Chapter 3
• Motherboard is considered the most important
element of a computer’s design
• Provides a physical surface on which to mount
electronic components such as resistors,
capacitors, chips, slots and sockets
• Provides a means for expanding and customizing
they system by inserting expansion boards into
• Also referred to as the system board, main board,
and planar board
Motherboards (cont’d)
• The electrical circuits that run across the surface of
the motherboard are called traces
• A collection of traces and conductors is called a
bus. There are many types of busses
– Data bus (Buss width of 8,16,32, and64 bit buss)
– Control bus – activates devices i.e. hard drive
– Power bus – sends electrical power to low consumption devices
– Internal bus – integrated circuit inside CPU
– Memory bus – connect CPU to RAM
– I/O bus (expansion buss) CPU to expansion slots
Motherboards (cont’d)
• A collection of busses is also called a bus
• The Local bus consists of the power bus, data
bus, control bus, and the memory bus
• Local bus is also called memory bus, system
bus or front side bus (FSB)
• The back side bus describes the CPU internal
Form Factors
• Form factor: (footprint) The physical shape or
outline of the motherboard
– Must be considered when upgrading a PC
– Power supply must match the motherboard
• XT, AT and Baby AT
– XT Original IBM PC (1983) 8-bit
– AT slightly larger than XT 16-bit
– Baby AT same size as XT but 16-bit
Form Factors (cont’d)
• ATX (popular until 1996)
– Most common form factor for full-size computers
– Looks like Baby ATX turned 90 degree
– Polarized power supply connector*
– Requires special shaped power supply
– Three common sizes
• ATX – 12.0” x 9.6”
• Micro ATX – 9.6” x 9.6”
• Flex ATX – 7.5” x 9.6”
Form Factors (cont’d)
• Mini ITX: Smaller version of the micro ATX
– Used for small desktop computers and mobile
– Mini ITX - 6.7” x 6.7”
– Nano ITX - 4.7” x 4.7”
– Pico ITX - 3.94” x 2.83”
– Mobile ITX - 2.36” x 2.36”
Form Factors (cont’d)
• LPX designed for low profile desktop or slim
– Does not have expansion slots
– Single expansion slot mounted in the center of the
– Single slot host a bus riser card
– Popular in low priced computers
– Not standard, proprietary center slot is not always
is same place
LPX Motherboard
Form Factors (cont’d)
• NLX Uses a bus riser card but it is located at the end of the
board (the edge of the board actually plugs into the riser
– Standardized
– Sized 9.0” x 10”-13.6”
– Used in Gateway, HP, IBM,NEC and Micron
• BTX Designed to help cool CPU by placing it right by fan
Reduced Number of Fans and noise
Obsolete case
BTX 10.5 x 12.8
Micro BTX 10.5 x 10.4
Nano BTX 10.5 x 8.8
Pico BTX 10.5 x 8.0
NLX Motherboard
Form Factors (cont’d)
• Backplane: a circuit board with an abundance
of slots along the length of the board.
– Not a true form factor
– Used in heavy industry
– There are two types of Backplanes:
• Passive: all typical motherboard circuits and chips are
located on the expansion boards
• Active: contains the usual circuits and chips normally
found on a motherboard
Bus System Architecture
• Originally computers had one bus. It ran at same
speed as the CPU
• As CPU speeds increased high speed frequency
increase inductive reactance occurred with in
the bus system.
• Inductive reactance magnetic or radio
interference actually chokes electron flow.
• Twisted pairs counteracts IR
• Length of wires actually affect data transfer
Bus System Architecture
• Chipsets manage buses of different frequencies
• Originally two chipsets were used:
– North chipset close to CPU connect high speed
devices to CPU (called north bridge)
– South chipset connect low speed devices (south
• Intel phased out North and south bridge and
replaced it with Quick Path Interconnect (QPI)
• AMD phased out and replaced it with
HyperTransport Technologies
Bus System Architecture (cont’d)
• Without chipsets the CPU would be required
to handle all computer data transfers thus
slowing is down.
• Chipsets enable expansion slots
• Chipsets are an integral part of the
motherboard and are not field replaceable.
• If a chipset the entire motherboard must be
Expansion Card Slots
• Expansion card slots provide a quick and easy
method of connecting devices directly to the
motherboard by accepting adapters,
expansion cards, interface cards, and daughter
• Most common expansion slots are PCI Express
• USB and IEEE-1394 (firewire) not true slots but
act like one
Expansion Card Slots (cont’d)
• Peripheral Components Interconnect (PCI)
– 32 Bit
– 66 MHz
– 132 MBps
– 64 Bit
– 266 MHz
– 17 Gbps
• PCI Express (PCI-E)
64 Bit
533 MHZ
34 Gbps
Expansion Card Slots (cont’d)
• MiniPCI and MiniPCIe: smaller versions of full
size PCI and PCIe designed for laptops,
notebooks and other portable devices
• IEEE-1394 (Firewire): like USB eliminate the
need for expansion slots, parallel ports and
serial ports.
– USB is pushing it out of the market
– Can be added with an expansion card.
Expansion Card Slots (cont’d)
• Universal Service Bus (USB) designed to
replace any expansion slot except high data
rate video expansion slot.
– Allows addition of devices without opening case
– Can support 127 devices
– Plug and play
– Devices take turns communicating through USB
port, sending ‘packets’ of data like a network
– USB 2.0 - 480 Mbps (data one way at a time - half duplex)
– USB 3.0 - 5 Gbps (data flow both ways at one – full duplex)
Expansion Card Slots (cont’d)
USB Cables:
• USB 2.0 4 wires:
– 2 data (twisted pair)
– 2 Power
• USB 3.0 10 wires:
2 USB 2.0 data (twisted pair)
2 USB 3.0 data receive (twisted pair)
2 USB 3.0 data transmit (twisted pair)
1 5 volts (+)
1 power ground (-)
1 electrical ground for signal (-)
1 electrical ground for shielding (-)
Expansion Card Slots (cont’d)
• USB ports often identified with a blue
• Upgrading to USB 3.0
– Install expansion card to PCIe slot
– Install drivers
• Accelerated Graphics Port (AGP) Designed
exclusively for video card
– Located close to RAM and CPU
– DIME direct Memory Execute
– Almost obsolete
Expansion Card Slots (cont’d)
• By combining the functions of several
separate technologies into one unit a more
economical device can be produced:
• AMR - Audio/Modem riser
• ACR - Advanced Communication riser
• CNR - Communication and Network riser
• Combine NIC, modem, audio, USB and DSI
System Resources
• Device Manager: Assigns and allocates system
• Access device manager by typing “device
manager” into search box
• Lists hardware devices installed in system
• Properties tab list information about hardware
configuration and resources
• Can view/update/roll back/uninstall drivers,
System Resources (cont’d)
• Search System Information in search box
– Select system summary
Operating system and version
Computer name
User name
Processor type
BIOS version
• I/O Port and memory address
– Memory address range: assigned section of memory
used as temporary data storage
– I/O Port address is assigned for identification
System Resources (cont’d)
• Interrupt Request (IQR): literally interrupt as
processes taking place in the CPU to give
attention to some device such as the keyboard
• IQR are numbered 0-15
– Lower number = higher priority
– Two IRQ assignments can be shared if devices are
not used at same time (scanner and camera)
– IF two devices with same IQR try to access CPU at
same time system locks up
– Hardware and software IQR exist
System Resources (cont’d)
• Direct Memory Access (DMA) a combination
of hardware and software that allows then
hard drive to directly transfer data to memory
without involving the CPU
– DMA controller is a chip that controls the DMA channels
• Bus Mastering takes control of the busses
involved in DMA and allows devices to
carryout tasks with without involving CPU
System Resources (cont’d)
• Plug and Play: automatic assignments of
system resources
– Simply plug the device in and the computer
configures it
– Before Plug and Play techs needed to
• Set jumpers
• Set dip switches
• Load drivers
Installing Software Drivers
• Install drivers before installing hardware
• Avoids O/S from selecting a generic driver which
may not work
• Drivers are usually supplied on a CD/DVD with the
• Device driver has rollback and update driver options
• Motherboard chipsets also have drivers
– Use custom install –choose exactly what software you
– Default install will load lots of extra/unwanted software
Upgrading BIOS
• Upgrading BIOS common when upgrading
hardware in older systems
• To Upgrade BIOS
– Older systems required new chip
– EPROM: Remove foil label and shine ultraviolet light
into hole under label to erase chip then reprogram
– EEPROM (Flash BIOS) easily erased electronically
then updated using software from the motherboard
manufacturer’s website
Upgrading BIOS (cont’d)
General instructions for upgrading flash BIOS
1. Download new BIOS from website
2. Copy BIOS onto Flash drive
3. Boot PC with flash drive inserted
4. Run BIOS upgrade program
5. When asked, type exact name of BIOS file
6. IF asked if you want to backup existing BIOS – YES
7. When procedure is complete REBOOT PC
8. Enter setup utility and set it to its default settings
9. Save changes and REBOOT
10. During reboot enter SETUP and correct date/time/settings
11. Save changes and reboot one more time
Upgrading BIOS (cont’d)
• Alternate BIOS upgrade (if equipped)
• USB Flashback button found on back of
• Insert USB flash drive with new BIOS into
white USB 2.0
• Press button
• BI(OS firmware is automatically updated!
Setup Utility
• Setup utility allows you to
– Identify type of hard drive
– Identify chipset
– Set password for setup utility
– Select power management features
– Configure boot order
– Setup utility is activated by a special set of keystrokes
displayed during startup (or check motherboard
manufacturer’s website)
– Move jumper to “clear CMOS” and back to clear P/W*
Troubleshooting Motherboards
• Motherboard manufacturer include drawings
of motherboards with component locations in
user guides and websites
• Motherboard is one of the most expensive
parts to replace
• Trouble shooting may require third party
diagnostic software or hardware
• First trouble shoot failed hardware to ensure it
is not the problem (i.e. modem not working)
Troubleshooting Motherboards
• Check for loose connections unplug and plug
connections and jumpers
• Remove and reinstall the CPU
• Check for signs of high voltage damage
• If problem disappears when case is removed check
for pinched cables
• Check motherboard manufacturers website for
information and procedures
• After all methods of diagnostic have been exhausted
motherboard must be changes to be sure
End of Chapter 3
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