The Motherboard

The motherboard represents the logical foundation of the computer. In other words, everything that makes a computer a computer must be attached to the motherboard. From the CPU to storage devices, from RAM to printer ports, the motherboard provides the connections that help them work together.

The CD included with this book contains important Study Lab material for this chapter, as well as Chapters 222 in this book. The Study Lab for each chapter contains terms to study, exercises, and practice testsall in printable PDF format (Adobe Acrobat Reader is included on the CD, too). These Study Lab materials will help you gear up for the A+ Exam. Also, the CD includes an industry-leading test engine from PrepLogic, which simulates the actual A+ test so that you can be sure that you're ready when test day arrives. Don't let the A+ test intimidate you. If you've read the chapters, worked through the Study Lab, and passed the practice tests from PrepLogic, you should be well prepared to ace the test!

Also, you'll notice that some words throughout each chapter are in bold format. These are study terms that are defined in the Study Lab. Be sure to consult the Study Lab when you are finished with this chapter to test what you've learned.

Take a close look at a motherboard, and you'll see fine copper -colored wire traces on the top and bottom that run between different parts of the motherboard. These wire traces are portions of the motherboard's bus structure. In a city, a bus takes passengers from one point to another; in a computer, a bus carries signals from one component to another.

The motherboard is essential to computer operation in large part because of the two major buses it contains: the system bus and the I/O bus . Together, these buses carry all the information between the different parts of the computer.

The System Bus

The system bus carries four different types of signals throughout the computer:

• Data

• Power

• Control

• Address

To help you understand this concept, let's take an imaginary trip to Chicago and compare the city to a typical motherboard. If you were on the Sears Tower observation deck overlooking downtown Chicago one evening, you would first notice the endless stream of cars , trucks , and trains carrying people and goods from everywhere to everywhere else along well-defined surface routes (the expressways and tollways, commuter railroads, Amtrak, and airports). You can compare these routes to the data bus portion of the system bus, which carries information between RAM and the CPU. If you've ever listened to a station such as Chicago's WBBM (760AM), you've heard how traffic slows down when expressway lanes are blocked by construction or stalled traffic. In your computer, wider data buses that enable more " lanes " of data to flow at the same time promote faster system performance.

Now, imagine that you've descended to street level, and you've met with a local utility worker for a tour of " underground Chicago." On your tour, you will find an elaborate network of electric and gas lines beneath the street carrying the energy needed to power the city. You can compare these to the power lines in the system bus, which transfer power from the motherboard's connection to the power supply to the integrated circuits ( ICs or chips ) and expansion boards connected to the motherboard.

Go back to street level, and notice the traffic lights used both on city streets and on the entrance ramps to busy expressways, such as the Eisenhower and the Dan Ryan. Traffic stops and starts in response to the signals. Look at the elevated trains or at the Metra commuter trains and Amtrak intercity trains; they also move as directed by signal lights. These signals, which control the movement of road and rail traffic, can be compared to the control lines in the system bus, which control the transmission and movement of information between devices connected to the motherboard.

Finally,as you look around downtown, take a close look at the men and women toting blue bags around their shoulders or driving electric vans and Jeeps around the city. As these mail carriers deliver parcels and letters , they must verify the correct street and suite addresses for the mail they deliver. They correspond to the address bus, which is used to "pick up" information from the correct memory location among the megabytes of RAM in computer systems and "deliver" new programs and changes back to the correct memory locations.

The I/O bus connects storage devices to the system bus and can be compared to the daily flow of commuters and travelers into the city in the morning, and out again in the evening.

Between them, the system and I/O buses carry every signal throughout the motherboard and to every component connected to the motherboard.

Essential System Components Found on the Motherboard

Because the motherboard contains the system and I/O buses, it isn't surprising that the most central components to computing are found attached to the motherboard, as listed in Table 4.1.

Table 4.1. Components Located on All Motherboards

Component	Use	How Attached to Motherboard	Notes
CPU	Computational " brains " of computer	Dedicated socket or slot [1]	A few CPUs are soldered in place
RAM (random access memory)	Programs are loaded into this for operation; data resides here until saved to storage device	Dedicated sockets and/or soldered	RAM can be upgraded to limits determined by CPU type and motherboard design
ROM (read-only memory)	Firmware containing drivers for standard devices; power-on self-test	Dedicated socket	Most common ROM is the ROM BIOS
Keyboard connector	Attach keyboard	Soldered	Can be damaged by careless insertion/removal of keyboard cable
CMOS/RTC chip [2]	Records BIOS settings; keeps date and time	Soldered	Some contain their own battery
Battery [2]	Maintains contents of CMOS/RTC chip	Soldered, socketed, or cabled	Many different types on older systems
Cache RAM	Holds a copy of last memory locations read for faster performance	Dedicated socket or surface mounted	Introduced with 386-based systems; common with 486 and Pentium; Pentium II and newer processors include all cache RAM inside the CPU
Expansion slots	Enables expansion of computer's capabilities with new ports and so forth	Soldered in place	ISA, VL-Bus, EISA, MCA, PCI, and AGP types
Chipset	A set of chips (usually two) on the motherboard that replace many individual chips	Soldered in place	Most motherboards use a chipset that includes a North Bridge chip with a high-speed interface to memory and a South Bridge chip with interfacing to ATA and USB ports, PCI and ISA buses, and Super I/O chip and BIOS chip
Super I/O chip	Chip that replaces serial, parallel, and keyboard controller chips; connects with BIOS chip on some systems	Soldered in place	Might be integrated into the South Bridge chip on some recent chipsets
BIOS chip	Chip that contains setup options and POST (power-on self-test) for system	Soldered in place or socketed	Connect to the Super I/O chip or South Bridge chip

^[1] "Dedicated" means that the socket or slot can only be used for the device listed .

^[2] This component is found in all PCs using an Intel 286class CPU or above but is rarely found in PCs using an 8088 or 8086 CPU . Most of these computers used switches to set configuration options and didn't have built-in RTC (real-time clocks) .

Until the mid-1990s, components such as hard drive and floppy drive controllers, sound cards, network cards, and serial and parallel ports were added to typical systems through the use of add-on cards.

Integrated Motherboard Ports

During the first decade or so of the PC era, if you wanted to add a port, you added a card. To avoid using up all the expansion slots, some companies developed multi-I/O cards, which combined serial, parallel, and other ports on a single card. However, from the mid-1990s to the present, motherboards have included more and more ports and expansion connections that formerly required add-on cards. Ports added to the motherboard are often referred to as integrated ports .

Table 4.2 lists components that are included in recent motherboard designs.

Table 4.2. Components Found on Recent and Current Motherboards

Component	Use	Form Factor	Notes
ATA/IDE interface	Runs ATA/IDE and ATAPI storage devices (hard drives, optical drives, and removable-media drives )	40-pin connector (two rows of 20)	Most recent systems feature two; each interface supports two drives.
Floppy	Runs floppy-interface storage devices	34-pin connector (two rows of 17)	Older systems can support two drives with the single interface; some newer systems support only one drive.
PS/2 mouse port	Connector for PS/2 mouse	Mini-DIN 6-pin connector	Most systems with this port also have a PS/2 keyboard port.
COM (serial) port	Connector for serial devices	DB-9 male (DB-25 male is obsolete, but can be converted to DB-9)	Systems might feature one or two.
LPT (parallel) port	Connector for parallel devices	DB-25 female	Most systems feature one.
USB (Universal Serial Bus) port	Connector for USB devices and hubs	USB Type A connector	Four or more are typical on desktop systems. Some systems have a mix of USB 1.1 and USB 2.0 (Hi-Speed USB) ports.
XGA video	Connector for VGA-class monitors	DB-15 female	Some systems with integrated graphics also feature an AGP port.
Audio	Speaker and microphone connection for WAV and MIDI playback and WAV recording	Mini- jacks for microphone and speakers	Some systems offer 4-channel or 6-channel sound.
IEEE-1394 (FireWire) port	Connector for DV camcorders and high-speed drives and scanners	6-pin or 4-pin IEEE-1394 connector	One to three might be found, primarily in legacy-free systems.

Why integrated ports? They provide clear benefits to both users and technicians setting up a system. For users, integrated ports provide lower system purchase prices, faster component performance, centralized control of components through the ROM BIOS and CMOS, and an interior less crowded with add-on cards. In other words, you might have a slot or two available in a brand-new system for future upgrades.

For technicians, the major benefits of integrated components are during initial setup: Fewer components need to be installed to bring a system to meet standard requirements and components can be enabled or disabled through the BIOS setup program. Very handy!

However, when systems must be repaired or upgraded, integrated components can be troublesome . If an integrated component fails, you must either replace the motherboard or disable the component in question (if possible) and replace it with an add-on card. Check out Figures 4.1 and 4.2 to see the locations of these components on typical Baby-AT and ATX motherboards. Note that although Baby-AT motherboards and ATX motherboards both feature a large number of built-in ports, ATX motherboards have a cluster of ports built into the rear of the motherboard and Baby-AT motherboards must use clumsy header cables to route external ports to the rear of the case.

Figure 4.1. Major components on a typical Baby-AT motherboard with integrated ports. Header cables are used to route serial, parallel, PS/2 mouse, and USB ports (if present) to the rear of the system.

Figure 4.2. Major components on a typical ATX motherboard. All ATX motherboards have a cluster of I/O ports (serial, parallel, PS/2 mouse and keyboard, USB, and others) at the rear of the motherboard.

Recognizing Expansion Slot Types

What components are fastest inside your PC? In order of speed, the CPU accesses cache memory at the fastest speed, followed by main memory, and then cards mounted in expansion slots.

tip

The A+ Certification Exam, as well as your day-to-day work, tests your ability to recognize the different expansion slot types and be able to choose the most appropriate slot for a given type of card.

Most systems have mixtures of two or more of the slot types discussed in the following sections.

Table 4.3 compares expansion slot designs by speed, data bus width, and suggested uses; you must know the speed and bus width of these slots for the exam. Most systems today primarily have PCI expansion slots, but one or two ISA slots are found on some older systems still in use. Most modern systems include either an AGP slot and/or video built into the motherboard chipset.

Table 4.3. Technical Information About Expansion Slot Types

Slot Type	Bus Width	Slot Speed	Status	Suggested Uses
ISA	8-bit, 16-bit	Approximately 8MHz	Obsolete	Modems, serial and parallel ports
EISA	32-bit	Approximately 8MHz	Obsolete	Server-optimized network interface cards (NICs), all ISA cards
VL-Bus	32-bit	2533MHz [1]	Obsolete	Video, IDE hard disk, all ISA cards
PCI	32-bit, 64-bit [2]	2533MHz, 66MHz	Current	Video, network, SCSI, sound card
AGP	32-bit	66MHz [3]	Current	Video

^[1] Runs at full speed of 486SX/DX processors (2533MHz); runs at bus speed of 486DX2/SX2/DX4 processors (2533MHz) .

^[2] 64-bit and 66MHz versions found mostly on network servers and high-performance workstations .

^[3] All versions of AGP have the same clock speed, but AGP 1x performs one transfer per clock cycle. AGP 2x, 4x, and 8x perform 2, 4, or 8 transfers per clock cycle, increasing throughput accordingly .

If ISA, PCI, and AGP are just abbreviations to you, read on to learn more.

ISA

The oldest slot type is ISA (Industry Standard Architecture ). ISA slots come in two forms: a slot with a single long connector, which can send or receive 8 bits of data, and a 16-bit or AT-style slot, which adds a shorter connection in line with the original connector. This 8-bit slot was developed for the IBM PC in 1981; the 16-bit or AT-style slot adds a shorter connector to the first one. It sends or receives 16 bits of data per operation and was developed for the IBM AT in 1984(!).

Although a few older systems still contain one or two ISA slots, the ISA slot is now considered obsolete for all except industrial computing uses. Many systems that contain ISA slots have at least one that's called a shared slota pair of tightly spaced slots that shareor a single slot cover at the back in the case. One slot or the other, but not both, can be used. Refer to Figure 4.3 to see a typical ISA slot compared to a PCI slot.

Figure 4.3. An ISA slot (top) and a PCI slot (bottom) in a shared or combo configuration. Only one of the slots can be used at a time.

Obsolete variations on ISA include EISA and VL-Bus. Both were 32-bit versions of the ISA but have been obsolete for many years .

PCI

Starting in 19931994, the PCI (Peripheral Component Interconnect ) slot rapidly replaced VL-Bus slots (a 32-bit version of the ISA slot) in both late-model 486-based machines and in most Pentium-class computers. Most computers today have PCI slots and an AGP slot, or PCI slots only. Figure 4.3 compares the most common type of PCI slot, the 33MHz, 32-bit version to a 16-bit ISA slot.

The combo or shared slot design shown in Figure 4.3 uses one slot cover at the rear of the system. You can choose whether you want to use the slower ISA slot or the faster PCI slot. Combo slot designs are common among the last generation of computers to feature ISA slots, meaning you won't see these on most newer PCs.

AGP

The PCI slot is a whole lot faster than the ISA slot, but with more and more devices using this slot, video performance began to suffer. Intel developed the Accelerated Graphics Port , or AGP slot, in 1996 strictly for high-speed video: You can't use AGP slots for anything but video. Although low-cost desktop systems and servers might use integrated video along with or instead of an AGP slot, most midrange and high-end desktop systems now feature some type of AGP slot. As Table 4.3 indicates, even the first-generation AGP slot, AGP 1x, was twice as fast as a typical PCI slot. All types of AGP slots can temporarily " borrow " system memory when creating 3D textures.

There are several variations on the AGP slot in use, depending upon the age of the system and the intended use of the system, as shown in Figure 4.4.

Figure 4.4. PCI slots compared to an AGP 1x/2x slot (top), an AGP 4x/8x slot (middle) and an AGP Pro/Universal slot (bottom).

Note that the AGP 1x/2x and AGP 4x/8x slots have their keys in different positions . This prevents installing the wrong type of AGP card into the slot. AGP 1x/2x cards use 3.3V, whereas most AGP 4x cards use 1.5V. AGP 8x cards use 0.8 or 1.5V. The AGP Pro/Universal slot is longer than a normal AGP slot to support the greater electrical requirements of AGP Pro cards (which are used in technical workstations). The protective cover over a part of the slot is intended to prevent normal AGP cards from being inserted into the wrong part of the slot. The slot is referred to as a universal slot because it supports both 3.3V and 1.5V AGP cards.

caution

Note that an AGP Pro slot cover might be removed after a system has been in service for awhile, even if an AGP Pro card wasn't inserted in a computer. If you see an AGP Pro slot without a cover and you're preparing to install an AGP card, cover the extension with a sticker to prevent damaging a standard AGP card by inserting it improperly.

Figure 4.5 shows how typical AGP, PCI, and ISA cards compare to each other. Note that the components of AGP and PCI cards are on the opposite side from the components on ISA cards.

Figure 4.5. A typical PCI graphics card (top left) compared to a typical ISA network card (top right) and a typical AGP graphics card with a Universal connector (bottom).

Motherboard Types

There are several basic motherboard designs:

• Baby-AT

• LPX

• ATX family (ATX, Micro-ATX, Flex-ATX, Mini-ITX)

• NLX

The most common of these in recent systems include the ATX family and the NLX . The others ( Baby- AT and LPX ) are found primarily in older systems that are obsolete but might still be in service on a desktop near you.

The following tables and accompanying illustrations indicate the major differences between the different motherboard types.

ATX Motherboards Compared to Other Models

The ATX family of motherboards was introduced in 1996, and has since become the dominant choice for all types of desktop computers. Odds are good that most computers you've used since the late 1990s have motherboards that belong to the ATX family. The full- size ATX and Micro-ATX motherboard designs have replaced the Baby-AT motherboard designs in full-size and mid-size tower systems, whereas the NLX and Flex-ATX motherboard designs have replaced the LPX in slimline and small form-factor corporate desktop computers.

tip

As you maintain, troubleshoot, and upgrade systems, you must be able to recognize each of these motherboard types. Recognizing different motherboard types will enable you to determine whether

• The computer uses a standard motherboard and can be upgraded by changing its motherboard

• The computer uses a proprietary motherboard that cannot be interchanged

Figure 4.6 compares the layouts of these motherboards to each other.

Figure 4.6. Baby-AT and ATX-family motherboards (top) compared to LPX and NLX motherboards (bottom).

The major distinguishing factors of each motherboard design can be summarized thus:

• Baby-AT models have expansion slots, which run parallel to the long edge of the motherboard. Built-in mouse, serial, parallel, and USB ports (if present) require header cables to be run between the ports on the motherboard and the rear of the case. Most Baby-AT motherboards use a 12-pin power connector.

  

  The Mini-ITX design created by VIA Technologies is similar to a Flex-ATX motherboard, but VIA's own C3 or Eden processors are built into the motherboard instead of being removable.

  
  

• ATX-family motherboards have expansion slots that run parallel to the short edge of the motherboard. They have a two-row cluster of ports on the rear of the motherboard (see Figure 4.7). ATX motherboards use a 20-pin power connector.

  Figure 4.7. Typical ATX (top), NLX (middle), and LPX (bottom) port configurations. Some motherboards might vary from these examples.

  

• LPX motherboards have a proprietary riser card running from the middle of the motherboard. Some use a vertical riser card as shown in Figure 4.6, in which add-on cards are parallel to the motherboard, whereas others use a T-shaped riser card in which add-on cards are at the normal 90-degree angle to the motherboard. LPX motherboards have a single row of built-in ports along the rear edge of the motherboard. LPX motherboards use the same power connector as Baby-AT motherboards.

• NLX motherboards also use a riser card, but the motherboard connects to the riser card along the right edge (as viewed from the front). NLX motherboards have a two-row cluster of ports along the rear edge of the motherboard. NLX motherboards are powered by the riser card connector.

See Chapter 5, "Power Supplies and Circuit Testing," for details about the differences in power supplies and connectors.

Figure 4.7 compares typical built-in port configurations found on the rear of ATX-family, LPX, and NLX motherboards.

Note that ATX and NLX port arrangements are similar (both have two rows), whereas the LPX ports are arranged in a single row. Keep in mind that there are lots of variations in the ports built into different systems.

Upgrade Options for Different Types of Motherboards

ATX-family motherboard upgrades, particularly for systems using ATX or Micro-ATX motherboards, are plentiful. Baby-AT motherboards and systems are obsolete, and the only motherboards available are old designs that don't support current processor and memory module types. Because of differences in riser card location and design, LPX-based systems generally cannot be upgraded with new motherboards. NLX systems are designed for fast motherboard exchanges (they use a standardized riser card), but very few third-party NLX motherboards are available. They've been used primarily by vendors manufacturing corporate-class workstations instead of upgradeable PCs.

Motherboard Installation and Removal

What keeps a motherboard from sliding around inside the case? Most ATX-family motherboards are held in place by screws that are fastened to brass spacers. Baby-AT motherboards use a combination of brass spacers and screws along with plastic stand-off spacers.

If you look at an unmounted motherboard from the top, you can see that motherboards have several holes around the edges and one or two holes toward the middle of the motherboard. When a Baby-AT motherboard is installed in a computer, you'll see that one or two of the holes have a screw in them that attaches to a brass spacer, which itself is attached to the bottom or side of the case. The remainder of the holes have the top of a plastic spacer inserted in them; the bottom of the spaces fits into a teardrop-shaped mounting hole on the bottom or side of the computer case. ATX-family motherboards, on the other hand, usually are attached to brass spacers either built into the case or a removable motherboard tray.

Before you start working with motherboards or other static-sensitive parts, see "Electro-Static Discharge (ESD)," p. 418 , for ESD and other precautions you should follow.

Step-by-Step Motherboard Removal (ATX and Baby-AT)

Removing the motherboard is an important task for the computer technician. For safety's sake, you should remove the motherboard before you install a processor upgrade as well as if you need to perform a motherboard upgrade.

To remove ATX or Baby-AT motherboards from standard cases, follow these steps:

1. Disconnect all external and internal cables attached to add-on cards after labeling them for easy reconnection.

   tip

   

   Understanding this procedure can help you both in your day-to-day work and in the A+ Certification Core Hardware Exam.

2. Disconnect all ribbon cables attached to built-in ports on the motherboard (I/O, storage, and so on) after labeling them for easy reconnection.

3. Disconnect all cables leading to internal speakers, key locks, speed switches, and other front-panel cables after labeling them for easy reconnection. All these cables must be removed before the motherboard can be removed. Marking them enables you to properly attach them to the new motherboard (see Figure 4.8).

   Figure 4.8. Front-panel cables attached to a typical motherboard, which control the case speaker, drive and power lights, and so on.

   

   tip

   

   You can purchase premade labels for common types of cables, but if these are not available, you can use blank address labels.

4. Remove all add-on cards and place them on an antistatic mat or in (not on top of) antistatic bags.

   

   See "Electro-Static Discharge (ESD)," p. 418 , for details about ESD precautions.

   
   

5. Disconnect the power-supply leads from the motherboard. The new motherboard must use the same power-supply connections as the current motherboard.

   

   See "Power Supplies and Circuit Testing," p. 149 , for details about power supply connections.

   
   

   Unscrew the motherboard mounting screws and store for reuse; verify that all screws have been removed.

   caution

   

   Easy does it with the screwdriver! Whether you're removing screws or putting them back in, skip the electric model and do it the old-fashioned way to avoid damaging the motherboard. If your motherboard is held in place with hex screws, use a hex driver instead of a screwdriver to be even more careful.

6. Remove the heatsink and the processor before you remove the motherboard and place them on an antistatic mat. Removing these items before you remove the motherboard helps prevent excessive flexing of the motherboard and makes it easier to slip the motherboard out of the case. However, skip this step if the heatsink requires a lot of downward pressure to remove and if the motherboard is not well supported around the heatsink/processor area.

If your motherboard uses plastic spacers, follow this additional step:

7. Gently push the motherboard toward the front of the case (for desktop units) or toward the bottom of the case (for tower units) to release the plastic stand-off spacers from the mounting grooves , as shown in Figure 4.9. To release the motherboard from the case, remove the screws, and then push the motherboard to release the plastic stand-off spacers from the teardrop-shaped mounting holes.

   Figure 4.9. Most Baby-AT motherboards are held in place by plastic stand-off spacers.

   

   For all types of motherboards, continue with this step:

8. Lift the motherboard and plastic stand-off spacers out of the case and place on an antistatic mat. If the motherboard is an ATX or Mini-ITX type, remove the I/O shield (the metal plate on the rear of the system that has cut-outs for the built-in ports) and store it with the old motherboard. If the motherboard is a Baby-AT type, remove the external connectors for serial, parallel, and other ports from the case and store with the old motherboard. Sometimes they will be attached to punch-outs in the case; more often, they are attached to slot covers. Use the appropriate- sized hex driver or screwdriver to remove them.

9. If you are planning to install a replacement motherboard, use a pair of pliers to squeeze together the tops of the plastic spacers in the old motherboard. Then, push them from the top until they fall out of the motherboard. They can be inserted into the new motherboard. These spacers come in different heights for use with different types of cases.

Motherboard Removal (NLX)

NLX motherboards are designed for fast, easy removal. Follow this procedure:

1. Disconnect cables from any installed add-on cards as described earlier.

2. Remove any add-on cards, remembering to handle the cards by their edges.

3. Pull the motherboard release lever to disconnect the motherboard from the NLX riser.

4. Slide the motherboard out of the case.

Preparing the Motherboard for Installation (All Types)

Before you install the new motherboard into the computer, perform the following steps:

1. Install the desired amount of memory. See Chapter 7, "RAM," for details.

2. Install the processor (CPU) and heatsink as described later in this chapter.

3. Configure CPU speed, multiplier , type, and voltage settings on the motherboard if the motherboard uses jumpers or DIP (Dual Inline Pin) switches. Note that many recent motherboards use BIOS configuration options instead.

To learn more about configuring the motherboard for a particular CPU, see "The CPU" later in this chapter.

Making these changes after the motherboard is installed in the computer is normally very difficult.

Step-by-Step Motherboard Installation (ATX/Baby-AT)

After you have prepared the motherboard for installation, follow these steps to install the motherboard:

1. Place the new motherboard over the old motherboard to determine which mounting holes should be used for standoffs (if needed) and which should be used for brass spacers. Matching the motherboards helps you determine that the new motherboard will fit correctly in the system.

2. Move brass spacers as needed to accommodate the mounting holes in the motherboard. If your case uses plastic stand-off spacers, remove them from the old motherboard and push them through the bottom of the appropriate holes on the new motherboard (as described earlier in this chapter). The spacers prevent the motherboard from shorting out on the bottom of the case.

3. If the motherboard is ATX, place the I/O shield and connector at the back of the case. Line up the mounting holes on these motherboards with the brass spacers.

   If the motherboard is a Baby-AT, place the new motherboard into the case, and make sure the plastic stand-off spacers (if used) are lined up in the correct teardrop-shaped mounting grooves at the bottom or sides of the case.

4. Gently push a Baby-AT motherboard into place until the plastic stand-off spacers snap into the mounting grooves (if present). Make sure the board is level and parallel with the side or bottom of the case. Avoid flexing the motherboard; excessive flex can damage the system or I/O bus wires and destroy the motherboard.

5. If the motherboard uses an I/O shield, make sure it is correctly positioned at the rear of the case. The I/O shield is marked to help you determine the port types on the rear of the motherboard. If the port cut-outs on some I/O shields are not completely removed, remove them before you install the shield.

6. Determine which holes in the motherboard have brass stand-off spacers beneath them and secure the motherboard using the screws removed from the old motherboard (see Figure 4.10).

   Figure 4.10. An ATX I/O shield and motherboard during installation.

   

7. Reattach the wires to the speaker, reset switch, IDE host adapter, and power lights.

8. With a Baby-AT motherboard, attach the new ribbon cables supplied with the motherboard's I/O ports if present (these might be called header cables in the documentation that came with your Baby-AT motherboard). These are normally attached to slot covers, but if your case has punch-outs for these ports, knock out the holes, remove the ports from the slot covers, and attach them to the case. This will prevent the loss of usable slots.

9. Reattach the ribbon cables from the drives to the motherboard's IDE and floppy disk drive interfaces. Match the ribbon cable's colored side to pin 1 on the interfaces.

10. Reattach the power supply connectors to the motherboard.

11. Insert the add-on cards you removed from the old motherboard; make sure your existing cards don't duplicate any features found on the new motherboard (such as sound, ATA/IDE host adapters, and so on). If they do, and you want to continue to use the card, you must disable the corresponding feature on the motherboard.

12. Attach any cables used by front-mounted ports such as USB, serial, or IEEE-1394 ports to the motherboard and case.

Step-by-Step Motherboard Installation (NLX)

After you have prepared the motherboard for installation, follow these steps to install the motherboard:

1. Line up the replacement motherboard with the motherboard rails located at the bottom of the case.

2. Slowly push the motherboard into place. After the motherboard is connected to the riser card, it stops moving.

3. Lift and push the motherboard release lever to lock the motherboard into place.

4. Replace the side panel. If the side panel cannot be replaced properly, the motherboard is not installed properly.

Case Selection and Replacement

Planning a major system upgrade? Building a computer from scratch? Helping to select a system to buy? Better think about choosing the right computer case (also called an enclosure or chassis ) for the job.

Selecting the right case for a desktop computer is important if you

• Need to build a new PC from the ground up

• Provide input for the purchase of prebuilt systems

• Upgrade a system by moving components into a new case

There are three major types of cases used in typical systems:

• Tower cases

• Desktop cases

• Slimline cases

Figure 4.11 compares the layouts of typical mid-tower, micro-tower, convertible desktop/tower, and Slimline/small form-factor cases.

Figure 4.11. Typical tower (top) and desktop (bottom) case form factors compared to each other.

There are more differences between these case types than Figure 4.11 shows: For the gory details, read on!

Tower Cases

Tower cases get their name from their layout: The case stands upright on the short side.

Current mini-, mid-, and full-tower cases are designed to work with all types of ATX and Mini-ITX motherboards and ATX power supplies; older models are designed for Baby-AT motherboards and LPX power supplies. They differ in the number of 3.5-inch and 5.25-inch drive bays available. Generally, cases in these categories have five or more total drive bays and provide the greatest flexibility in system design and component choice.

How can you tell which cases work with ATX motherboards and which are designed for Baby-AT or LPX motherboards? Tower cases designed for ATX and Mini-ITX motherboards have a cut-out on the back side for the I/O shield and have an on-off switch that connects to the motherboard, whereas cases designed for the Baby-AT motherboard are designed to use the hardwired power switch, which is part of the LPX power supply. LPX motherboards have a single row of ports along one edge of the rear of the case.

Tower-based, low-cost retail systems sold for home and small-office use typically use a micro-tower configuration. Some micro-tower systems support as many as five drives, whereas others support no more than three. Some use ATX power supplies, whereas others use the lower-power SFX power supplies. The major distinguishing factor separating micro-tower from larger tower cases is the motherboard types supported: Micro-tower designs support only Micro-ATX, Flex-ATX, and Mini-ITX motherboards.

Desktop Cases

A traditional desktop case stands upright on the long side. Although desktop cases with internal layouts comparable to tower cases were once quite popular, they are scarce today. Some vendors produce so-called convertible cases, which can be used in both tower and desktop configurations. These systems typically offer removable drive bays, which enable optical drives to run in the flat position whether the case is upright (tower) or lying down (desktop). Some vendors also provide removable feet, which can be attached to stabilize the system when it is used as a tower.

Slimline and Small Form-Factor Cases

Corporate desktop computers that formerly used the LPX form factor now often use a Slimline or small form-factor design that supports the NLX, Micro-ATX, or Flex-ATX motherboard designs. These systems can be used in an upright or desktop position, but unlike with tower or convertible tower/desktop cases, the optical drive in a Slimline or small form-factor case must be one that can be run in a vertical position. These case designs might not use industry-standard power supplies, making them more expensive and difficult to maintain.

Factors for Selecting the Best Case for the Job

Consider the following factors when selecting a case form factor:

• Expandability Mid-tower and full-tower cases support the widest range of motherboards and largest number of internal ATA, Serial ATA, and SCSI drives. However, if USB 2.0 or IEEE-1394 external drives are used, any case form factor offers satisfactory expansion opportunities.

• Ease of servicing and upgrading Mid-tower and full-tower cases are the easiest to work with for internal memory, drive, add-on card and processor upgrades, and for routine maintenance.

• Space required If space is at a premium, a Slimline desktop computer that can be used in an upright position takes the least amount of space, whereas a tower system placed on the floor uses the most amount of space.

Selecting a Motherboard Upgrade

If you need to upgrade the motherboard in a system, consider the following factors:

• Case and power supply form factors The replacement motherboard must fit into the current case to be a workable upgrade. Note that if you move to a Pentium 4 motherboard that you might need to upgrade the power supply.

• Processor and memory compatibility While you might be able to reuse the existing memory or processor with a new motherboard, reusing these components might limit the performance or future upgrade path of your system.

• Support for advanced hardware A motherboard that supports the latest technologies ( Athlon XP or Pentium 4 processors, AGP 8x, USB 2.0, IEEE-1394, Serial ATA, six-channel audio, 10/100 or Gigabit Ethernet, and so on) provides greater upgrade options than a motherboard lacking support for these technologies.

• Adequate number of PCI expansion slots Although motherboards with a large number of onboard peripherals reduce the need for expansion slots, you should select a motherboard that offers at least one open PCI expansion slot if the case form factor permits it. An open slot allows for future expansion.

• Vendor support A motherboard is only as good as the vendor that supplies and supports it. Check the quality of the documentation, the warranty, and the availability of support files (BIOS, chipset, audio, and so forth) before selecting a particular motherboard.