Lesson 2: Differentiate between motherboard components, their
purposes, and properties
The motherboard is a central computer component, and technicians need to be able to differentiate between
different components on the motherboard. Motherboards come in different sizes and support different components,
such as expansion slots, RAM slots, and CPU sockets. They also have a variety of jumpers and connectors that
technicians need to recognize and understand.
Exam need to know...
■■
■■
■■
■■
■■
■■
■■
■■
■■
■■
Sizes
For example: What type of case can a mini-ATX motherboard fit into? What
are some common ITX-based motherboard types?
Expansion slots
For example: What are expansion slots used for in a computer? Are PCIe and
PCI-X compatible with other?
RAM slots
For example: What is a formal name for a RAM stick? What type of RAM
socket is used in a laptop?
CPU sockets
For example: What is the difference between PGA and LGA? What is used to secure a CPU in its socket?
Chipsets
For example: What is the difference between the north bridge and south bridge? Where is the north
bridge on new systems?
Jumpers
For example: What types of jumpers are commonly found on motherboards? How can you connect pins if you
don’t have a jumper?
Power connections and types
For example: How many pins are in the P1 power connector? How many pins are in a typical CPU power
connector?
Fan connectors
For example: How many pins will a fan connector include?
Front panel connectors
For example: What are some common connectors found at the front panel of a computer?
Bus speeds
For example: How does the speed of a bus impact the speed of PCIe devices?
Sizes
Motherboards come in different sizes but still follow basic standards so that they
can be used in different computer cases. The two primary standard families are the Advanced Technology Extended
(ATX) public standards and the ITX standards used primarily by VIA Technologies. ITX is not an acronym but instead
is used as a name.
True or false? ATX-based motherboards are commonly used in desktop computers. Answer: True. Advanced
Technology Extended (ATX)–based motherboards are used
in most desktop computers. They are based on the original AT motherboards and
have been steadily improved and upgraded over the years.
The micro-ATX (also called mATX or µATX) is a smaller version of the ATX but will still fit in any ATX case and uses the
same power connections. The mini-ITX, Nano- ITX, and Pico-ITX are the most commonly used ITX-based
motherboards. Table 1-1 compares their sizes.
TABLE 1-1 Motherboard sizes
MOTHERBOARD TYPE
SIZE
ATX
12 × 9.6 in (305 × 244 mm)
Micro-ATX
6.75 × 6.75 in to 9.6 × 9.6 in
(171.45 × 171.45 mm to 244 × 244 mm )
Mini-ITX
6.7 × 6.7 in (17 × 17 cm)
Nano-ITX
4.7 × 4.7 in (120 × 120 mm)
Pico-ITX
3.9 × 2.8 in (7.2 × 10 mm)
The ATX motherboard is a standard size, but the micro-ATX motherboard size varies. However, both still follow the ATX standard and can be
powered by similar power supplies. A micro-ATX motherboard can fit in an ATX case. ITX-base mother- boards come in a
variety of different sizes, and many are used in smaller devices.
The Wikipedia article on computer form factors (http://en.wikipedia
.org/wiki/Computer_form_factor ) includes some good drawings and pictures showing the different form factors side
by side. Also, VIA Technologies has an extensive list of resources available on the different ITX-based motherboards
here: http://www.via.com.tw/en/initiatives/spearhead/mini-itx/.
Expansion slots
Motherboards include many built-in capabilities, and these can be expanded by
adding additional cards. The types of cards that motherboards supports are dependent on the expansion slots it
includes.
True or false? PCI-X is an upgrade to PCIe.
Answer: False. Peripheral Component Interconnect-Extended (PCI-X) is an upgrade to PCI, not PCI Express (PCIe).
PCI-X is backward compatible to PCI and is most commonly used in servers. That is, you can insert a PCI-X card
into a PCI or a PCI-X slot. PCIe is a newer standard than PCI and PCI-X, and it is not backward compatible with these
standards. That is, you cannot plug a PCIe card into a PCI or PCI-X slot.
True or false? You can plug a PCIe x2 card into a PCIe x4 slot. Answer: True. You can plug smaller
PCIe cards into larger PCIe slots.
The PCIe multiplier indicates how many two-way lanes are supported by a PCIe
card or slot. Cards with more lanes are larger and require larger slots. Smaller cards can still plug into a larger slot—
they just won’t use all of the lanes available in the card. PCIe sizes include PCIe, PCIe x2, PCIe x4, PCIe x8, PCIe x16,
and PCIe x32.
You should know specifically what types of cards can plug into what type of slots. Some are interchangeable, but others
are not. For example, smaller PCIe cards can plug into larger PCIe slots. however, PCIe cards cannot plug into a PCI or PCI-X slot.
Mini-PCI and mini-PCIe cards are used in laptops. You cannot install these cards into a standard PCI or PCIe slot.
True or false? AGP slots are used for dedicated graphics cards.
Answer: True. Accelerated Graphics Port (AGP) is a dedicated expansion slot used for graphics cards.
AGP cards and slots have been largely replaced by PCIe cards in current systems. When available, they were steadily
improved from AGP to AGP 2X, AGP 4X, and
AGP 8X.
A Communications and Networking Riser (CNR) expansion card is used in some systems. These are smaller and are
designed to accept an audio, modem, or network interface card (NIC) installed by the manufacturer.
If you want to see some images of expansion slots, check out bing.com/ images and type in a search phrase such
as PCIe expansion slots.
RAM slots
Random access memory (RAM) circuit boards (also called memory sticks) plug into
available RAM slots on the motherboard. A motherboard will typically have at least two RAM slots, and some have
as many as six.
True or false? A motherboard used for a desktop system will include DIMM slots used for RAM.
Answer: True. Dual in-line memory modules (DIMMs) are memory sticks that plug into RAM slots.
A DIMM includes integrated circuit (IC) memory chips. In contrast, laptops use small outline DIMMs (SODIMMs), which
also hold memory chips but are smaller than a normal DIMM and cannot fit into a DIMM slot.
RAM sticks use Synchronous Dynamic RAM (SDRAM) and come in three primary double data rate (DDR) versions
(DDR, DDR2, and DDR3), and none of the versions are compatible with each other. An important consideration when
replacing RAM is ensuring that the memory stick matches the RAM slot. Different DIMMs have a different number of
pins, as shown in the following list:
■■
DDR DIMM: 184 pins
■■
DDR2 DIMM: 240 pins
■■
DDR3 DIMM: 240 pins
■■
DDR SODIMM: 200 pins
■■
DDR2 SODIMM: 144 pins or 200 pins
■■
DDR3 SODIMM: 204 pins
Ensure that you know the number of pins used in different DDR types, especially for DDR3 DIMMs (240 pins) and DDR3 SODIMM (204
pins). DDR versions are not compatible with each other, and you cannot use SODIMMs in a desktop computer or traditional DIMMs in a
laptop computer.
RAM types and their features are covered more extensively later in this chapter in Objective 1.3, “Compare and
contrast RAM types and features.”
CPU sockets
Central processing units (CPUs) plug into a CPU socket. The CPU is replaceable on most motherboards, but there
are different socket types. When replacing a CPU,
you need to ensure that you have a CPU that can fit into the existing socket. The two primary CPU manufacturers are
Intel and Advanced Micro Devices (AMD), and their sockets are not compatible with each other.
True or false? Many current Intel CPUs use a land grid array (LGA)–based socket that doesn’t include pin holes.
Answer: True. LGA sockets have small pins created as bumps or pads.
The matching Intel CPUs have identical bumps that line up with the bumps in the socket. This creates a strong
electrical connection when the CPU is installed. Some other sockets use pin grid array (PGA), where pins on the CPU
line up with holes in the socket. A ball grid array (BGA) chip uses balls of solder instead of pins or bumps. The CPU is
mounted in the socket and heated to melt the solder balls and hold the CPU in place.
True or false? CPUs are locked into place with a ZIF socket or a flip top case.
Answer: True. Sockets commonly use either a zero insertion force (ZIF) socket or a flip top case. Both methods lock the
CPU in place.
Ensure that you understand the difference between PGA, LGA, and BGA when preparing for the exam. All CPUs are locked into
place by some method, such as use of a ZIF socket or a flip top case.
CPU socket types are covered more extensively later in this chapter in Objective 1.6,
“Differentiate among various CPU types and features and select the appropriate cooling
method.”
Chipsets
Motherboards include a chipset used as an interface between the CPU and the rest
of the computer. These chipsets are one or more ICs and include additional capabilities such as audio, network, or
USB interfaces. A chipset is designed to work with a specific family of CPUs.
True or false? The functionality of the north bridge is included on the CPU in most systems today.
Answer: True. Older chipsets included a north bridge and a south bridge, but most new CPUs include the north
bridge functionality today.
The north bridge (also called the memory controller hub or MCH) provides the primary interface between the CPU
and high-speed devices, such as RAM and a dedicated graphics card when it is used. The south bridge (also called
the I/O controller hub or ICH) provides an interface to everything else.
When a north bridge is used, the bus between the CPU and the north bridge is called the front side bus. The bus
between the north bridge and the south bridge is the internal bus (internal to the chipset). Figure 1-4 shows how this
is laid out.
FIGURE 1-4 CPU using a chipset with a north bridge and a south bridge.
When the CPU includes the north bridge, it interacts directly with the RAM, the PCIe graphics card, and uses a
direct memory interface (DMI) connection to the chipset. Figure 1-5 shows how this looks.
The primary components associated with the north bridge are the CPU, memory, and video. Even though newer systems
do not use the north bridge, the objectives specifically mention it, so you should have a basic understanding of its
capabilities.
FIGURE 1-5 Chipset with the north bridge functionality included with CPU.
True or false? If a computer indicates that the date and time need to be reset each time the computer is turned on,
replace the CMOS battery.
Answer: True. The CMOS battery powers the real-time clock when the computer is turned off, and this error
indicates that the battery is faulty.
Check the CMOS battery if you find that the clock is running slow, CMOS settings are being reset, or the system is
reporting CMOS errors. The CMOS battery is often circular, like a watch battery, but some motherboards use a barrel
shaped battery similar to an AA battery though much smaller. In some chipsets, the real-time clock is integrated into
the chipset. When the clock is in the chipset, these settings can also be stored there.
Check the CMOS battery if any CMOS settings are not being retained after the system is powered off. The date and time settings are
often the most obvious. You might also notice some hardware settings are not retained or that the system boots slowly as it is
rebuilding the configuration data by first trying to rediscover all the hardware.
Jumpers
Motherboards include one or more jumpers used for different purposes. A jumper
provides an electrical connection between two pins, also known as shorting the connection, because it creates an
electrical short.
True or false? You can normally reset the BIOS password by connecting a jumper on the motherboard.
Answer: True. If the BIOS password has been reset or is not known, you can often reset it by connecting pins on
the motherboard with a jumper.
In addition to pins for a BIOS jumper, motherboards commonly have pins that you can short to clear all the CMOS
settings. This returns them to their factory defaults.
You can also reset the BIOS password by shorting the two pins with any piece of metal, such as a screwdriver. This creates the same
electrical short as the jumper. Before doing this, you should ensure that the computer is turned off and unplugged to prevent any
damage.
Power connections and types
A computer power supply convert’s higher-voltage alternating current (AC) provided
from a commercial power source to lower-voltage direct current (DC) needed by the computer. The power supply
includes multiple cables with specific types of connections that plug into different computer components.
True or false? A 6+2 pin connector from the power supply plugs into an 8-pin port on the motherboard to provide
power to PCIe components.
Answer: True. This might be provided as a single 8-pin connector or a 6+2 connector. Older systems used only 6
pins, so the 6+2 connector can be plugged into an older system.
In addition to the PCIe power connector, motherboards will have the following power connectors:
■■
P1; this provides the primary power to the motherboard. It’s rectangular, with two rows of pins, and comes
in both 20-pin and 24-pin versions. It provides 3.3, 5, and 12 VDC to the motherboard.
Secondary motherboard power; this is a 4-pin connector used to provide
12-V power to the motherboard. Systems with multiple CPUs often use two
4-pin connectors (or an 8-pin connector) to provide power to the CPUs
■■
Ensure that you know what type of power is provided to the mother- board (3.3, 5, 12 VDC) and the power connectors commonly found on a
motherboard.
You can view a listing of the specific voltages provided on the different pins from a standard
ATX-based power supply from the following page: http:// en.wikipedia.org/wiki/ATX12V.
Fan connectors
Computers are kept cool with fans, and most fans plug directly into the motherboard. While it’s rare, some fans plug
directly into a power supply connector either directly or with an adapter.
True or false? A CPU fan will plug into a connector near the CPU.
Answer: True. Most CPUs require a fan to keep them cool, and these plug into a connector very close to the CPU.
Fan connectors are typically simple 2-pin, 3-pin, or 4-pin connectors. A 2-pin connector provides ground and 12 VDC
power. A 3-pin connector adds a sensor to report the RPM of the fan. A 4-pin connector adds a pulse-width
modulation (PWM) signal to vary the speed of the fan.
You can plug a 3-pin fan into a 4-pin connector. It should be plugged in so that the PWM signal is not used. It will still work and report the correct
speed of the fan, but it will no longer function as a variable speed fan.
Front panel connectors
Several connectors go from the motherboard to the front panel. These are used for different purposes and will vary
from computer to computer.
True or false? If the front panel light emitting diode (LED) is not lit, the computer does not have any power
applied.
Answer: False. The LED indicates whether the computer is turned on. However, if the computer is plugged in but not
turned on, the LED is not lit but the motherboard has power applied to it.
The front panel power button is connected to the motherboard, and when pressed, it causes the motherboard to
provide full power to the computer. Some other front panel connectors on the motherboard include the
following:
■■
■■
■■
■■
USB connectors;
the computer.
Most computers have one or more USB connectors at the front in addition to the rear of
Audio connectors; these accept tip ring sleeve (TRS) connections for head- phones and/or microphones.
Drive activity LED;
data.
this flashes when the hard drive is reading or writing
Reset button; Pressing this button causes the system to restart. In contrast, pressing the power button
causes the system to power down but not restarts.
You should be familiar with the common connectors and indicators found on any computer and realise that these are connected to the
motherboard. When replacing a motherboard, these need to be reinstalled correctly to ensure that they work just as they did before
replacing the motherboard.
Bus speeds
The speeds of the different buses within a computer determine how fast the computer operates. These are important
for technicians to understand when shopping for a computer and also when replacing components.
True or false? The speed of a bus provides a direct indication of how much data can be transferred over the bus.
Answer: True. Faster bus speeds transfer more data in the same time frame, often rated in megabytes per second
(MB/s)
Many expansion card slots use a crystal, which provides a constant sine wave at a steady frequency. The rate of the
sine wave is expressed as Hertz (such as MHz) and determines the data rate of the bus. Table 1-2 lists some common
speeds and data rates of many expansion slot standards.
TABLE 1-2 Expansion card bus speeds
BUS
BUS SPEED
DATA RATES
PCI (32-bit)
33 and 66 MHz
133 and 266 MB/s
PCI (64-bit)
33 and 66 MHz
266 and 533 MB/s
PCI-X
66, 133, 266, and 533 MHz
533 and 1,064 MB/s,
2.15 and 4.3 GB/s
AGP (2X, 4X, 8X)
66 MHZ
266, 533, 1,066, and 2,133 MB/s
True or false? PCIe transmits data as a continuous stream of data without a clock. Answer: True. PCIe isn’t tied to a
data clock.
PCIe uses multiple two-way lanes to send data. The number of lanes is identified with an x identifier. For example, PCIe
x2 uses two lanes, PCIe x4 uses four lanes, and so on. PCIe standards include PCIe, PXIe x2, PXIe x4, PXIe x8, PXIe x16,
and PXIe x32.
The speed of the RAM and the CPU is directly related to the crystal used for the CPU
and RAM. These speeds are covered in Objective 1.3 and Objective 1.6 later in this chapter.