CompTIA A+ Cert Guide: Motherboards, Processors, and Adapter Cards

This chapter is from the book 

Foundation Topics: Motherboards and Their Components

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. Figure 3-1 shows an example of a typical motherboard. The various components of the motherboard are called out in the figure. We will be referring to this figure throughout the chapter.

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 location and orientation of these busses will vary depending on the type of form factor used. The form factor is the design of the motherboard, which the case and power supply must comply with. Motherboards can come with integrated I/O ports; these are usually found as a rear port cluster. The motherboard will also have memory slots, which allow a user to add sticks of RAM, thus increasing the computer's total resources. Of course, the motherboard also has expansion slots most commonly used by audio and video cards, although the slots can be used by many other types of cards as well. You will also find mass storage ports for hard drives, CD-ROMs, and DVD-ROMs on the motherboard. After we cover all of these concepts, we'll show how to select, install, and troubleshoot the motherboard. As you can see, the motherboard is the central meeting point of all technologies in the computer. There is a lot to cover concerning motherboards. Let's begin by discussing the system and I/O busses.

The System Bus and I/O 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 Willis 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 the traffic reports on a radio station such as Chicago's WBBM (780 AM), 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 gigabytes 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.

Form Factors

Although all motherboards have some features in common, their layout and size vary a great deal. The most common motherboard designs in current use include ATX, Micro ATX, BTX, and NLX. Some of these designs feature riser cards and daughterboards. The following sections cover the details of these designs.

ATX and Micro ATX

The ATX family of motherboards has dominated desktop computer designs since the late 1990s. ATX stands for "Advanced Technology Extended," and it replaced the AT and Baby-AT form factors developed in the mid 1980s for the IBM PC AT and its rivals. ATX motherboards have the following characteristics:

• A rear port cluster for I/O ports
• Expansion slots that run parallel to the short side of the motherboard
• Left side case opening (as viewed from the front of a tower PC)

There are four members of the ATX family, listed in Table 3-2. In practice, though, the Mini-ATX design is not widely used.

Table 3-2. ATX Motherboard Family Comparison

Motherboard Type	Maximum Width	Maximum Depth	Maximum Number of Expansion Slots	Typical Uses
ATX	12 in	9.6 in	Seven	Full tower
Mini-ATX	11.2 in	8.2 in	Seven	Full tower
microATX	9.6 in	9.6 in	Four	Mini tower
FlexATX	9.0 in	7.5 in	Four	Mini tower, small form factor

BTX

One problem with the ATX design has been the issue of system cooling. Because ATX was designed more than a decade ago, well before the development of today's faster components, it's been difficult to properly cool the hottest-running components in a typical system: the processor, memory modules, and the processor's voltage regulator circuits.

To enable better cooling for these devices, and to promote better system stability, the BTX family of motherboard designs was introduced in 2004. Compared to ATX motherboards, BTX motherboards have the following:

• Heat-producing components such as the process, memory, chipset, and voltage regulator are relocated to provide straight-through airflow from front to back for better cooling.
• The processor socket is mounted at a 45-degree angle to the front of the motherboard to improve cooling.
• A thermal module with a horizontal fan fits over the processor for cooling.
• The port cluster is moved to the rear left corner of the motherboard.
• BTX cases include multiple rear and side air vents for better cooling.
• Because of the standardization of processor and memory locations, it's easy to use the same basic design for various sizes of BTX motherboards; the designer can just add slots.
• BTX tower cases use a right-opening design as viewed from the front.

Although BTX designs are easier to cool than ATX designs, the development of cooler-running processors has enabled system designers to continue to favor ATX. There are relatively few BTX-based motherboards and systems currently on the market.

Figure 3-2 compares typical ATX and BTX motherboard layouts to each other.

NLX

NLX motherboards are designed for quick replacement in corporate environments. They use a riser card that provides power and expansion slots that connect to the right edge of the motherboard (as viewed from the front). NLX motherboards have a two-row cluster of ports along the rear edge of the motherboard.

Most systems that use NLX motherboards are considered obsolete. Figure 3-3 illustrates a typical NLX motherboard and riser card.

Riser Cards and Daughterboards

Riser cards and daughterboards provide two different methods for providing access to motherboard–based resources. In current slimline or rackmounted systems based on ATX or BTX technologies, riser cards are used to make expansion slots usable that would otherwise not be available because of clearances inside the case. Riser card designs can include one or more expansion slots, and are available in PCI, PCI-X (used primarily in workstation and server designs), and PCI-Express designs. Figure 3-4 shows two typical implementations of riser card designs.

The term daughterboard is sometimes used to refer to riser cards, but daughterboard can also refer to a circuit board that plugs into another board to provide extra functionality. For example, some small form factor motherboards support daughterboards that add additional serial or Ethernet ports, and some standard-size motherboards use daughterboards for their voltage regulators.

Integrated I/O Ports

Motherboards in both the ATX and BTX families feature a variety of integrated I/O ports. These are found in as many as three locations: all motherboards feature a rear port cluster (see Figure 3-5 for a typical example), and many motherboards also have additional ports on the top of the motherboard that are routed to header cables accessible from the front and rear of the system.

Most recent motherboards include the following ports in their port cluster:

• Serial (COM)
• Parallel (LPT)
• PS/2 mouse
• PS/2 keyboard
• USB 2.0 (Hi-Speed USB)
• 10/100 or 10/100/1000 Ethernet (RJ-45)
• Audio

So-called "legacy-free" motherboards might omit some or all of the legacy ports (serial, parallel, PS/2 mouse and keyboard), a trend that will continue as devices using these ports have been replaced by devices that plug into USB ports.

Some high-end systems might also include one or more FireWire (IEEE-1394a) ports, and systems with integrated video include a VGA or DVI-I video port and an S-Video or HDMI port for TV and home theater use.

Figure 3-5 illustrates a port cluster from a typical ATX system, but note that BTX systems use similar designs.

Some integrated ports use header cables to provide output. Figure 3-6 shows an example of 5.1 surround audio ports on a header cable. The header cable plugs into the motherboard and occupies an empty expansion slot.

Memory Slots

Modern motherboards include two or more memory slots, as seen in Figures 3-1 and 3-2. At least one memory slot must contain a memory module, or the system cannot start or function.

Memory slots vary in design according to the type of memory the system supports. Older systems that use SDRAM use three-section memory slots designed for 168-pin memory modules. Systems that use DDR SDRAM use two-section memory slots designed for 240-pin modules. DDR3 SDRAM also uses two-section 240-pin memory slots, but the arrangement of the pins and the keying of the slot are different than in DDR2. DDR2 and DDR3 modules cannot be interchanged.

Each memory slot includes locking levers that secure memory in place. When memory is properly installed, the levers automatically swivel into place (see Figure 3-7).

To learn more about memory types and slots, see Chapter 6, "RAM."

Expansion Slots

Motherboards use expansion slots to provide support for additional I/O devices and high-speed video/graphics cards. The most common expansion slots on recent systems include peripheral component interconnect (PCI), advanced graphics port (AGP), and PCI-Express (also known as PCIe). Some systems also feature audio modem riser (AMR) or communications network riser (CNR) slots for specific purposes.

PCI Slots

The PCI slot can be used for many types of add-on cards, including network, video, audio, I/O and storage host adapters for SCSI, PATA, and SATA drives. There are several types of PCI slots, but the one found in desktop computers is the 32-bit slot running at 33MHz (refer to Figure 3-8 in the next section).

AGP

The AGP slot was introduced as a dedicated slot for high-speed video (3D graphics display) in 1996. Since 2005, the PCI Express x16 slot (described in the next section) has replaced it in most new systems. There have been several versions of the AGP slot, reflecting changes in the AGP standard, as shown in Figure 3-8. Note that all types of AGP slots can temporarily "borrow" system memory when creating 3D textures.

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.

PCIe (PCI Express) Slots

PCI Express (often abbreviated as PCIe or PCIE) began to replace both PCI and AGP slots in new system designs starting in 2005. PCIe slots are available in four types:

• x1
• x4
• x8
• x16

The most common versions include the x1, x4, and x16 designs, as shown in Figure 3-9.

PCI Express x1 and x4 slots are designed to replace the PCI slot, and x8 and x16 are designed to replace the AGP slot. Table 3-3 compares the performance of PCI, AGP, and PCI Express slots.

Table 3-3. Technical Information About Expansion Slot Types

Slot Type	Performance	Suggested Uses
PCI	133MBps	Video, network, SCSI, sound card
AGP 1x	266MBps	Video
AGP 2x	533MBps	Video
AGP 4x	1,066MBps	Video
AGP 8x	2,133MBps	Video
PCIe x1	500MBps*	Network, I/O
PCIe x2	1,000MBps*	Network
PCIe x8	4,000MBps*	SLI video
PCIe x16	8,000MBps*	Video (including SLI, CrossFire)

AMR and CNR Slots

Some motherboards have one of two specialized expansion slots in addition to the standard PCI, PCI Express, or AGP slots. The audio modem riser (AMR) slot enables motherboard designers to place analog modem and audio connectors and the codec chip used to translate between analog and digital signals on a small riser card. AMR slots are frequently found on older systems with chipsets that integrate software modems and audio functions.

The AMR was replaced by the communications network riser (CNR) slot, a longer design that can support up to six-channel audio, S/PDIF digital audio, and home networking functions. Some vendors have used the CNR slot to implement high-quality integrated audio. Very few AMR riser cards were ever sold, but some motherboard vendors have bundled CNR riser cards with their motherboards to provide six-channel audio output and other features.

Figure 3-10 compares the AMR, PCI, and CNR slots. Figure 3-11 illustrates the AMR and CNR riser cards.

The AMR or CNR slot, when present, is usually located on the edge of the motherboard. The AMR slot was often found on Pentium III or AMD Athlon-based systems, while the CNR slot was used by some Pentium 4-based systems. Current systems integrate network and audio features directly into the motherboard and its port cluster, making both types of slots obsolete.

To learn more about PCI, PCIe, and AGP slots when used for graphics cards, see Chapter 8, "Video Displays and Graphics Cards." To learn more about installing adapter cards, see "Installing Adapter Cards," later in this chapter.

Mass Storage Interfaces

Motherboards also include mass storage interfaces such as PATA/IDE, SATA, and SCSI. The following sections compare and contrast the appearance and functionality of these interfaces. Table 3-4 provides a quick overview of technical information about these interfaces.

Table 3-4. Technical Information About Mass Storage Interfaces

Interface	Performance	Suggested Uses
SATA 1st generation	1.5Gbps	Hard disk, rewritable DVD
SATA 2nd generation	3.0Gbps	Hard disk, rewritable DVD
PATA/IDE	1.0–1.3Gbps	Rewritable DVD, rewritable CD, Zip, JAZ, REV, tape
SCSI	1.6–3.2Gbps*	Hard disk, tape backup

The following sections describe each of these interfaces in greater detail.

PATA/IDE

Until recently, most motherboards included two or more PATA/IDE (also known as ATA/IDE) host adapters for PATA devices such as hard disks, CD or DVD drives, tape backups, and removable-media drives. Each host adapter uses a 40-pin interface similar to the one shown in Figure 3-12, and can control up to two drives.

Most recent systems use a plastic skirt around the PATA connector with a notch on one side. This prevents improper insertion of a keyed PATA (ATA/IDE) cable. However, keep in mind that some older systems have unskirted connectors and some older ATA/IDE cables are not keyed. To avoid incorrect cable connections, be sure to match pin 1 on the PATA host adapter to the red-striped edge of the PATA ribbon cable.

On systems with a third PATA/IDE host adapter, the additional host adapter is typically used for a RAID 0 or RAID 1 drive array. See your system or motherboard documentation for details. Most current systems now have only one PATA/IDE host adapter, as the industry is transitioning away from PATA/IDE to SATA interfaces for both hard disk and DVD drives.

SATA

Most recent systems have anywhere from two to as many as eight Serial ATA (SATA) host adapters. Each host adapter controls a single SATA drive, such as a hard disk or rewritable DVD drive.

The original SATA host adapter design did not have a skirt around the connector, making it easy for the cable to become loose. Many late-model systems now use a skirted design for the host adapter (see Figure 3-13).

SCSI

SCSI (Small Computer Systems Interface) is a more flexible drive interface than PATA (ATA/IDE) because it can accommodate many devices that are not hard disk drives. The fastest versions of SCSI are comparable in speed to today's SATA. However, SCSI systems are usually used in servers and power workstations, as opposed to regular PCs. The following have been common uses for SCSI:

• High-performance and high-capacity hard drives
• Image scanners
• Removable-media drives such as Zip, Jaz, and Castlewood Orb
• High-performance laser printers
• High-performance optical drives, including CD-ROM, CD-R, CD-RW, DVD-ROM, and others

So-called Narrow SCSI host adapters (which use an 8-bit data channel) can accommodate up to seven devices of different varieties on a single connector on the host adapter through daisy-chaining. Wide SCSI host adapters use a 16-bit data channel and accommodate up to 15 devices on a single connector on the host adapter through daisy-chaining. Narrow SCSI devices and host adapters use a 50-pin or (rarely) a 25-pin cable and connector, while Wide SCSI devices use a 68-pin cable and connector.

Several years ago, SCSI host adapters were found on some high-end desktop and workstation motherboards. However, most recent systems use SATA in place of SCSI, and SCSI host adapters and devices are now primarily used by servers. Currently, SCSI is used primarily for high-performance hard disks and tape backups.

Systems with onboard SCSI host adapters might have one or more 50-pin or 68-pin female connectors similar to those shown in Figure 3-14.

To learn more about storage devices, see Chapter 12, "Storage Devices."

Choosing the Best Motherboard for the Job

So, how do you go about choosing the best motherboard for the job? Follow this process:

• Step 1.Decide what you want the motherboard (system) to do. Because most of a computer's capabilities and features are based on the motherboard, you need to decide this first.

  Some examples:

  If you need high CPU performance, you must choose a motherboard that supports the fastest dual-core or multi-core processors available. If you want to run a 64-bit (x64) operating system, you need a motherboard that supports 64-bit processors and more than 4GB of RAM. If you want to run fast 3D gaming graphics, you need a motherboard that supports NVIDIA's SLI or ATI's CrossFire multi-GPU technologies. If you want to support multimedia uses such as video editing, you'll prefer a motherboard with onboard IEEE-1394a (FireWire 400). If you are building a system for use as a home theater, a system with HDMI graphics might be your preferred choice.

• Step 2.Decide what form factor you need to use. If you are replacing an existing motherboard, the new motherboard must fit into the case (chassis) being vacated by the old motherboard and (ideally) be powered by the existing power supply. If you are building a new system, though, you can choose the form factor needed.

  Some examples:

  Full-size ATX or BTX motherboards provide the most room for expansion but require mid-size or full-size tower cases. If no more than three expansion slots are needed, micro ATX or micro BTX systems fit into mini-tower cases that require less space and can use smaller, less-expensive power supplies. If only one slot (or no slots) are needed, picoATX or picoBTX systems that fit into small form factor cases require very little space.

Installing Motherboards

What keeps a motherboard from sliding around inside the case? 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. Most ATX-family and BTX-family motherboards are held in place by screws that are fastened to brass spacers that are threaded into holes in the case or a removable motherboard tray. Before you start working with motherboards or other static-sensitive parts, see the section "Electrostatic Discharge (ESD)," in Chapter 17, "Safety and Environmental Issues," for ESD and other precautions you should follow.

Step-by-Step Motherboard Removal (ATX and BTX)

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 BTX-family motherboards from standard cases, follow these steps:

• Step 1.Turn off the power switch and disconnect the AC power cable from the power supply.
• Step 2.Disconnect all external and internal cables attached to add-on cards after labeling them for easy reconnection.
• Step 3.Disconnect all ribbon cables attached to built-in ports on the motherboard (I/O, storage, and so on) after labeling them for easy reconnection.
• Step 4.Disconnect all cables leading to internal speakers, key locks, speed switches, and other front-panel cables. Most recent systems use clearly marked cables as shown in Figure 3-15, but if the cables are not marked, mark them before you disconnect them so you can easily reconnect them later.
  

  Figure 3-15 Front-panel cables attached to a typical motherboard, which control system power to the motherboard, 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 a label maker or blank address labels to custom-make your own labels.

• Step 5.Remove all add-on cards and place them on an antistatic mat or in (not on top of) antistatic bags.
• Step 6.Disconnect header cables from front- or rear-mounted ports and remove them from the system (see Figure 3-16).
  

  Figure 3-16 A typical dual-USB header cable that uses an expansion slot bracket.

• Step 7.Disconnect the power-supply leads from the motherboard. The new motherboard must use the same power-supply connections as the current motherboard. See Chapter 5, "Power Supplies and System Cooling," for details about power supply connections.
• Step 8.Remove the heat sink and the processor before you remove the motherboard and place them on an anti-static 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 heat sink requires a lot of downward pressure to remove and if the motherboard is not well supported around the heat sink/processor area.
• Step 9.Unscrew the motherboard mounting screws (refer to Figure 3-1) 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.

• Step 10.Lift the motherboard and plastic stand-off spacers out of the case and place them on an antistatic mat. Remove the I/O shield (the metal plate on the rear of the system which has cutouts for the built-in ports; refer to Figure 3-17) and store it with the old motherboard.
  

  Figure 3-17 An ATX I/O shield and motherboard during installation.

Step-by-Step Motherboard Removal (NLX)

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

• Step 1.As described earlier, disconnect cables from any installed add-on cards.
• Step 2.Remove any add-on cards, remembering to handle the cards by their edges.
• Step 3.Pull the motherboard release lever to disconnect the motherboard from the NLX riser.
• Step 4.Slide the motherboard out of the case.

Preparing the Motherboard for Installation (ATX/BTX)

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

• Step 1.Review the manual supplied with the new motherboard to determine correct sizes of memory supported, processor types supported, and configuration information.
• Step 2.Install the desired amount of memory. See Chapter 6 for details.
• Step 3.Install the processor (CPU) and heat sink as described later in this chapter.
• Step 4.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 section "Processors and CPUs" 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/BTX)

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

• Step 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.
• Step 2.Move brass spacers as needed to accommodate the mounting holes in the motherboard.
• Step 3.Place the I/O shield and connector at the back 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 cutouts on some I/O shields are not completely removed, remove them before you install the shield.
• Step 4.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 3-17).
• Step 5.Reattach the wires to the speaker, reset switch, IDE host adapter, and power lights.
• Step 6.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.
• Step 7.Reattach cables from the SATA drives to the SATA ports on the motherboard. Use SATA port 1 for the first SATA drive, and so on.
• Step 8.Reattach the power supply connectors to the motherboard.
• Step 9.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.
• Step 10.Mount header cables that use expansion card slot brackets into empty slots and connect the header cables to the appropriate ports on the motherboard.
• Step 11.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:

• Step 1.Line up the replacement motherboard with the motherboard rails located at the bottom of the case.
• Step 2.Slowly push the motherboard into place. After the motherboard is connected to the riser card, it stops moving.
• Step 3.Lift and push the motherboard release lever to lock the motherboard into place.
• Step 4.Replace the side panel. If the side panel cannot be replaced properly, the motherboard is not installed properly.

Troubleshooting Motherboards

When you're troubleshooting a computer, there is no shortage of places to look for problems. However, because the motherboard is the "home" for the most essential system resources, it's often the source of many problems. If you see the following problems, consider the motherboard as a likely place to look for the cause:

• System will not start—When you push the power button on an ATX or BTX system, the computer should start immediately. If it doesn't, the problem could be motherboard–related.
• Devices connected to the port cluster don't work—If ports in the port cluster are damaged or disabled in the system BIOS configuration (CMOS setup), any devices connected to the port cluster will not work.
• Devices connected to header cables don't work—If ports connected to the header are not plugged into the motherboard, are damaged, or are disabled in the system BIOS configuration (CMOS setup), any devices connected to these ports will not work.
• Mass storage drives are not recognized or do not work—If mass storage ports on the motherboard are not properly connected to devices, are disabled, or are not configured properly, drives connected to these ports will not work.
• Memory failures—Memory failures could be caused by the modules themselves, or they could be caused by the motherboard.
• Problems installing aftermarket processor heat sinks or replacement cards—You cannot assume that every device fits every system.

The following sections help you deal with these common problems.

System Will Not Start

If the computer will not start, check the following:

• Incorrect front panel wiring connections to the motherboard
• Loose or missing power leads from power supply
• Loose or missing memory modules
• Loose BIOS chips
• Incorrect connection of EIDE/PATA cables to onboard host adapter
• Dead short in system
• Incorrect positioning of a standoff
• Loose screws or slot covers

The following sections describe each of these possible problems.

Incorrect Front Panel Wiring Connections to the Motherboard

The power switch is wired to the motherboard, which in turn signals the power supply to start. If the power lead is plugged into the wrong pins on the motherboard, or has been disconnected from the motherboard, the system will not start and you will not see an error message.

Check the markings on the front panel connectors, the motherboard, or the motherboard/system manual to determine the correct pinouts and installation. Figure 3-18 shows typical motherboard markings for front panel connectors (refer to Figure 3-15 for typical markings on front-panel wires).

Loose or Missing Power Leads from Power Supply

Modern power supplies often have both a 20- or 24-pin connection and a four- or eight-pin connection to the motherboard. If either or both connections are loose or not present, the system cannot start and you will not see an error message.

For details, see Chapter 5.

Loose or Missing Memory Modules

If the motherboard is unable to recognize any system memory, it will not start properly. Unlike the other problems, you will see a memory error message.

Make sure memory modules are properly locked into place, and that there is no corrosion on the memory contacts on the motherboard or on the memory modules themselves. To remove corrosion from memory module contacts, remove the memory modules from the motherboard and gently wipe the contacts off to remove any built-up film or corrosion. An Artgum eraser (but not the conventional rubber or highly abrasive ink eraser) can be used for stubborn cases. Be sure to rub in a direction away from the memory chips to avoid damage. Reinsert the modules and lock them into place.

Loose BIOS Chips

Socketed motherboard chips that don't have retaining mechanisms, such as BIOS chips, can cause system failures if the chips work loose from their sockets. The motherboard BIOS chip (see Figure 3-19) is responsible for displaying boot errors, and if it is not properly mounted in its socket, the system cannot start and no error messages will be produced (note that many recent systems have surface-mounted BIOS chips).

The cycle of heating (during operation) and cooling (after the power is shut down) can lead to chip creep, in which socketed chips gradually loosen in the sockets. To cure chip creep, push the chips back into their sockets. Use even force to press a square BIOS chip into place. On older systems that use rectangular BIOS chips, alternately push on each end of the chip until the chip is securely mounted.

Incorrect Connection of PATA/IDE Cables to Onboard Host Adapter

Many systems are designed to wait for a response from a device connected to a PATA/IDE host adapter on the motherboard before continuing to boot. If the PATA/IDE cable is plugged in incorrectly, the system will never get the needed response, and some systems will not display an error message.

Make sure pin 1 on the cable is connected to pin 1 on the EIDE/PATA device and the corresponding host adapter on the system. Check the motherboard manual for the position of pin 1 on the motherboard's host adapter if the host adapter is not marked properly.

Dead Short (Short Circuit) in System

A dead short (short circuit) in your system will prevent a computer from showing any signs of life when you turn it on. Some of the main causes for dead shorts that involve motherboards include

• Incorrect positioning of a standoff
• Loose screws or slot covers

The following sections describe both possible causes.

Incorrect positioning of a standoff

Brass standoffs should be lined up with the mounting holes in the motherboard (refer to Figure 3-1 for typical locations). Some motherboards have two types of holes: plain holes that are not intended for use with brass standoffs (they might be used for heat sink mounting or for plastic standoffs) and reinforced holes used for brass standoffs. Figure 3.20 compares these hole types.

If a brass standoff is under a part of the motherboard not meant for mounting, such as under a plain hole or under the solder connections, the standoff could cause a dead short that prevents the system from starting.

Loose screws or slot covers

Leaving a loose screw inside the system and failing to fasten a slot cover or card in place are two common causes for dead shorts, because if these metal parts touch live components on the motherboard, your system will short out and stop working.

The solution is to open the case and remove or secure any loose metal parts inside the system. Dead shorts also can be caused by power supply–related problems.

For more about the power supply and dead shorts, see Chapter 5.

Devices Connected to the Port Cluster Don't Work

The port cluster (refer to Figure 3-5) provides a "one–stop shop" for most I/O devices, but if devices plugged into these ports fail, check the disabled ports and possible damage to a port in the port cluster, as described in the following sections.

Disabled Port

If a port hasn't been used before, and a device connected to it doesn't work, be sure to check the system's BIOS configuration to determine if the port is disabled. This is a particularly good idea if the port is a legacy port (serial/COM, parallel/LPT) or is the second network port. Ports can also be disabled using Windows Device Manager.

To learn how to manage integrated ports using the system BIOS setup, see Chapter 4 "BIOS." To learn how to manage hardware using Windows Device Manager, see Chapter 15, "Troubleshooting and Maintaining Windows."

Damage to a Port in the Port Cluster

If a port in the port cluster has missing or bent pins, it's obvious that the port is damaged, but don't expect all types of damage to be obvious. The easiest way to see if a port in the port cluster is damaged is to follow these steps:

• Step 1.Verify that the port is enabled in the system BIOS and Windows Device Manager.
• Step 2.Make sure the device cable is connected tightly to the appropriate port. Use the thumbscrews provided with serial/COM, parallel/LPT, and VGA or DVI video cables to assure a proper connection.
• Step 3.If the device fails, try the device on another port or another system. If the device works, the port is defective. If the device doesn't work, the device or the device's cable is defective.

To solve the problem of a defective port, use one of these solutions:

• Replace the motherboard with an identical model—This is the best solution for long-term use. Note that if you replace the motherboard with a different model you might need to reinstall Windows, or, at a minimum, reinstall drivers and reactivate Windows and some applications.
• Install an add-on card to replace the damaged port—This is quicker than replacing the motherboard, but if you are replacing a legacy port such as serial/COM or parallel/LPT, it can be expensive. If the device that plugged into a legacy port can also use a USB port, use a USB port instead.
• Use a USB/legacy port adapter—Port adapters can be used to convert serial/COM or parallel/LPT devices to work on USB ports. However, note that some limitations might be present. Generally, this is the least desirable solution.

Devices Connected to Header Cables Don't Work

Before assuming that a port that uses a header cable is defective or disabled, make sure the header cable is properly connected to the motherboard. If the system has just been assembled, or if the system has recently undergone internal upgrades or servicing, it's possible the header cable is loose or disconnected.

If the header cable is properly connected to the motherboard, follow the steps in the previous section to determine the problem and solution.

Mass Storage Devices Do Not Work Properly

Mass storage devices that connect to SATA, PATA/IDE, or SCSI host adapters on the motherboard will not work if either of the following are true, as described in the next sections:

• Mass storage ports are disabled in system BIOS or Windows
• Data or power cables are not properly connected to the motherboard or drives

Mass Storage Ports Disabled in System BIOS or Windows

Before assuming a mass storage device is defective, be sure to verify whether the port has been disabled in the system BIOS configuration (CMOS setup or in Windows Device Manager). If you cannot connect the device to another port, enable the port and retry the device. To learn how to manage integrated ports using the system BIOS setup, see Chapter 4. To learn how to manage hardware using the Windows Device Manager, see Chapter 15.

Data or Power Cables Are Not Properly Connected to the Motherboard or Drives

If internal upgrades or servicing has taken place recently, it's possible that data or power cables have become loose or disconnected from the mass storage host adapters on the motherboard or the drives themselves. Before reconnecting the cables, shut down the computer and disconnect it from AC power.

For more about mass storage devices and cabling, see Chapter 12.

Memory Failures

Memory failures could be caused by the modules themselves, or they could be caused by the motherboard. For more information on memory problems and motherboards, see the section "Loose or Missing Memory Modules," earlier in this chapter.

Card, Memory, or Heat Sink Blocked by Motherboard Layout

Internal clearances in late-model systems are very tight, and if you attempt to install some types of hardware in some systems, such as an oversized processor heat sink or a very large video card, it might not be possible because of the motherboard's layout.

Before purchasing an aftermarket heat sink, check the clearances around the processor. Be especially aware of the location of capacitors and the voltage regulator; if the heat sink is too large, it could damage these components during installation. To help verify that an aftermarket heat sink will fit properly, remove the original heat sink from the processor and take it with you to compare its size to the aftermarket models you are considering.

Before purchasing an expansion card, check the slot clearance to be sure the card will fit into the desired expansion slot. In some cases, you might need to move a card from a neighboring slot to make room for the cooling fan shroud on some high-performance graphics cards.