A+ Guide to Managing and Maintaining your PC, 6e
Chapter 4 Re-VIEW
Form Factors and Power Supplies
At a Glance
Instructor’s Manual Table of Contents

Overview

Objectives

Teaching Tips

Quick Quizzes

Class Discussion Topics

Additional Projects

Additional Resources

Key Terms
4-1
A+ Guide to Managing and Maintaining your PC, 6e
4-2
Lecture Notes
Overview
Chapter 4 covers the topic of supplying power to a PC. In the introductory sections, the
power supply is linked to the motherboard and the computer case. These three hardware
components are specified and matched by form factors. Major form factors for the
motherboard are presented in historical context, with greatest emphasis on the ATX
form factor. Three important computer cases are also presented: desktop, tower, and
notebook. Following the discussion of various motherboard form factors and computer
cases, focus shifts to basic electrical concepts and devices. The salient items in this
section include voltage, current, resistance, power, closed circuits, and various electrical
components, such as transistors. Once the electrical background is provided, attention
turns toward the description and prevention of three electrical threats: electrostatic
discharge, electromagnetic interference, and power surges. The topic following
electrical threats deals with energy conservation, particularly the implementation of
Energy Star standards in computer devices. The final sections of the chapter explain
how to troubleshoot electrical problems.
Chapter Objectives





Learn about different form factors and computer cases
Learn how electricity is measured
Learn how to protect your computer system against damaging changes in electrical
power
Learn about Energy Star specifications
Learn how to troubleshoot electrical problems
Teaching Tips
Computer Case, Motherboard, and Power Supply Form Factors
1. Using Figure 4-1, indicate that the computer case, motherboard, and power supply make
up an interconnecting system.
2. Define the term, form factor. Emphasize that the form factor for the motherboard is
chosen first. The form factors for the computer case and power supply must match.
Review the list of benefits that flow from using one form factor for the three hardware
components.
Types of Form Factors
1. Reiterate that form factors apply to power supplies, cases, and motherboards.
A+ Guide to Managing and Maintaining your PC, 6e
4-3
2. Describe the various form factors covered in eight sub-sections. Place special emphasis
on the evolutionary developments between the AT and ATX form factors. Form factors
discussed, along with a few noteworthy features, appear below:








Teaching
Tip
AT (Advanced Technology) form factor (Figure 4-2 to Figure 4-3)
o Specified motherboard dimensions of 12” x 13.8”
o Utilized by IBM AT PC in the 1980s
Baby AT form factor
o Specified motherboard dimensions of 13” x 8.7”
o Industry standard form factor from 1993 to 1997
ATX form factor (Figure 4-4 to Figure 4-7)
o Specified motherboard dimensions of 12” x 9.6”
o Open specification that is most commonly used today
o Includes all AT voltages plus a +3.3-volt circuit
MicroATX form factor
o Reduces the number of I/O slots on the motherboard
BTX (Balanced Technology Extended) form factor (Figure 4-8)
o Focuses on reducing heat and structurally supporting the motherboard
LPX and Mini-LPX Form Factors
o Designed for low-end PC motherboards
NLX Form Factor (Figure 4-9)
o Developed to improve the LPX form factor
Backplane Systems (Figure 4-10 to Figure 4-11)
o Two types: Active and Passive
o Use boards with expansion slots, but little or no circuitry
Inform students that the acronym ATX stands for "Advanced Technology
Extended."
Types of Cases
1. Describe the role of the computer case (or chassis). There are three basic computer case
types: the desktop, the tower, and the notebook. Present each case type in detail. Figure
4-13 can be used to illustrate the difference between desktop and tower cases. Table 4-1
lists a few case and power supply vendors.
Quick Quiz 1
1. The form ____________________ describes the size, shape, and major features of a
hardware component.
Answer: factor
2. ____________________ improved upon AT by making adding and removing
components easier, providing greater support for I/O devices and processor technology,
and lowering costs.
Answer: ATX (Advanced Technology Extended)
A+ Guide to Managing and Maintaining your PC, 6e
4-4
3. True or False: Backplane systems do not use a true motherboard.
Answer: True
4. The classic case with four drive bays and six expansion slots that sits on your desk
doing double duty as a monitor stand is called a(n) ____________________ case.
Answer: desktop
Measures and Properties of Electricity
1. Emphasize that successful PC technicians understand electricity; know how to use
electricity; know how to measure electricity; and can protect computer equipment from
electricity.
2. Review these four basic electrical units: volt, amp, ohm, and watt. Table 4-2 provides a
useful description of each unit, along with applications to computers. Refer students to
Appendix B for greater detail.
Teaching
Tip
There are a number of ways to relate the various electrical quantities. For
example, voltage is directly related to current by the formula voltage = current x
resistance (V = IR). This relationship is known as Ohm's law.
AC and DC
1. Define the critical concepts of alternating current (AC) and direct current (DC).
2. Indicate that power is transmitted at high voltage and low AC for economical reasons.
Before power passes from the utility lines to a home, the voltage is stepped down by a
transformer (see Figure 4-15). For use in the computer, the 110-volt house current has
to be further stepped down to 12 volts or less and then rectified, a process that converts
AC to DC. Acting as both a transformer and rectifier, the power supply performs both
functions.
3. Emphasize that the computer motherboard and peripherals use a low-voltage direct
current, while the monitor utilizes a 110-volt direct current. To further demonstrate how
direct current works, use the analogy of the flow of water current. Just as water flows
from high pressure to low, current flows from high potential (a hot state) to low
potential (a state of rest, also known as ground or neutral)
Teaching
Tip
An AC voltage can be mathematically expressed as a function of time. The
common sinusoidal version of this function is specified and visually represented
at http://en.wikipedia.org/wiki/Alternating_current.
A+ Guide to Managing and Maintaining your PC, 6e
Teaching
Tip
4-5
The term "power" is often interchanged with the term "energy". Advise students
that these quantities are indeed related by a formula, but are distinct physical
concepts. Power is equivalent to the rate of energy transfer; it is expressed in
joules per second, while energy is expressed in joules.
Hot, Neutral, and Ground
1. Using Figure 4-16, illustrate the complete circuit including a power station, a house, and
a device. AC travels from the power station to the house on a hot line. From the circuit
panel in the house, the current travels to various devices, such as computers and lamps.
The AC exits device circuitry and then returns to the power station on a neutral line.
The flow of electricity throughout the complete, closed circuit is driven by the
difference in potential between source and sink located at the power station.
2. Describe short circuits and the role of fuses in protecting devices from excess current
flow. Discuss how grounds are used to dissipate excess current flow at various points
along the circuit. Review the color coding of ground, neutral, and hot wires. Using
Figure 4-17, identify the ground, neutral, and hot wires in a three-prong plug. Indicate
that a receptacle tester (Figure 4-18) can be used to verify the wiring in a three-prong
outlet.
Some Common Electric Components
1. Describe the three types of materials used to make electrical components: conductors,
insulators, and semiconductors.
2. Describe four major electronic components: transistor, capacitor, diode, and resistor.
The author dedicates a sub-section to each of these units. Place particular emphasis on
the transistor, which links the physical machine to binary logic.
3. The symbols for the electronic components, as well as the ground, are shown in Figure
4-19. Figure 4-20 depicts capacitors residing on a motherboard.
Protecting Your Computer System
1. Indicate that there are three major threats to a computer system: static electricity,
electromagnetic interference, and power surges. The following describe each threat, as
well as ways to protect a computer system from them.
Static Electricity
1. Review the threat posed by static electricity (electrostatic discharge or ESD). ESD can
be prevented by using a ground bracelet or ESD gloves. If these safety tools are not
available, the PC technician should touch the case before touching components. The act
of touching the case will dissipate the charge before the component is touched.
A+ Guide to Managing and Maintaining your PC, 6e
4-6
2. Indicate that ESD is particularly severe in dry and cold climates. Also, advise students
that the power cord should always be unplugged before working inside a case. There is
a residual charge in the power supply when the cord is plugged in, even if the power
switch is in the off position. The residual charge can damage the computer and/or cause
shock.
EMI (Electromagnetic Interference)
1. Define electromagnetic interference (EMI). Discuss radio frequency interference (RFI)
as a type of EMI.
2. Identify problems caused by EMI, such as crosstalk. Explain how a tuned-down radio
can be used to detect EMI.
3. Discuss ways to combat EMI: moving the PC to a new location, shielding cables and
the power supply, and using line conditioners.
Surge Protection and Battery Backup
1. Explain that the uneven flow of current can damage the computer in the long-term.
Some disturbance, such as storms, create power surges that can cause immediate
electrical damage.
2. Emphasize the need to filter AC input. Three types of surge protection devices are used:
surge suppressors, power conditioners, and uninterruptible power supplies (UPSs).
They are installed between the house current and the computer. Only devices that have
the UL (Underwriter's Laboratory) logo should be used.
Teaching
Tip
To underscore the need for filtering AC input, remind students that an electrical
component can be damaged by a discharge of just 10 volts.
Surge Suppressors
1. Explain the importance of using surge suppressors (or protectors) to mitigate the effects
of power spikes. Using Figure 4-21, describe the typical features of a surge suppressor.
Discuss how surge protectors work and how they are rated.
2. Emphasize that indicator lights provide critical feedback about whether the surge
suppressor is working properly. Review the list of criteria that surge suppressors should
meet. Advise students to only purchase those devices that meet these criteria.
Power Conditioners
1. Indicate that a power (or line) conditioner performs two tasks: protects a PC from
spikes in power (voltage surges) and regulates voltage during periods of brownouts.
A+ Guide to Managing and Maintaining your PC, 6e
4-7
During a brownout, voltage is raised to compensate for the power reduction. The
process is reversed when the brownout ends.
2. Indicate that power conditioners are rated in watts, volt-amperes (VA), or kilovoltamperes (kVA). Present the formula used to determine the VA required to support a
computer system.
Uninterruptible Power Supply
1. An uninterruptible power supply (UPS) provides the services of a surge protection,
power conditioning, and power backup. A UPS is represented in Figure 4-22. Describe
the three types of UPS: a standby device, an inline device, and a line-interactive device.
A smart (intelligent) UPS is controlled with software. Review the list of extra features
provided by a smart UPS.
2. Specify the three factors to consider when purchasing a UPS:



The UPS rating should exceed the VA load by at least 25 %
Degree of line conditioning
Warranties, guarantees, and service policies
Quick Quiz 2
1. A(n) ____________________ goes back and forth, or oscillates, rather than traveling in
only one direction.
Answer: alternating current (AC)
2. A(n) ____________________ is a device that changes the ratio of current to voltage.
Answer: transformer
3. A(n) ____________________ is an electronic device that can hold an electrical charge
for a period of time and can smooth the uneven flow of electricity through a circuit.
Answer: capacitor
4. True or False. Line conditioners, like surge suppressors, provide no protection against a
total blackout (complete loss of power).
Answer: True
Energy Star Systems (The Green Star)
1. Inform students that Energy Star (Green) standards specified by the E.P.A.
(Environmental Protection Agency) have the objective of reducing overall electricity
consumption, and protecting and preserving natural resources. List the devices that may
receive an Energy (Green) Star.
2. To comply with Energy Star standards, computers usually incorporate standby
programs. When the computer is not used for some period of time, the standby program
A+ Guide to Managing and Maintaining your PC, 6e
4-8
switches the device to sleep mode. While in sleep mode, the device should not use more
than 30 watts of power.
Since the Energy Star program was created in 1992, it has expanded to include a
variety of appliances, equipment, and other electronic devices. In fact, new
homes and buildings may now also qualify for an Energy Star label.
Teaching
Tip
Power-Management Methods and Features
1. Reiterate the point that the Energy Star standards are designed to conserve energy.
2. Identify and the main methods used by computers to meet Energy Star standards:




Advanced Configuration and Power Interface (ACPI)
Advanced Power Management (APM) specification
AT Attachment (ATA) for various drives
Display Power Management Signaling (DPMS)
3. Advise students that ACPI is the current standard used by most desktops and notebooks.
Describe the four energy saving modes S1 – S4. Explain that ACPI power-management
features are controlled from Windows and BIOS (see Figure 4-24). Review the options
in the Power menu of the BIOS Setup Utility.
Energy Star Monitors
1. Describe the Display Power Management Signaling (DPMS).
2. Figure 4-25 shows the Power Options Properties dialog box in Windows XP. Review
the steps for accessing the energy settings in this dialog box.
Troubleshooting the Electrical System
1. Emphasize that electrical problems can occur before or after boot, and can be consistent
or intermittent.
2. The first step to solving a problem is diagnosing symptoms. List the four symptoms that
indicate a possible problem with the electrical system. Review the simple steps that may
help isolate the cause of the problem.
Problems with External Power
1. Define the term brownout. If a brownout is suspected, devices sharing a circuit with a
computer should be checked. Removing one or more devices may increase the voltage
and improve the flow of current into the computer.
2. Line conditioners may be used to monitor and regulate AC input to the PC.
A+ Guide to Managing and Maintaining your PC, 6e
4-9
Problems with Loose Internal Connections
1. Loose internal connections may cause the computer to appear dead or reboot. To isolate
the cause of this problem, remove the case and check all connections from the power
supply to the motherboard and drives (see Figure 4-26).
Problems that Come and Go
1. Intermittent problems come and go. Review the symptoms that may indicate an
intermittent problem with the electrical system after the boot. Indicate that intermittent
problems are generally more difficult to solve than consistent problems, such as a dead
system.
Problems with an Inadequate Power Supply
1. Indicate that the power supply may not meet the needs of newly installed devices. To
test for inadequate power feeds, all devices should be made to work at the same time.
Observed errors could indicate that the power supply needs to be upgraded.
2. To quantitatively determine total wattage needed by a system, multiply the volts in the
circuit by the amps needed by each device and then add all products together. Power
supplies for PCs range from 200 watts to 600 watts.
Problems with the Power Supply, Boards, or Drives
1. Power related problems are primarily due to faulty or inadequate power supply. Power
problems may also be due to excessive power draw down from defective components.
System hangs, intermittent errors, spontaneous rebooting, or inability to boot may be
symptomatic of a power related problem.
2. Multimeter tests help you determine if output voltages of a power supply are correct,
but are not definitive; the problem may be intermittent. Exchanging the power supply
with a known operational supply can aid diagnosis of a power problem. To test for a
defective card, remove nonessential expansion cards and observe that resulting change
in system performance.
3. If it is determined that the power supply is inadequate or faulty, the power supply
should be upgraded or replaced.
Teaching
Tip
Many notebooks use an external AC adapter to step down house voltage to levels
appropriate for a computer. An adapter that outputs uneven voltages will likely
cause electrical damage. Symptoms of faulty adapters include oscillation from
outlet to battery power and excessive heating at power ports. Test the problem by
exchanging adapters. Faulty AC adapters should be immediately replaced.
A+ Guide to Managing and Maintaining your PC, 6e
4-10
Problems with the Power Supply Fan
1. Indicate that defective fans usually hum or whine before they stop working. To fix this
problem, replace the defective fan or entire power supply.
2. If a fan or power supply is replaced, and the fan still does not work, the problem may be
due to a short in another component, such as a drive, the motherboard, or an expansion
card. To test other components for shorts, follow the procedure described in the text.
Problems with the Motherboard
1. An improper contact between the motherboard and chassis can cause a short. To verify
this problem, check for missing or extra standoffs (metal or plastic spacers between the
motherboard and chassis).
2. A burnt out capacitor on the motherboard is a probable sign of a short. Damaged
circuitry on the back of the motherboard also provides evidence of a short.
3. Frayed wires on connections between drives and the motherboard can cause shorts.
Disconnect these cables and then power up the system to determine whether the frayed
wires are interfering with power distribution.
Problems with Overheating
1. Overheating may cause intermittent problems, and may cause the system to reboot or
not reboot at all. Advise students that the temperature inside a case should not exceed
100F.
2. Review the series of tests and tasks that should be performed to diagnose and solve
problems with overheating. Solutions range from the simple to the complex. On the
lower end of the scale, overheating can be solved by removing dust from the power
supply, vents, and the processor heat sink. More involved measures include the
installation of an exhaust fan at the rear of the case (see Figure 4-27).
3. Using Figure 4-28, illustrate how fans and vents should be arranged for the best
airflow. Note that vents on the front and bottom of the power supply provide for better
airflow inside the case (see Figure 4-29).
Replacing the Power Supply
1. A power supply is considered to be a field replaceable unit (FRU).
2. Ensure that replacement power supplies meet the following criteria:
 Uses the correct form factor
 Adequately rated for power in watts
 Has all power connectors needed by your system
A+ Guide to Managing and Maintaining your PC, 6e
4-11
3. Before executing the complete set of installation tasks, the PC technician should
ensure the replacement solves the problem. To perform this test, the technician should
first connect the PC devices in the new supply and then turn the PC on. If the problem
is solved, the replacement procedure can be continued.
4. Review the 15-step power supply replacement procedure.
Quick Quiz 3
1. Energy ____________________ systems and peripherals have the U.S. Green Star,
indicating that they satisfy certain energy conserving standards of the U.S.
Environmental Protection Agency (EPA).
Answer: Star
2. To control power using BIOS, go to the ____________________ setup and access the
Power menu.
Answer: CMOS (complementary metal oxide semiconductor)
3. True or False. The motherboard, like all other components inside the computer case,
should be grounded to the chassis.
Answer: True
4. True or False. A power supply is not considered a field replaceable unit (FRU) for a PC
support technician.
Answer: False
Class Discussion Topics
1. What are the chief differences between the ATX and AT form factors?
2. Compare and contrast the roles played by fuses and ground wires in dissipating the
excessive flow of electrical current.
3. How is the switching function of a transistor used to implement binary code?
4. In the event of a lightning storm, should you rely on a surge suppressor to protect your
equipment or should you unplug your computer?
5. If the fan in a power supply is not working, should you address the problem by
immediately replacing the fan or the power supply? What technical knowledge supports
your response?
Additional Projects
1. In a passive backplane system, processing circuits are placed on a mothercard instead of
a motherboard. The mothercard is inserted into a slot on a backplane, which does not
contain any circuitry. Identify 3 -5 unique benefits gained from the use of this form
factor.
A+ Guide to Managing and Maintaining your PC, 6e
4-12
2. Using Internet search tools, research integrated circuit technology. Provide a high-level
description of an integrated circuit. Identify at least three problems specifically related
to wiring that the integrated circuit solved. Summarize your findings in 2 - 3
paragraphs.
3. Search the Internet for a description of how a surge suppressor works. Summarize the
description in 2 - 3 paragraphs. Your response should refer to three types of wires: hot,
ground, and neutral.
4. Identify three ways that Advanced Configuration and Power Interface (ACPI) improves
the older Advanced Power Management (APM). How do these new features promote
energy conservation? Provide a response in 1- 2 paragraphs.
Additional Resources
1. Motherboard Form Factors:
http://www.webopedia.com/DidYouKnow/Hardware_Software/2005/motherboard_form_factors.asp
2. How Electricity Works:
http://science.howstuffworks.com/electricity.htm
3. Specifications and Developmental History for Transistors:
http://en.wikipedia.org/wiki/Transistor
4. Surge Protectors:
http://www.webopedia.com/TERM/S/surge_protector.html
5. Energy Star Program:
http://www.energystar.gov/index.cfm?c=home.index
Key Terms
 active backplane: A type of backplane system in which there is some circuitry,
including bus connectors, buffers, and driver circuits, on the backplane.
 alternating current (AC): Current that cycles back and forth rather than traveling in
only one direction. In the United States, the AC voltage from a standard wall outlet is
normally between 110 and 115 V. In Europe, the standard AC voltage from a wall
outlet is 220 V.
 ampere or amp (A): A unit of measurement for electrical current. One volt across a
resistance of one ohm will produce a flow of one amp.
 AT: A form factor, generally no longer produced, in which the motherboard requires a
full-size case. Because of their dimensions and configuration, AT systems are difficult
to install, service, and upgrade. Also called full AT.
 ATX: The most common form factor for PC systems presently in use, originally
introduced by Intel in 1995. ATX motherboards and cases make better use of space and
resources than did the AT form factor.
A+ Guide to Managing and Maintaining your PC, 6e
4-13
 ATX12V power supply: A power supply that provides a 12 V power cord with a 4-pin
connector to be used by the auxiliary 4-pin power connector on motherboards used to
provide extra power for processors.
 Baby AT: An improved and more flexible version of the AT form factor. Baby AT was
the industry standard from approximately 1993 to 1997 and can fit into some ATX
cases.
 backplane system: A form factor in which there is no true motherboard. Instead,
motherboard components are included on an adapter card plugged into a slot on a board
called the backplane.
 brownouts: Temporary reductions in voltage, which can sometimes cause data loss.
Also called sags.
 BTX (Balanced Technology Extended): The latest form factor expected to replace
ATX. It has higher quality fans, is designed for better air flow, and has improved
structural support for the motherboard.
 bus riser: Also called a riser card.
 capacitor: An electronic device that can maintain an electrical charge for a period of
time and is used to smooth out the flow of electrical current. Capacitors are often found
in computer power supplies.
 clamping voltage: The maximum voltage allowed through a surge suppressor, such as
175 or 330 volts.
 compact case: A type of case used in low-end desktop systems. Compact cases, also
called low-profile or slim-line cases, follow either the NLX, LPX, or Mini LPX form
factor. They are likely to have fewer drive bays, but they generally still provide for
some expansion.
 data line protector: A surge protector designed to work with the telephone line to a
modem.
 daughter card: A subordinate extension of a motherboard.
 desktop case: The initial screen that is displayed when an OS has a GUI interface
loaded.
 diode: An electronic device that allows electricity to flow in only one direction. Used in
a rectifier circuit.
 direct current (DC): Current that travels in only one direction (the type of electricity
provided by batteries). Computer power supplies transform AC to low DC.
 Display Power Management Signaling (DPMS): Energy Star standard specifications
that allow for the video card and monitor to go into sleep mode simultaneously. See also
Energy Star.
 electromagnetic interference (EMI): A magnetic field produced as a side effect from
the flow of electricity. EMI can cause corrupted data in data lines that are not properly
shielded.
 Energy Star: “Green” systems that satisfy the EPA requirements to decrease the
overall consumption of electricity. See also Green Standards.
 field replaceable unit (FRU): A component in a computer or device that can be
replaced with a new component without sending the computer or device back to the
manufacturer. Examples: power supply, DIMM, motherboard, floppy disk drive.
 FlexATX: A version of the ATX form factor that allows for maximum flexibility in the
size and shape of cases and motherboards. FlexATX is ideal for custom systems.
 form factor: A set of specifications on the size, shape, and configuration of a computer
hardware component such as a case, power supply, or motherboard.
 full AT: Another term for AT.
A+ Guide to Managing and Maintaining your PC, 6e
4-14
 Green Standards: A computer or device that conforms to these standards can go into
sleep or doze mode when not in use, thus saving energy and helping the environment.
Devices that carry the Green Star or Energy Star comply with these standards.
 intelligent UPS: A UPS connected to a computer by way of a USB or serial cable so
that software on the computer can monitor and control the UPS. Also called smart UPS.
 joule: A measure of work or energy. One joule of energy produces one watt of power
for one second.
 line conditioner: A device that regulates, or conditions, power, providing continuous
voltage during brownouts and spikes.
 line-interactive UPS: A variation of a standby UPS that shortens switching time by
always keeping the inverter that converts AC to DC working, so that there is no chargeup time for the inverter.
 low-profile case: Another term for a compact case.
 LPX: A form factor in which expansion cards are mounted on a riser card that plugs
into a motherboard. The expansion cards in LPX systems are mounted parallel to the
motherboard, rather than perpendicular to it as in AT and ATX systems.
 MicroATX: A version of the ATX form factor. MicroATX addresses some new
technologies that were developed after the original introduction of ATX.
 Mini-ATX: A smaller ATX board that can be used with regular ATX cases and power
supplies.
 Mini-LPX: A smaller version of the LPX motherboard.
 NLX: A low-end form factor that is similar to LPX but provides greater support for
current and emerging processor technologies. NLX was designed for flexibility and
efficiency of space.
 notebook case: A type of case used for portable notebook computers.
 ohm (Ω): The standard unit of measurement for electrical resistance. Resistors are rated
in ohms.
 P1 connector: Power connection on an ATX or BTX motherboard.
 P8 connector: One of two power connectors on an AT motherboard.
 P9 connector: One of two power connectors on an AT motherboard.
 passive backplanes: A type of backplane system in which the backplane contains no
circuitry at all. All circuitry in a passive backplane system is contained on a mothercard
plugged into a backplane.
 power conditioner: A line conditioner that regulates, or conditions, power, providing
continuous voltage during brownouts.
 rectifier: An electrical device that converts AC to DC. A PC power supply contains a
rectifier.
 resistor: An electronic device that resists or opposes the flow of electricity. A resistor
can be used to reduce the amount of electricity being supplied to an electronic
component.
 riser card: A card that plugs into a motherboard and allows for expansion cards to be
mounted parallel to the motherboard. Expansion cards are plugged into slots on the riser
card.
 sag: Another term for a brownout.
 sleep mode: A mode used in many “Green” systems that allows them to be configured
through CMOS to suspend the monitor or even the drive, if the keyboard and/or CPU
have been inactive for a set number of minutes. See also Green Standards.
 slimline case: another term for compact case.
 smart UPS: Another term for intelligent UPS.
A+ Guide to Managing and Maintaining your PC, 6e
4-15
 soft power: Another term for a soft switch.
 soft switch: A feature on an ATX or BTX system that allows an OS to power down the
system and allows for activity such as a keystroke or network activity to power up the
system. Also called soft power.
 spikes: Temporary surges in voltage, which can damage electrical components. Also
called swells.
 surge protector or surge suppressor: A device or power strip designed to protect
electronic equipment from power surges and spikes.
 swell: another term for spike.
 tower case: The largest type of personal computer case. Tower cases stand vertically
and can be as high as two feet tall. They have more drive bays and are a good choice for
computer users who anticipate making significant upgrades.
 transformer: A device that changes the ratio of current to voltage. A computer power
supply is basically
 a transformer and a rectifier.
 transistor: An electronic device that can regulate electricity and act as a logical gate or
switch for an
 electrical signal.
 uninterruptible power supply (UPS): A device designed to provide a backup power
supply during a power failure. Basically, a UPS is a battery backup system with an
ultra-fast sensing device.
 volt (V): A measure of potential difference in an electrical circuit. A computer ATX
power supply usually provides five separate voltages: +12 V, -12 V, +5 V, -5 V, and
+3.3 V.
 watt (W): The unit used to measure power. A typical computer may use a power supply
that provides 200 W.