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Overview of System Components

Overview of System Components

This chapter discusses the differences in system architecture among PC-compatible systems and also explains memory structure and use. In addition, the chapter discusses how to obtain the documentation necessary for maintaining and upgrading your computer.

Types of Systems

Many types of PC-compatible systems have been on the market since the first PC. Most systems are similar, but a few important differences in system architecture are known. Operating systems such as OS/2 1.x and Windows 3.1 require at least a 286 CPU platform on which to run. OS/2 2.x, 3.x (Warp), and Windows 95 will run on a 386 system, and Windows NT 4.x requires at least a 486 CPU to run. Knowing and understanding the differences among these hardware platforms will enable you to plan, install, and use the different operating systems and applications in order for you to use the hardware optimally.

All PC-compatible systems can be broken down into two basic system types, or classes, of hardware:

  • 8-bit (PC/XT-class) systems

  • 16/32/64-bit (AT-class) systems

The term PC stands for personal computer, XT stands for an eXTended PC, and AT stands for an Advanced Technology PC. The terms PC, XT, and AT as used here are taken from the original IBM systems of those names. The XT basically was a PC system that included a hard disk for storage in addition to the floppy drive(s) 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 expansion slots in which additional plug-in circuit boards can be installed. The 8-bit designation comes from the fact that the ISA Bus found in the PC/XT class systems can send or receive only 8 bits of data in a single cycle. The data in an 8-bit bus is sent along eight wires simultaneously, in parallel.

More advanced systems are said to be AT-class, which indicates that they follow certain standards and follow the basic design first set forth in the original IBM AT system. AT is the designation 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 any processor that is compatible with Intel 286 or higher processors and must have a 16-bit or greater system bus. The system bus architecture is central to the AT system design.

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 were developed for AT-class systems, including those in the following list:

  • 16-bit ISA Bus

  • 16/32-bit PS/2 Micro Channel Architecture (MCA) Bus

  • 16/32-bit Extended ISA (EISA) Bus

  • 16-bit PC-Card (PCMCIA) Bus

  • 32-bit Cardbus (PCMCIA) Bus

  • 32-bit VESA Local (VL) Bus

  • 32/64-bit Peripheral Component Interconnect (PCI) Bus

  • Accelerated Graphics Port (AGP)

  • Universal Serial Bus (USB)

  • FireWire (IEEE 1394)

A system with any of these types of expansion slots is by definition an AT-class system, regardless of the actual Intel or Intel-compatible processor used. AT-type systems with 386 or higher processors have special capabilities not found in the first generation of 286-based ATs. The 386 and higher systems have distinct capabilities regarding 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 the 32-bit data transfer capabilities of the processor.

The 64-bit PC systems incorporate 16-bit ISA slots for backward compatibility and lower function adapters, and PCI slots for truly high performance adapters. Most portable systems use PC-Card and Cardbus slots in the portable unit, as well as ISA and PCI slots in optional docking stations.

Chapter 5 - Bus Slots and I/O Cards, contains a great deal of in-depth information on these and other PC system buses, including technical information such as pinouts, performance specifications, and bus operation and theory.

Table 2.1 summarizes the primary differences between the older 8-bit (PC/XT) systems and the newer AT system. This information distinguishes between these systems and includes all IBM and compatible models.

Table 2.1  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
Expansion slot width 8-bit 16/32/64-bit
Slot type ISA only ISA, MCA, EISA, PC-Card, Cardbus, VL-Bus, PCI, AGP, USB, FireWire
Hardware interrupts 8 (6 usable) 16 (11 usable)
DMA channels 4 (3 usable) 8 (7 usable)
Maximum RAM 1M 16M or more
Floppy controller speed 250 Kbit/sec 250/300/500/1,000 Kbit/sec
Standard boot drive 360K or 720K 1.2M/1.44M/2.88M
Keyboard interface Unidirectional Bi-directional
CMOS memory/clock None standard MC146818 compatible
Serial-port UART 8250B 16450/16550A

The easiest way to identify a PC/XT (8-bit) system would be by the 8-bit ISA expansion slots. No matter what processor or other features the system had, if all of the slots are 8-bit ISA, then the system would be a PC/XT. AT (16-bit plus) systems can be similarly identified by having 16-bit or greater slots of any type. These could be ISA, MCA, EISA, PCCard (formerly PCMCIA), Cardbus, VL-Bus, PCI, AGP, USB or FireWire. Using this information, you can properly categorize virtually any system as a PC/XT type or an AT type.

For more information on the other architectural differences between these types of systems, consult the various sections of the book that deal with each system component.


One of the biggest problems in troubleshooting, servicing, or upgrading a system is having proper documentation. Notice that good documentation is critical for system support and future upgrade capability. Because it can be a problem getting documentation on systems or components that are older, the time to acquire documentation is when the system or components are new.

There are several types of documentation available to cover a given system:

  • System-level documentation. The system-specific manual(s) put together by the system manufacturer or assembler. Some companies break this down further into Operations, Technical Reference, and Service manuals.

  • Component-level documentation. The specific OEM (Original Equipment Manufacturer) manuals for each major component such as the motherboard, video card, hard disk, floppy drive, CD-ROM drive, modem, network card, SCSI adapter, and so on.

  • Chip- and chipset-level documentation. The most specific and technical manuals which cover items such as the processor, motherboard chipset, super I/O chip, BIOS, memory modules, video chipset, and various disk controller, SCSI bus interface, network interface, and other chips used throughout the system.

The system- and component-level documentation is essential for even the most basic troubleshooting and upgrading tasks. More technical literature such as the chip- and chipset-level documentation is probably necessary only for software and hardware developers who have more special requirements. However, if you really want to know as much about a system as possible, then you will find that having the chip- and chipset-level documentation can give you insights and information about a system you simply can't get otherwise. This section will examine all of this documentation and, most importantly, explain how to get it!

Basic System Documentation

When you purchase a complete system, it should include a basic set of documentation. What you actually get will vary widely depending on what type of system you get and who put it together.

Name-brand manufacturers such as IBM, Compaq, Hewlett-Packard, Toshiba, Packard Bell, and others will almost certainly include custom manuals they have developed specifically for each system they sell. For those types of systems which use proprietary components, you should contact the manufacturer for their specific documentation.

Companies who assemble or build systems out of industry standard components may either produce their own documentation, or simply include the documentation that is included with the components they install in their systems. Most of the larger system assemblers such as Gateway, Dell, Micron, Midwest Micro, and others will also have their own custom-produced documentation for the main system unit, and may even have custom manuals for many of the individual system components.

This type of documentation is useful for people setting up a system for the first time or for performing simple upgrades, but often lacks the detailed technical reference information needed by somebody who might be troubleshooting the system or upgrading it beyond what the manufacturer or assembler had originally intended. In that case, you are better off with any of the OEM component manuals which are available directly from the component or peripheral manufacturers themselves.

Most of the smaller system assemblers will forego any custom-produced system documentation and simply include the component level manuals for the components they are including in the assembled system. For example, if an Asus motherboard and STB video card were included in a particular system, then the manuals from Asus and STB which originally came with those products would be included with the assembled system.

NOTE: Some system assemblers like to keep the component documentation and not include it with the systems they build. This forces the purchaser of the systems to go back to the assembler for any support or technical information, and also tends to make the purchaser believe that the assembler actually manufactured the system rather than simply assembled it using off-the-shelf components. It's not recommended to purchase from any system assembler who did not include all of the documentation for the individual system components they are installing.

The standard manuals included with most system components and peripherals contain basic instructions for system setup, operation, testing, relocation, and option installation. Some sort of basic diagnostics disk (sometimes called a Diagnostics and Setup or Reference Disk) normally is included with a system as well. Often the diagnostics are simply a custom labeled version of a commonly available commercial diagnostic program.

TIP: Most system vendors and equipment manufacturers have jumper settings and manuals available on their Web sites in downloadable form, which can be very useful.

Component and Peripheral Documentation

It is a well-known fact that many systems are not really manufactured as a custom unit by a single company but instead are assembled out of standard off-the-shelf components that are available on the open market. In fact, it's recommended that people purchase exactly that type of system, because all of the components conform to known standards and can easily be replaced or upgraded later.

Even proprietary manufactured systems such as IBM, Compaq, Hewlett-Packard, Packard Bell, and others use at least some off-the-shelf standard components (disk drives, for example). To fully document a system, you have to take an inventory of the standard components used, and collect all of the OEM documentation or product manuals for them.

This process is simple; when you are supporting a given system, first disassemble it and write down all of the information on each of the components inside. Sometimes you will need to do a little more investigating or even ask the company who assembled the system exactly what components they included. Most components such as hard disks, CD-ROM drives, video cards, sound cards, network cards, and more are pretty easy to identify. Somewhere on the device or card there should be a label indicating at least the manufacturer and usually also the model number. You can go to the Internet Web site of that company to obtain the complete documentation on their products.

Motherboards can be tricky to identify because not all manufacturers mark them clearly. In that case, you are best off contacting the company who sold you the computer to ask them exactly what motherboard you have. Don't be afraid to ask the company exactly what motherboard or other components they are installing in the systems they sell. If they can't or won't answer, you may be better off purchasing from a different company in the future. If the company who sold the system is no longer available or cannot help, check the paperwork that came with the system. Sometimes there are clues in the original paperwork that might indicate what motherboard your system includes.

As an example, our system is a Gateway P6 (Pentium Pro) 200MHz system which included the following industry standard components:

Motherboard: Intel VS440FX "Venus"
Video Card: STB Velocity 3D
Hard Disk: Quantum Fireball TM3840A
Floppy Drive: Panasonic JU-256
CD-ROM Drive: Mitsumi FX120

Many of the larger system assemblers like Gateway and Dell have been using Intel motherboards. A lot of motherboards use Intel processors and chipsets, but some people may not be aware that Intel makes complete PC motherboards as well. Even so, Gateway did not include the actual Intel motherboard or other component manuals but instead included their own custom manuals for the motherboard, video card, hard disk, and CD-ROM drive. In this case you have to contact the individual companies directly over the Internet or via the telephone, to be able to obtain more detailed documentation on all of these products. Many times the OEM documentation or product manuals can be downloaded directly from the respective companies' Web sites, often in the form of Adobe Acrobat .PDF files, which you can read with the Adobe Acrobat Reader.

NOTE: Not all of these manuals are available online, and even if they are, it is still nice to have the printed manuals or datasheets in your documentation library for future reference.

Chip and Chipset Documentation

If you really want the ultimate in documentation for your system, it's highly recommended getting the documentation for the various chips and chipsets in your system. This would include specific manuals for each of the major chip-level components in the system--such as the processor, motherboard chipset, BIOS, super I/O chipset, and so on. Before you can get this documentation, you must first identify all of the relevant chips and chipsets in your system.

The process is relatively simple. Look at the documentation for each major component, especially the motherboard. The OEM motherboard documentation should tell you which chipset is used on the board, which processors are supported, and which super I/O chip is used. From the OEM documentation you have on your system components, you should be able to find out what the following major chip and chipsets are:

Motherboard Chipset
Super I/O Chip
Video Chipset

If your motherboard has an integrated video card, then the video chipset type will be listed there also. If you have a separate video card, then look in the video card manual and it should clearly identify the video chipset used.

The most important chips you will want to identify are on the motherboard. The first thing you would want to identify is the processor. This should be relatively easy; most PC systems use Intel processors. A small percentage of systems use AMD or Cyrix processors, or versions of these processors sold under other names. The documentation that comes with the system will normally identify which brand of processor you have, and which model and speed it is.

If you aren't sure what processor is in the system, software programs such as the MSD (Microsoft Diagnostics) program are included with Windows, or a system diagnostic you purchase such as the Norton Utilities.

Normally the processor is the largest chip on the motherboard, and can often be identified by simply reading the information stamped on it. In some cases, the processor will have a heat sink or fan attached to the top, in which case you may have to either remove the heat sink or fan to read the information stamped on top of the chip, or simply remove the entire processor and heat sink or fan assembly to read the information stamped on the bottom of the chip.

The chipset is difficult for software to determine, so you will either have to find out which chipset you have from the motherboard documentation or by first-hand inspection. The motherboard chipset normally consists of several large chips on the board; there are chipsets that use anywhere from one to six chips. Generally each chip in the set will have a part number stamped on it, but the chipset itself will be named after the main chip. The mentioned Pentium Pro board had two chips labeled 82441FX and 82442FX; these are both a part of what Intel calls the 440FX chipset.

Finding out the manufacturer of the motherboard BIOS is easy; that is normally found in the motherboard manual. It is also displayed, along with the exact version number you have, every time you power the system on. Most systems use an AMI, Award, or Phoenix BIOS, but there are several other manufacturers as well.

Virtually all motherboards built in the '90s and later include a special interface chip called a super I/O chip. This is a single chip device that normally includes the following components:

  • Primary and secondary IDE host adapters

  • Floppy controller

  • Two serial ports

  • One parallel port

Some do not include the IDE host adapters, such as the National Semiconductor 87308 used in the mentioned Pentium Pro motherboard. That particular chip also includes an 8042-style keyboard controller and a MC146818-style real-time clock with nonvolatile CMOS RAM. Other super I/O chips may include a game (joystick) interface as well. Obtaining the documentation for your particular super I/O chip will of course tell you exactly what it's capabilities are.

Another important chipset in a system is the video chipset. This is normally found on the video card, or on the motherboard if the motherboard has built-in video. The OEM video card or motherboard documentation should tell you exactly which video chipset you have. If not, then you can use free software such as MSD or commercial programs such as Norton Utilities to identify which chipset you have without even opening up the case. A last resort would be to open the system and read the part number right off of the video chipset, which is usually the largest chip on the video card.

Using a Pentium Pro 200MHz system as an example, in this case it contained the following main chip and chipset components:

Processor: Intel Pentium Pro
Motherboard Chipset: Intel 440FX "Natoma"
Super I/O Chip: National Semiconductor PC87308
Video Chipset: S3 Inc. ViRGE/VX

Note that this particular motherboard did not have the video integrated, so the video chipset was on the video card.

From this documentation, you can learn about the capability to increase the clock multiplier setting on the motherboard to an otherwise undocumented 3.5x, which results in running the Pentium Pro 200 chip at 233MHz! You are also able to get more information on the various serial, parallel, and disk controllers contained in the super I/O chip, and learn more about the advanced CMOS settings in the BIOS Setup routines.

For example, many people have questions about the Advanced CMOS settings. Most people assume that these settings would be described in their ROM BIOS documentation because the ROM-based CMOS Setup program in their system controls these settings. If you contact the BIOS manufacturer or read the BIOS documentation, you will quickly find out that the ROM BIOS manufacturer knows little or nothing about these settings. In fact, these settings actually have little or nothing to do with the particular ROM BIOS used, and everything to do with the particular motherboard chipset used. You can find descriptions of all these settings in the documentation for your motherboard chipset, which can be obtained from the chipset manufacturer.

Manufacturer-Specific Documentation

If your system is from a name-brand manufacturer--such as IBM, Compaq, Hewlett-Packard, Toshiba, and others--then there may be a wealth of information available in manufacturer-specific manuals and documentation. Because of the specific nature of the information in these types of manuals, you most likely will have to obtain it from the manufacturer of the system.

The process of obtaining other manufacturers' manuals may (or may not) be easy. Most large companies run responsible service and support operations that provide technical documentation. Other companies either do not have or are unwilling to part with such documentation, in an effort to protect their service departments (and their dealers' service departments) from competition. Contact the manufacturer directly; the manufacturer can direct you to the correct department so that you can inquire about this information.

Warranties and Service Contracts

With the increasing competition among hardware vendors, a good warranty is one way for a specific manufacturer to stand out from the crowd. Although most companies offer a one-year warranty on their systems, others offer longer warranty periods, such as three years or more.

In addition to extended-length warranties, some manufacturers offer free or nearly free on-site service during the warranty period.

TIP: Most companies offer extended-length warranties and free or low-cost on-site service. If your system is "mission-critical," meaning it absolutely must be functioning all the time (such as with a network file, database, or application server), you might want to consider an on-site service contract. Such contracts are usually overkill for a standard PC.

The high prices of service contracts also might affect the quality of service you receive. Technicians could try to make their work seem more complex than it actually is to make you believe that the contract's price is justified. For example, a service technician might replace your hard disk or entire motherboard with a spare when all you need is low-level formatting for the hard disk or a simple fix for the motherboard such as a single memory chip. A "defective" drive, for example, probably is just returned to the shop for low-level formatting. Eventually, it ends up in somebody else's system. Replacing a part is faster and leaves the impression that your expensive service contract is worth the price because you get a "new" part. You might be much less impressed with your expensive service contract if the service people visit, do a simple troubleshooting procedure, and then replace a single cable or spend 15 minutes reformatting the hard disk. With some basic troubleshooting skills, simple tools, and a few spare parts, you can eliminate the need for most of these expensive service contracts.

TIP: If you have many systems, you can justify carrying a spare-parts inventory, which can also eliminate the need for a service contract. For less than what a service contract costs for five to 10 systems, you often can buy a complete spare system each year. Protecting yourself with extra equipment rather than service contracts is practical if you have more than 10 computers of the same make or model. For extremely time-sensitive applications, you might be wise to buy a second system along with the primary unit--such as in a network file-server application. Only you can make the appropriate cost-justification analysis to decide whether you need a service contract or a spare system.

In some instances, buying a service contract can be justified and beneficial. If you have a system that must function at all times and is so expensive that you cannot buy a complete spare system, or for a system in a remote location far away from a centralized service operation, you might be wise to invest in a good service contract that provides timely repairs. Before contracting for service, you should consider your options carefully. These sources either supply or authorize service contracts:

  • Manufacturers

  • Dealers or vendors

  • Third parties

Although most users take the manufacturer or dealer service, sometimes a third party tries harder to close the deal; for example, it sometimes includes all the equipment installed, even aftermarket items the dealers or manufacturers don't offer. In other cases, a manufacturer might not have its own service organization; instead, it makes a deal with a major third-party nationwide service company to provide authorized service.

After you select an organization, several levels of service often are available. Starting with the most expensive, these levels of service typically include:

  • Four-hour on-site response

  • Next-day on-site response

  • Carry-in/ship-in or "depot" service

The actual menu varies from manufacturer to manufacturer. For example, some manufacturers offer only a full 24-hours-a-day, 7-days-a-week, on-site service contract. It is also possible that older systems are not included in such a service contract, or only carry-in service is available for older systems.

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