardware standard because it controls the PC motherboard. It not only makesthe vast majority of motherboards being used in systems today, but it also supplies the vast majorityof processors and motherboard chipsets to other motherboard manufacturers.

Intel also has had a hand in setting several recent PC hardware standards, such as the following:

■ PCI (Peripheral Component Interconnect) local bus interface

■ PCI Express (originally known as 3GIO), the interface elected by the PCI Special Interest Group(PCI SIG) to replace PCI as a high-performance bus for future PCs

■ Accelerated Graphics Port (AGP) interface for high-performance video cards

■ ATX motherboard form factor (and variations such as MicroATX and FlexATX), which, begin-ning in 1996–1997, replaced the (somewhat long-in-the-tooth) IBM-designed Baby-AT form fac-tor that had been used since the early 1980s

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What Is a PC? 31

■ NLX motherboard form factor to replace the proprietary and limited LPX design used by manylower-cost systems, which finally brought motherboard upgradability to those systems

■ Desktop Management Interface (DMI) for monitoring system hardware functions

■ Dynamic Power Management Architecture (DPMA) and Advanced Power Management (APM)standards for managing power use in the PC

Intel dominates not only the PC, but the entire semiconductor industry. According to the sales figurescompiled by iSuppli.com, Intel has more than two and a half times the sales of the next closest semi-conductor company (Samsung) and about nine times the sales of competitor AMD (see Table 2.1).

Table 2.1 Top 30 Semiconductor Companies Ranked by 2002 Semiconductor Sales

2002 2002 2001 2001 2000 2000 Supplier Rank Sales Rank Sales Rank Sales

Intel 1 $23.47 1 $23.54 1 $30.21

Samsung 2 $9.18 4 $6.14 4 $8.94

STMicro 3 $6.31 3 $6.36 6 $7.89

TI 4 $6.20 5 $6.05 3 $9.20

Toshiba 5 $6.19 2 $6.54 2 $10.43

Infineon 6 $5.36 8 $4.56 8 $6.74

NEC 7 $5.26 6 $5.30 5 $8.20

Motorola 8 $4.73 7 $4.83 7 $7.71

Philips 9 $4.36 9 $4.41 9 $6.27

Hitachi 10 $4.05 10 $4.24 12 $5.69

Mitsubishi 11 $3.62 11 $3.87 11 $5.79

IBM 12 $3.39 14 $3.56 18 $3.99

Matsushita 13 $3.28 16 $3.01 17 $4.33

Fujitsu 14 $3.24 13 $3.73 15 $5.01

Micron 15 $3.22 18 $2.45 10 $6.26

AMD 16 $2.61 12 $3.79 16 $4.38

Hynix 17 $2.57 19 $2.34 14 $5.10

Sony 18 $2.50 17 $2.47 20 $3.29

Rohm 19 $2.39 21 $2.21 23 $3.06

Sharp 20 $2.36 20 $3.36 19 $3.33

Sanyo 21 $2.10 22 $2.03 21 $3.28

Agere 22 $2.03 15 $3.14 13 $5.10

Analog Devices 23 $1.94 23 $1.93 24 $2.74

Qualcomm 24 $1.85 28 $1.39 37 $1.22

NVIDIA 25 $1.80 30 $1.29 51 $0.71

Agilent 26 $1.60 24 $1.53 27 $2.31

National 27 $1.57 26 $1.51 25 $2.36

LSI Logic 28 $1.51 25 $1.56 26 $2.34

Fairchild 29 $1.35 29 $1.34 31 $1.68

Atmel 30 $1.21 27 $1.48 29 $2.01

*Dollars in millions

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As you can see by these figures, it is no wonder that a popular industry news Web site called The Register(http://www.theregister.co.uk) uses the term “Chipzilla” when referring to the industry giant.

Whoever controls the operating system controls the software for the PC, and whoever controls theprocessor—and therefore the motherboard—controls the hardware. Because Microsoft and Inteltogether seem to control software and hardware in the PC today, it is no surprise the modern PC isoften called a “Wintel” system.

PC Design GuidesEven though Intel controls PC hardware, Microsoft recognizes its power over the PC from the operat-ing system perspective and has been collaborating with Intel. Together, they have released a series ofdocuments called the “PC xx Design Guides” (where xx designates the year) as a set of standard speci-fications to guide both hardware and software developers who are creating products that work withWindows. The requirements in these guides are part of Microsoft’s “Designed for Windows” logorequirement. In other words, if you produce either a hardware or software product and you want theofficial “Designed for Windows” logo to be on your box, your product must meet the PC xx mini-mum requirements.

Following are the documents that have been produced in this series:

■ “Hardware Design Guide for Microsoft Windows 95”

■ “Hardware Design Guide Supplement for PC 95”

■ “PC 97 Hardware Design Guide”

■ “PC 98 System Design Guide”




These documents are available for download from the PC Design Guides Web site (http://www.pcdesguide.org), as well as the Microsoft Web site (http://www.microsoft.com/whdc/hwdev/platform/pcdesign/desguide/pcguides.mspx).

These system-design guides present information for engineers who design and build personal comput-ers, expansion cards, and peripheral devices that are to be used with Windows 9x/Me, NT/2000, andXP operating systems. The requirements and recommendations in these guides form the basis for therequirements of the “Designed for Windows” logo program for hardware Microsoft sponsors.

These guides include requirements for basic (desktop and mobile) systems, workstations, and evenentertainment PCs. They also address Plug and Play device configuration and power management inPC systems; requirements for universal serial bus (USB) and IEEE-1394; and new devices supportedunder Windows, including new graphics and video device capabilities, DVD, scanners and digitalcameras, and other devices.

NoteThese guides do not mean anything directly for the end user; instead, they are meant to be guides for PC manufacturers todesign and build their systems. As such, they are guides or recommendations, and they do not have to be followed to theletter. In some ways, they are a market-control tool for Intel and Microsoft to further wield their influence over PC hardwareand software. In reality, the market often dictates that some of these recommendations are disregarded, which is one rea-son they continue to evolve with new versions year after year.

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The PC 2001 System Design Guide is the most recent comprehensive design guide produced byMicrosoft and Intel. These companies now produce individual whitepapers and other resources forthis purpose. For updated system design information, see the following Web sites:

■ The Microsoft Windows Platform Design – Overview site athttp://www.microsoft.com/whdc/hwdev/platform/default.mspx

■ The Intel developer Web site at http://developer.intel.com

System TypesPCs can be broken down into many categories. I like to break them down in two ways—by the type ofsoftware they can run and by the motherboard host bus, or processor bus design and width. Becausethis book concentrates mainly on hardware, let’s look at that first.

When a processor reads data, the data moves into the processor via the processor’s external data busconnection. The processor’s data bus is directly connected to the processor host bus on the mother-board. The processor data bus or host bus is also sometimes referred to as the local bus because it islocal to the processor that is connected directly to it. Any other devices connected to the host busessentially appear as if they are directly connected to the processor as well. If the processor has a 32-bit data bus, the motherboard must be wired to have a 32-bit processor host bus. This means the sys-tem can move 32 bits of data into or out of the processor in a single cycle.

◊◊ See “Data I/O Bus,” p. 46.

Different processors have different data bus widths, and the motherboards designed to accept themrequire a processor host bus with a matching width. Table 2.2 lists all the Intel and major Intel-compatible processors, their data bus widths, and their internal register sizes.

Table 2.2 Intel and Intel-Compatible Processors and Their Data Bus/Register Widths

Processor Data Bus Width Register Size

8088 8-bit 16-bit

8086 16-bit 16-bit

286 16-bit 16-bit

386SX 16-bit 32-bit

386DX 32-bit 32-bit

486/AMD-5x86 32-bit 32-bit

Pentium/AMD-K6 64-bit 32-bit

Pentium Pro/Celeron/II/III 64-bit 32-bit

AMD Duron/Athlon/Athlon XP 64-bit 32-bit

Pentium 4 64-bit 32-bit

Itanium 64-bit 64-bit

AMD Athlon 64 64-bit 64-bit

A common misconception arises in discussions of processor widths. Although the Pentium and newerprocessors all have 64-bit data bus widths, their internal registers are only 32 bits wide, and theyprocess 32-bit commands and instructions. The Intel Itanium and AMD Athlon 64 are the first Intel-compatible processors to have 64-bit internal registers. Thus, from a software point of view, all chipsfrom the 386 to the Athlon/Duron and Celeron/Pentium 4 have 32-bit registers and execute 32-bitinstructions. From the electronic or physical perspective, these 32-bit, software-capable processorshave been available in physical forms with 16-bit (386SX), 32-bit (386DX and 486), and 64-bit

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(Pentium and beyond) data bus widths. The data bus width is the major factor in motherboard andmemory system design because it dictates how many bits move in and out of the chip in one cycle.

◊◊ See “Internal Registers (Internal Data Bus),” p. 48.

The Itanium processor has a new Intel architecture 64-bit (IA-64) instruction set, but it can also processthe same 32-bit instructions as processors ranging from the 386 through the Pentium 4. The Athlon 64has a new x86-compatible 64-bit architecture but is designed to use 32-bit instructions written for normalIntel or compatible x86 processors as efficiently as a normal Athlon XP or comparable processor would.

◊◊ See “Processor Specifications,” p. 41.

Referring to Table 2.2, you can see that all Pentium and newer systems have a 64-bit processor bus.Pentium processors, whether they are the original Pentium, Pentium MMX, Pentium Pro, or even thePentium II/III or 4, all have 64-bit data buses, as do comparable processors from AMD (K6 family,Athlon, Duron, Athlon XP, and Athlon 64).

As you can see from Table 2.2, systems can be broken down into the following hardware categories:

■ 8-bit

■ 16-bit

■ 32-bit

■ 64-bit

What is interesting is that besides the bus width, the 16- through 64-bit systems are remarkably simi-lar in basic design and architecture. The older 8-bit systems are very different, however. This gives ustwo basic system types, or classes, of hardware:

■ 8-bit (PC/XT-class) systems

■ 16/32/64-bit (AT-class) systems

In this verbiage, PC stands for personal computer; XT stands for an extended PC; and AT stands for anadvanced-technology PC. The terms PC, XT, and AT, as they are used here, are taken from the originalIBM systems of those names. The XT was a PC system that included a hard disk for storage in additionto the floppy drives found in the basic PC system. These systems had an 8-bit 8088 processor and an 8-bit Industry Standard Architecture (ISA) bus for system expansion. The bus is the name given to expan-sion slots in which additional plug-in circuit boards can be installed. The 8-bit designation comes fromthe fact that the ISA bus found in the PC/XT class systems can send and receive only 8 bits of data in asingle cycle. The data in an 8-bit bus is sent along eight wires simultaneously, in parallel.

◊◊ See “The ISA Bus,” p. 350.

16-bit and greater systems are said to be AT-class, which indicates that they follow certain standardsand that they follow the basic design first set forth in the original IBM AT system. AT is the designa-tion IBM applied to systems that first included more advanced 16-bit (and later, 32- and 64-bit)processors and expansion slots. AT-class systems must have a processor that is compatible with Intel286 or higher processors (including the 386, 486, Pentium, Pentium Pro, Pentium II, Pentium III,Pentium 4, and Pentium M processors), and they must have a 16-bit or greater system bus. The systembus architecture is central to the AT system design, along with the basic memory architecture, inter-rupt request (IRQ), direct memory access (DMA), and I/O port address design. All AT-class systems aresimilar in the way these resources are allocated and how they function.

The first AT-class systems had a 16-bit version of the ISA bus, which is an extension of the original 8-bit ISA bus found in the PC/XT-class systems. Eventually, several expansion slot or bus designs weredeveloped for AT-class systems, including the following:

■ 16-bit ISA/AT bus

■ 16-bit PC Card (PCMCIA) bus

■ 16/32-bit Extended ISA (EISA) bus

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System Types 35

■ 16/32-bit PS/2 Micro Channel Architecture (MCA) bus

■ 32-bit VESA Local (VL) bus

■ 32/64-bit Peripheral Component Interconnect (PCI) bus

■ 32-bit CardBus (PCMCIA) bus

■ PCI Express bus

■ ExpressCard bus

■ 32-bit Accelerated Graphics Port (AGP) bus

A system with any of these types of expansion slots is by definition an AT-class system, regardless of theactual Intel or Intel-compatible processor that is used. AT-type systems with 386 or higher processorshave special capabilities not found in the first generation of 286-based ATs. These distinct capabilities arein the areas of memory addressing, memory management, and possible 32- or 64-bit wide access to data.Most systems with 386DX or higher chips also have 32-bit bus architectures to take full advantage of the32-bit data transfer capabilities of the processor.

Until recently, PC systems continued to incorporate a 16-bit ISA slot for backward-compatibility and lower-function adapters. However, in virtually all motherboards today, ISA slots have been completely replaced byPCI slots along with an AGP slot (a specialized expansion slot design) available in most systems (except for afew entry-level models with integrated video) for high-performance graphics. In addition, most portable sys-tems use PC Card (PCMCIA) and CardBus slots in the portable unit and PCI slots in optional docking stations.

Chapter 4, “Motherboards and Buses,” contains in-depth information on these and other PC system buses,including technical information such as pinouts, performance specifications, and bus operation and theory.

Table 2.3 summarizes the primary differences between the older 8-bit (PC/XT) systems and modern AT sys-tems. This information distinguishes between these systems and includes all IBM and compatible models.

Table 2.3 Differences Between PC/XT and AT Systems

System Attributes (8-Bit) PC/XT Type (16/32/64-Bit) AT Type

Supported processors All x86 or x88 286 or higher

Processor modes Real Real/Protected/Virtual Real

Software supported 16-bit only 16- or 32-bit

Bus slot width 8-bit 16/32/64-bit

Slot type ISA only ISA, EISA, MCA, PC Card, CardBus, ExpressCard, VL-Bus,PCI, PCI Express, and AGP

Hardware interrupts 8 (6 usable) 16 (11 usable)

DMA channels 4 (3 usable) 8 (7 usable)

Maximum RAM 1MB 16MB/4GB or more

Floppy controller speed 250Kbps 250/300/500/1,000 Kbps

Standard boot drive 360KB or 720KB 1.2MB/1.44MB/2.88MB

Keyboard interface Unidirectional Bidirectional

CMOS memory/clock None standard MC146818-compatible

Serial-port UART 8250B 16450/16550A or greater

The easiest way to identify a PC/XT (8-bit) system is by the 8-bit ISA expansion slots. No matter whichprocessor or other features the system has, if all the slots are 8-bit ISA, the system is a PC/XT. AT (16-bitplus) systems can be similarly identified—they have 16-bit or greater slots of any type. These can be ISA,EISA, MCA, PC Card (formerly PCMCIA), CardBus, VL-Bus, or PCI. Any system using the new high-speed

Chapter 2

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serial buses such as PCI Express or ExpressCard also qualifies as an AT-class system. Using this informa-tion, you can properly categorize virtually any system as a PC/XT type or an AT type. No PC/XT type(8-bit) systems have been manufactured for many years. Unless you are in a computer museum, virtu-ally every system you encounter today is based on the AT-type design.

System ComponentsA modern PC is both simple and complicated. It is simple in the sense that over the years, many of thecomponents used to construct a system have become integrated with other components into fewer andfewer actual parts. It is complicated in the sense that each part in a modern system performs manymore functions than did the same types of parts in older systems.

This section briefly examines all the components and peripherals in a modern PC system. Each item isdiscussed further in later chapters.

The components and peripherals necessary to assemble a basic modern PC system are listed in Table 2.4.

Table 2.4 Basic PC Components

Component Description

Motherboard The motherboard is the core of the system. It really is the PC; everything else is connected to it, and itcontrols everything in the system. Motherboards are covered in detail in Chapter 4.

Processor The processor is often thought of as the “engine” of the computer. It’s also called the CPU (central processing unit). Processors are covered in detail in Chapter 3, “Microprocessor Types and Specifications.”

Memory The system memory is often called RAM (for random access memory). This is the primary memory, which (RAM) holds all the programs and data the processor is using at a given time. Memory is discussed in Chapter 6,

“Memory.”

Case/chassis The case is the frame or chassis that houses the motherboard, power supply, disk drives, adapter cards, and any other physical components in the system. The case is covered in detail in Chapter 21, “Power Supply and Chassis/Case.”

Power supply The power supply feeds electrical power to every single part in the PC. The power supply is covered indetail in Chapter 21.

Floppy drive The floppy drive is a simple, inexpensive, low-capacity, removable-media, magnetic-storage device. Many recent systems use other types of removable magnetic or USB-based flash memory devices instead of floppydrives for removable storage. Floppy drives are covered in detail in Chapter 11, “Floppy Disk Storage,” and other removable-media drives are covered in Chapter 12, “High-Capacity Removable Storage.”

Hard drive The hard disk is the primary archival storage memory for the system. Hard disk drives are also discussedin Chapter 10, “Hard Disk Storage.”

CD or DVD CD (compact disc) and DVD (digital versatile disc) drives are relatively high-capacity, removable media, drive optical drives; many recent systems include a rewriteable CD (CD-RW) along with or combined with a

DVD-ROM drive. These drives are covered in detail in Chapter 13, “Optical Storage.”

Keyboard The keyboard is the primary device on a PC that is used by a human to communicate with and control asystem. Keyboards are covered in Chapter 18, “Input Devices.”

Mouse Although many types of pointing devices are on the market today, the first and most popular device for this purpose is the mouse. The mouse and other pointing devices are discussed in Chapter 18.

Video card* The video card controls the information you see on the monitor. Video cards are covered in detail inChapter 15, “Video Hardware.”

Monitor Monitors are covered in Chapter 15.

Sound card* It enables the PC to generate complex sounds. Sound cards and speakers are discussed in detail inChapter 16, “Audio Hardware.”

Modem* Most prebuilt PCs ship with a modem (generally an internal modem). Modems and other Internet-connectivity devices and methods are covered in Chapter 19, “Internet Connectivity.”

Components marked with an * may be integrated into the motherboard on many recent systems, particularly entry-level systems.

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