Motherboards 1
Motherboards
Overview ............................................................................................................................. 1
Form Factors ........................................................................................................................ 2
ATX .................................................................................................................................. 2
MicroATX .................................................................................................................... 4
BTX .................................................................................................................................. 4
ITX ................................................................................................................................... 4
Mini-ITX....................................................................................................................... 4
nanoITX ........................................................................................................................ 5
picoITX ......................................................................................................................... 5
Sockets ................................................................................................................................. 5
Pin Grid Array (PGA) ...................................................................................................... 5
PGA Variants ................................................................................................................ 6
Zero-Insertion Force (ZIF) Sockets .............................................................................. 6
Land Grid Array (LGA) ................................................................................................... 6
Loading Plate ................................................................................................................ 6
Intel Sockets ..................................................................................................................... 6
AMD Sockets ................................................................................................................... 7
Chipsets ............................................................................................................................... 8
Chipset Architecture and Components............................................................................. 8
Intel Chipsets .................................................................................................................. 10
The Relationship Between Sockets and Chipsets ....................................................... 11
Chipset Naming Convention .......................................................................................... 11
Busses ................................................................................................................................ 11
BIOS .................................................................................................................................. 13
Power On System Test (POST) ...................................................................................... 13
CMOS Setup .................................................................................................................. 14
The Boot Process and the Bootstrap Loader .................................................................. 14
BIOS-Loaded Drivers .................................................................................................... 14
Flashing the BIOS .......................................................................................................... 15
CMOS RAM and the Real Time Clock ............................................................................. 15
Password Protection ....................................................................................................... 15
Losing CMOS Settings................................................................................................... 16
Replacing the CMOS Battery......................................................................................... 16
Overview
This document describes motherboard
form factors, sockets, chipsets,
expansion bus and slots, BIOS, and
other components. The table to the
right from canardpc.com/statscpuzcm-en.html outlines motherboard
market shares as of 2/10/2010. It
M.A.M. 02/03/2011
Company
Asus
Gigabyte
Micostar International (MSI)
Dell
Intel
Market Share
(%)
29.2
17
8.9
4.6
3.4
Motherboards 2
should be noted that Dell and HP do
not manufacture their own boards.
Lenova
Acer
Elitegroup Computer Systems (ECS)
Biostar
HP
Others
3.1
3.1
2.9
2.3
2.2
23.4
Form Factors
Form factors define motherboard dimensions, mounting hole positions, and power supply
connections. The table below provides a historical overview of form factors.
Release Date
1981
1983
1984
1986
1984
1987
1996
1998
Name
Dimensions
PC
9" x 13"
XT
9" x 13"
AT
12" x13.8"
XT-286
9" x 13"
Baby AT
9" x 13"
LPX
NLX
WTX
14" x16.75
ATX*
12 x 9.6
1996 - 2004
microATX*
9.9 x 9.6
flexATX
9 x 7.5
BTX
12.8 x 10.5
2003
microBTX
10.4 x 10.5
picoBTX
8.0 x 10.5
Mini-ITX*
6.7" x 6.7'
2001
Nano-ITX
4.7 x 4.7
2007
Pico-ITX
3.9 x 2.8
* The most relevant form factors today
Comments
Legacy
Sponsored by Intel - Still the most
important form factor family
today.
Sponsored by Intel - No longer
supported as of 2006
Sponsored by VIA. Mini-ITX is
also sponsored by Intel
ATX
Date
1996
1997
2000
2002
2004
Version
ATX
ATX v 2.01
ATX v 2.03
ATX v 2.1
ATX v 2.2
ATX (Advanced Technology Extended) is a computer form
factor created by Intel in 1995 as an open specification. It
encompasses computer case, motherboard, and power supply
design. The ATX specification has been revised several times
since its original release, as indicated in the table to the left.
The ATX board itself measures a maximum of 12 by 9.6 inches. It provides sufficient
space for about seven expansion slots, which are spaced at the conventional 0.8 inches
apart. Mounting holes for the ATX family of form factors is shown in the diagram below:
M.A.M. 02/03/2011
Motherboards 3
Form Factor
Mounting holes
Maximum Size
ATX
A, C, F, G, H, J, K, L, M
12" x 9.6"
microATX
B, C, F, H, J, L, M, R, S
9.6" x 9.6"
FlexATX
B, C, F, H, J, S
9.0" x 7.5"
1
miniITX
C, F, H, J
6.6 x 6.7
1. miniITX (discussed in a later section) is the FlexATX form factor scaled to a minimum
size allowing for the C, F, H and J ATX mounting holes.
Following is a list of guidelines, taken from specification documents, that apply to both
ATX and microATX form factors.
Feature
Power Connector
Back panel I/O Aperture
Disk I/O Connectors
Front Panel I/O Connectors
M.A.M. 02/03/2011
Comment
Should be right edge of board near the processor
Must be 6.25" x 1.75"
Should be front edge of board near the drive bays.
Should be front edge of board.
Motherboards 4
Feature
Memory Module
Connectors
Expansion Slot Connectors
Comment
Should be between processor and expansion slots,
or between processor and disk I/O connectors.
Must be below the CPU parallel to the short edge.
MicroATX
The MicroATX board itself measures a maximum of 9.6 by 9.6 inches which allows for
about four expansion slots. These slots can be any combination of PCI, PCI-X, PCI-e,
CNR, and AGP. Most ATX specifications also apply to microATX.
BTX
Intel announced the (Balanced Technology Extended) BTX standard in 2003 with the
goal of optimizing computer cooling efficiency. It is not backwards compatible with the
ATX form factor, but it does use the same power connector.
All BTX boards are 10.5 inches deep and can vary in width per designation as indicated
in the table below.
Designation
BTX
microBTX
nanoBTX
picoBYX
Max Width
12.8"
10.4"
8.8
8"
# Card Slots
7
4
2
1
In 2007, Intel announced that it will no longer build motherboards based on the BTX
form factor, but will support legacy boards.. The last Intel motherboard manufactured to
BTX specifications contained the 965 chipset (released in 2006) which supported the
Intel Pentium 4, Pentium 4 HT, Pentium D, Celeron D, Core2 Extreme, and Core2 Duo
processors. The most recent BTX motherboard that the instructor could find on
pricewatch.com was manufactured by Elitegroup Computer Systems (ECS) and had an
LGA775 socket and Intel X38 chipset (released in 2007) that supported Core 2
Quad/Core 2 Duo/Core 2 Extreme processors
ITX
The ITX form factor family consists of three members: miniITX, nanoITX, and
picoITX. They are open source specification created by VIA and adopted by the Small
Form Factor Special Interest Group (SFF-SIG).
Mini-ITX
The Mini-ITX board itself measures a maximum of 6.7 by 6.7 inches which is sufficient
for about one expansion slot. It is the FlexATA form factor scaled around ATX mounting
holes C, F, H, and J. That means that a miniITX motherboard could theoretically be used
in a flexATA, microATA, or ATA case. However, most miniITX are deployed in very
M.A.M. 02/03/2011
Motherboards 5
small cases specially created specifically for them. The table below provides an outline of
current miniITX motherboard manufacturers.
Manufacturer
Intel
Jetway
VIA
Zotac
MSI
Processors Supported
 Embedded Atom D410, 510( passively cooled)
 Atom N 230 (fanless), 330 (dual core)
 LGA775 processors (Core 2 dual and quad core)
VIA C7
Intel Atom N230, N330
VIA C7
Atom n230 (fanless); N330 (dual core)
LGA 775 processors
Atom 230 (fanless)
nanoITX
The nanoITX form factor measures 4.7" x 4.7". It appears that no manufacturer is
currently building a nanoITX motherboards.
picoITX
The picoITX form factor (3.9" x 2.8") is only produced by VIA in one model. It is
primary use is in vehicles.
Sockets
Sockets are the receptacles that connect CPUs to motherboards. There are two basic types
of CPU sockets in use today: Ping Grid Array (PGA) and Land Grid Array(LGA):
Pin Grid Array (PGA)
A PGA CPU (depicted right) is built with an array of pins
protruding from its lower surface, which can be mated with a
motherboard socket that is constructed with a matching array of
holes. Pins are spaced approximately 0.1" apart so roughly 100 pins
can be placed per square inch of CPU surface area.
Shown left is a variant of PGA known as
Staggered Pin Grid Array (SPGA). SPGA
provides for more pin density than PGA by
offsetting rows. Compare SPGA to PGA,
shown to the right.
PGA
M.A.M. 02/03/2011
SPGA
Motherboards 6
PGA Variants
A standard PGA or SPGA CPU has the die facing upward on the bottom of the package
substrate. A new approach has been developed, known as The Flip-chip pin grid array
(FC-PGA or FCPGA), in which CPU die faces downwards on the top of the substrate
with the back of the die exposed. This allows the die to have more direct contact with the
heat sink or other cooling mechanism.
As mentioned above, the pin spacing for a regular PGA sockets is approximately 0.1". A
variant has been developed, known as microPGA (mPGA), in which spacing is cut in half
to approximately 0.05". This socket type is often used with mobile processors to save
space.
Different materials have been used as CPU package substrates which are known as minor
PGA variants, as listed in the table below.
PGA Variants
Plastic PGA (PPGA)
Ceramic PGA (CPGA)
Organic PGA (OPGA)
CPU Package Substrate
Plastic
Ceramic
Organic Plastic
Zero-Insertion Force (ZIF) Sockets
ZIF sockets are used on most PGA motherboards to make CPUs easier to install, and to
help prevent bending pins. Before a CPU is inserted into a ZIF socket, a lever on the side
of the socket is moved, pushing away the spring-loaded contacts. The CPU is then
essentially just dropped into the socket. The lever is then moved back, allowing the
contacts to close and securely grip the CPU pins.
Land Grid Array (LGA)
An LGA CPU (shown left) is built with an array of lands, or pads,
along its lower surface, which can be mated with a motherboard
socket that is constructed with a matching array of short, stocky
pins. Because of the higher pin density that can be achieved with
LGA, it is the predominant socket technology used today.
Loading Plate
Instead of a ZIF retaining device, LGA CPUs are held in place by a hinged loading plate
that swings down to cover the CPU.
Intel Sockets
A table of modern Intel sockets is provided below:
Name
Slot 1
Package/Pins
Intro
/Layout
Supported CPUs
1997
242 pin slot Pentium II/III SECC, Celeron SEPP, Cyrix II, C3
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Motherboards 7
Name
Intro
Socket 370
1999
Socket 423
2000
Socket 478
Socket N
2000
Socket 603
2001
Socket 604
2002
LGA 775
Socket T
LGA 771
Socket J
LGA 1156
Socket H
LGA 1366
Socket B
LGA 1567
LGA 1155
2004
2006
2009
Package/Pins
/Layout
SPGA/370
/37 x 37
SPGA/423
/39 x 39
mPGA/478
/26 x 26
mPGA/603
31 x 25
mPGA/604
31 x 25
LGA/775
30 x 33
LGA/771
30 x 33
LGA/1156
40 x 40
2010
LGA/1366
41 x 43
LGA/1567
2011
LGA/1155
2008
Supported CPUs
Pentium III, Celeron, VIA Cyrix III, C3
Pentium 4 (Willamette only)
Intel Pentium 4, Celeron, Pentium 4, Pentium 4
M
Xeon (server)
Xeon (server)
Intel Pentium 4, Pentium D, Celeron, Celeron D,
Pentium XE, Core 2 Duo, Core 2 Quad, Xeon
Xeon (server)
Core i7 (800 series), Core i5 (700, 600 series),
Core i3 (500 series), Xeon (X3400, L3400
series), Pentium (G6000 series), Celeron (G1000
series)
Intel Core i7 (900 series), Xeon (server)
Xeon (6500/7500 series)
Supports Sandy Bridge processors (replacement
for LGA 1156)
AMD Sockets
A table of modern AMD sockets is provided below:
Name
Slot A
Intro
1999
Socket 462
2000
Socket 940
2003
Socket 939
2004
Socket AM2
2006
Socket F
2006
M.A.M. 02/03/2011
Package/Pins
/Layout
242 pin slot
SPGA/462
/37 x 37
PGA/940
/31 x 31
mPGA/939
31 x 31
mPGA/940
31 x 31
LGA/1207
Supported CPUs
Athlon
Athlon, Duron, Athlon XP , Athlon XP-M,
Athlon MP, Sempron
Athlon 64 FX, Opteron (servers)
Athlon 64, Athlon 64 FX, Athlon 64 X2, Opteron
Athlon 64, Athlon 64 X2
Athlon 64 FX, Opteron (Replaces Socket 940 for
Motherboards 8
Name
Intro
Socket AM2+
2007
Socket AM3
2009
Package/Pins
/Layout
/35x35x2
mPGA/940
31 x 31
mPGA/941
31 x 31
LGA/1207
LGA/1974
Supported CPUs
servers)
Athlon 64, Athlon 64 X2, Phenom
Phenom II, Athlon II, Sempron
Socket C32
2010
Opteron (Replaces Socket F for servers)
Socket C 34
2010
Opteron (Replaces Socket F for servers)
Notes:
1. Socket 939 supports (only) DDR memory whereas AM2 supports (only) DDR2
memory.
2. Socket AM2+ improves HyperTransport speed over socket AM2 (from 1 GHz to
2.6 GHz) and adds split power planes: one for the CPU cores, and the other for the
Integrated Memory controller (IMC).
3. AM2 processors will work on AM2+ motherboards, and vice versa - but only
AM2 performance is realized.
4. The built-in memory controller in AM2/AM2+ processors only supports DDR2
memory.
5. The principal change from AM2+ to AM3 is that AM3 processors support both
DDR2 and DDR3 memory.
Chipsets
Chipsets define motherboard features and capabilities. When you purchase a
motherboard, the chipset should be one of the primary considerations.
Chipset Architecture and Components
Historically, a chipset has been composed of two main chips called a Northbridge and
Southbridge, as shown in the diagram below:
M.A.M. 02/03/2011
Motherboards 9
The Northbridge connects high-speed components, such as the memory controller and
video controller, directly to the CPU via the front-side bus. The Southbridge connects
slower speed components to the CPU indirectly through the expansion bus.
A modern view of chipsets is shown below. With it, the memory and video controllers
are incorporated into the CPU, and the front-side bus and Northbridge are eliminated.
This configuration increases the speed of memory and graphics
M.A.M. 02/03/2011
Motherboards 10
In 2003, AMD was the first CPU manufacturer to implement the above model with its
deployement of the Direct Connect Architecture into its 64 bit chipsets. Intel did the same
in 2009 with the implementation of its QuickPath Interconnect technology into its
Nehalem line of CPUs.
With LGA 1366 Nehalem CPUs, the memory controller is incorporated directly into the
die of each CPU. With the LGA 1156 and LGA 1155 Nehalem CPUs, the entire
Northbridge is incorporated into the CPU die.
Intel Chipsets
Intel started making chipsets in 1989 and has been the industry leader in this field ever
since. The table below provides a list of Intel chipsets in chronological order. It is divided
into three categories according to Southbridge connectivity.
 Category 1 - Those connected by the PCI bus - with a throughput of 133 MBps.
This includes the original 400 series chipsets.
 Category 2 - Those connected with the Advanced Hub Architecture (AHA) with a throughput of 266 MBps. This includes the 800 series chipsets. From this
point forward, Intel refers to the Northbridge as the IO Hub (IOH) and the
Southbridge as the IO Controller Hub (ICH).
 Category 3 - Those connected with the Direct Media Interface version 1.0
(DMI 1.0) - with a throughput of 1 GBps in each direction. This includes the 900
and 5x series chips. DMI v 1.0 is essentially a PCI-e x4 v 1.1 connection.
 Category 4 - Those connected with DMI 2.0, including the latest 6x series, with a
throughput of
Chipset
Series
420xx
430xx
440xx
450xx
8xx
9xx
3x
4x
5x
6x
Chip
Interconnection
PCI bus
AHA
DMI
DMI 2.0
Supported Processors and Other Features
P4 (486)
P5 (Pentium), EDO memory
P6 (Pentium Pro, II, III), AGP, SDRAM
P6 workstation (Pentium Pro, II, III, Xeon), SDRAM
PII, PIII, P4, AGP, DDR memory
Pentium 4/D, Core 2, PCI Express, DDR2 memory
Core 2, PCI Express, DDR2/DDR3 memory
Core 2, PCI Express 2.x, DDR2/DDR3 memory
Nehalem (Core i series), PCI Express 2.x
Sandy Bridge (Core i series Second Generation)
Starting with Nehalem, the Southbridge is connected directly to the CPU. The table
below outlines the top providers of chipsets for Intel processors as of 2/9/2010 (according
to www.canardpc.com/statscpuz-cm-en.html).
M.A.M. 02/03/2011
Motherboards 11
Manufacturer
Intel
VIA
nVidia
SiS
ATi
Market Share (%)
82.5
5.8
4.9
4.3
2.2
The Relationship Between Sockets and Chipsets
The latest Intel sockets and chipsets found on motherboards are listed in the table below.
Chipsets
Socket
Desktop
H55, H57, P55, Q57
X58
P67, H67, H65, H61, Q67
LGA 1156
LGA 1366
LGA 1155
Server
3400, 3420, 3450
5500, 5520
Chipset Naming Convention
Ever since the introduction of the 3x series of desktop chipsets, chipset names have been
comprised of two digits with a one-or-two letter prefix. Generally, the newer and more
capable the chipset, the larger the given number. The chipset prefixes mean the
following:
Prefix
H
P
X
Q
Consumer Segment / Comments
Mainstream. Supports on die graphics
Mainstream performance. Supports discrete graphics,
overclocking.
Leading-edge performance. Supports discrete graphics,
overclocking
Business. Supports on die graphics and management features.
Busses
The following table outlines various bus options that may be available in a modern
computer:
Release
Date
1991
1993
1993
1995
1997
Name
PC Card
(PCMCIA Card)
PCI v1
PCI v21
CardBus
AGP 1.0
M.A.M. 02/03/2011
Speed
Bus
Width (bits)
Throughput
33 MHz
32
133 MB/s
33 MHz
66 MHz
33 MHz
66 MHz
32
64
32
32
133 MB/s
528 MB/s
133 MB/s
533 MB/s
Motherboards 12
1998
2000
2000
2002
2003
2003
2004
2007
2008
2009
Q4
2010
PCI-X v11
AGP 2.0
USB v2
AGP 3.0
PCI-X v21,2
66/133 MHz
66
480 Mb/s
66 MHz
266/533 MHz
PCIe v1 = 2.5
GT/s
ExpressCard v1
USB v2 = 480
Mb/s
PCI Express
2.5 GT/s3 per lane
(PCIe) v1
one direction
5.0 GT/s per lane
PCIe v2
one directional
USB v3
5 Gb/s
PCI v2 = 5.0 GT/s
ExpressCard v2
USB v3 = 5 Gb/s
10.0 GT/s per lane
PCIe v36
one direciton
64
32
1
32
64
528/1056 MB/s
1066 MB/s
60 MB/s
2133 MB/s
2.1/4.2 GB/s
1 serial lane
PCIe v1: 250 MB/s
USB v2: 60 MB/s
4
1 per lane
1 per lane
1
1 serial lane
1 per lane
1x (1 lane) = 250 MB/s5
16x (16 lanes) = 4 GB/s
1x (1 lane) = 500 MB/s
16x (16 lanes) = 8 GB/s
625 MB/s
500 MB/s
625 MB/s
1x (1 lane) = 1 GB/s
16x (16 lane) = 16 GB/s
1. Due to the cost of its 64-bit technology, PCI-X is implemented primarily in server
systems.
2. PCI-X v2 is not widely deployed because it was overshadowed by PCIe v1.
3. Giga transfer per second (GT/s) is a measure of raw (unencoded) serial transfer (one
bit at a time). PCIe uses “8b/10b” encoding which consumes 20% of the bandwidth.
Therefore, one calculates the throughput of a 2.5 GT/s lane as follows:
2.5 GT/s x 1 bit/Transfer x 80% = 2.0 Gb/s
2.0 Gb/s / 8 bits/byte = .25 GB/s = 250 MB/s
4. Actually, a PCIe lane has a bus width of 2-bits when used in full duplex mode. Each
lane consists of two pairs of differentially signaled serial wires and is full-duplex capable.
5. In full-duplex mode, the throughput for PCIe is theoretically doubled those listed in
this table.
6. It will probably be late 2011 or 2012 before products using PCIe v3 enter the market
place.
The chart below compares the throughput (MB/s) of various bus types commonly used in
modern computers.
M.A.M. 02/03/2011
Motherboards 13
USB 3
PCIe 2 (x16)
PCIe 2 (x1)
PCIe 1 (x16)
PCIe 1 (x1)
PCI-X (533)
PCI-X 2 (266)
PCI-X 1 (133)
PCI-X 1 (66)
PCI 2
PCI 1
USB 2
0
1000
2000
3000
4000
5000
6000
7000
MB/s
BIOS
The Basic Input/Output Service (BIOS) is a set of programs stored in a read-only
memory (ROM) chip connected to the Southbridge that perform the following four
functions:
Function
Power-On System Test
CMOS Setup
Bootstrap loader
Driver Loader
Description
Hardware tests performed at startup
A utility for viewing and modifying CMOS setting
Code that finds the boot sector of a loadable operating system
Loads basic drivers need before an operating system is
running.
Power On System Test (POST)
The POST utility tests a computer's main memory, busses, and devices, and invokes the
BIOSs of devices that have their own specific BIOS, such as video adapters, network
adapters, and RAID controllers. Any POST errors are displayed as text messages on the
screen. Errors are often accompanied by beep codes which are helpful for video errors
that cannot be displayed. The interpretation of beep codes varies between BIOS
manufacturers and motherboards. BIOS or motherboard documentation should be
consulted for their meaning.
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8000
Motherboards 14
CMOS Setup
The BIOS CMOS Setup utility is used to update setting in CMOS as well as set the realtime clock (RTC). The CMOS Setup utility is invoked by pressing a key identified in a
message displayed at the beginning of system POST. Example message:
Press <F2> to enter Setup
The key required to enter CMOS Setup is specific to each type of BIOS , as given in the
table below:
Key
F1 or Del
F1 or F2
Del
Esc
F101
BIOS
American Megatrends Inc (AMI) BIOS
Phoenix BIOS
Award BIOS
Microid Research (MR) BIOS
Compaq
The Boot Process and the Bootstrap Loader
Understanding the boot process is important when troubleshooting problems that occur
during startup. The basic boot process is as follows:
 The CPU starts the boot process when it receives voltage after the power button is
depressed. The first thing that it does is read the level of the power good wire to
determine if the voltage provided by the power supply is adequate.
 If the power supply is adequate then the CPU passes control to the BIOS which
starts the POST.
 During POST, the BIOS check critical system hardware.
 At the end of POST, the BIOS passes control to the bootstrap loader which
attempts to locate the boot sector of the first boot device listed in CMOS. If this
fails, it goes down the list of boot devices in order until one is found that has a
valid boot sector.
 After a valid boot sector is found (one that can identify the location of an
operating system), control is passed to the operating system.
 The operating system completes the boot process.
BIOS-Loaded Drivers
The BIOS loads drivers for hardware that needs to be up and running before the operating
system is booted, including the following:
 Hard Drives
 Optical Drive
 Floppy Drive
 USB Controller
 Video Adapter
 Network Adapter
 RAID Controller
 Keyboard
Drivers for hardware such as video adapters, network adapters, and RAID controllers are
often loaded by a BIOS within the device itself.
1
Your HP lab computer uses the F10 key to invoke CMOS Setup.
M.A.M. 02/03/2011
Motherboards 15
Flashing the BIOS
The ROM chip is made up of solid state flash memory that allows the BIOS to be
updated or restored programmatically. Updating the BIOS in this manner is known as
flashing the BIOS. Since a power fluctuation can corrupt the BIOS when flashing, it best
to do so only when absolutely necessary, and only after making a complete BIOS backup.
The manufacturer of your laboratory computers, HP, provides the following methods for
flashing the BIOS. Note that only the ROMPaq diskette method creates a BIOS backup.
Name
Description
DOS based utility that can be used locally or with a Preboot
DOS Flash eXecution Environment (PXE) network adapter to update or
restore the system BIOS.
Windows based utility to locally update or restore the system
HPQFlash
BIOS
Creates a bootable CD that can be used to locally restore or
ROMPaq CD
upgrade the system BIOS
ROMPaq
Creates a bootable 1.44 diskette that can be used to locally
Diskette
restore or upgrade the system BIOS
Backup
Made
No
No
No
Yes
CMOS RAM and the Real Time Clock
The CMOS RAM and Real-Time clock (RTC) are normally combined into one chip that
is incorporated into the Southbridge . The function of CMOS RAM (known simply as
CMOS) is to store system parameters required by the BIOS at boot up. The function of
the RTC is to maintain the system date and time. A small amount of electricity is required
to run the RTC and to maintain data in CMOS. This electricity is supplied externally as
long as the computer is plugged in. When the computer is unplugged, a small battery
located on the motherboard provides the electricity.
Most CMOS setup programs have similar basic options, include the following:






System information
Device options
Boot order
Date and Time settings
Power Management
Password protection
Password Protection
Many CMOS setup programs allow you to setup a boot password and a password to enter
setup itself. These passwords are stored in CMOS and can be reset if you forget them - in
M.A.M. 02/03/2011
Motherboards 16
various ways. The motherboards in your HP laboratory computer, for example, have a
jumper that allows you to clear password settings.
Losing CMOS Settings
As mentioned above, CMOS is dependent upon a small battery mounted on the
motherboard to maintain its settings. If the battery gets to the point where it is not holding
adequate charge, then the first symptom that may occurs is a slippage in system time. If
the battery goes dead, the system time will reset itself to January 1st and CMOS setting
may be lost or set to default values. On systems built after 2002, however, the CMOS
should fall back to factory default settings. Factory defaults may allow the system to
boot, but there is a likelihood that CMOS configuration errors may occur. Some CMOS
setup utilities (such as the one used in your laboratory computers) will allow the user to
backup copies of CMOS configuration settings.
Replacing the CMOS Battery
Refer to the motherboard documentation for proper procedures to replace the CMOS
battery. If documentation is not available, then use the following steps:
 Backup CMOS settings. Data may need to be restored after the new battery is
installed.
 If possible, obtain a replacement battery in advance with the proper voltage.
 Turn off the computer. You have the option of unplugging the computer or leaving
it plugged in. Unplugging it is the safest choice for both you and the equipment,
but leaving it plugged in allows a small amount of voltage to be supplied to the
CMOS during battery replacement so that settings will not be lost.
 Remove the system unit cover and use proper anti-static procedures from this
point forward.
 Locate the CMOS battery on the motherboard. It will be cylindrical in shape and
resemble a watch battery.
 Batteries have a + and - orientation. Make sure you make note of this orientation
when you take the old battery out so that you can use it when putting the new back
in.
 Following are the procedure for removing the battery from your laboratory
computer.
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Motherboards 17
1. Release the battery from its holder by
squeezing the metal clamp that extends
above one edge of the battery. When
the battery pops up, lift it out (see
diagram to the right).
2.Insert the new battery by sliding one
edge under the holder lip with positive
side up. Push the other edge down until
the clamp snaps over the other edge of the
battery.
 Restart the computer, go to CMOS setup, and restore or manually re-enter any lost
settings.
M.A.M. 02/03/2011