A perfect and easy guide to motherboard

2. MOTHERBOARD
A typical motherboard consists of a number of components like PCI expansion slots, audio
ports, ps/2 mouse and keyboard ports, parallel and serial I/O ports, USB port, ROM bios
chip, CMOS battery, PATA and SATA connectors, memory slot, CPU ,chipset etc.
SYSTEM CLOCK
The system clock is the actual speed of your FSB with out any
enhancements (such as double pumping, or quad pumping) on it. The
system clock is also sometimes just called the bus speed
CLOCK GENERATOR
CLOCK MULTIPLIERS

3. BUS ARCHITECTURE
INTERNAL BUS :- The Internal Bus connects the different components inside
the case: The CPU, system memory, and all other components on the
motherboard. It's also referred to as the System Bus.
EXTERNAL BUS :- The External Bus connects the different external devices,
peripherals, expansion slots, I/O ports and drive connections to the computer.
In other words, the External Bus allows various devices to be added to the
computer. It is generally slower than the system bus. Another name for the
External Bus, is the Expansion Bus.

4. DATA BUS
Data has to be exchanged between devices. Some of the electronic
pathways or wires of the Internal Bus or the External Bus are
dedicated to moving data. These dedicated pathways are called the
Data Bus.
ADRESS BUS
Data is stored, manipulated and processed in system memory. Your
computer has to move information in and out of memory, and it has to
keep track of which data is stored where. it has to transmit that
information to the CPU and other devices. It has to keep a map of the
different address locations in memory, and it has to be able to
transmit and describe those memory locations to the other
components so that they can access the data stored there. The info
used to describe the memory locations travels along the bus is known
as address bus.

5. CHIPSET
A collection of integrated circuits which are designed to function
together as a unit.
NORTHBRIDGE
The main function of Northbridge as the system memory
controller, connecting the processor to RAM. It also support other
fast components, such as the AGP bus.
SOUTHBRIDGE
Which designed to control all of the I/O functions not handled by the
Northbridge, such as USB, Serial, Parallel, ISA bus, PCI bus, system
BIOS, Disk controller, and onboard audio or network adapters.

7. PC Architecture
 CPU controls all operations, following instructions loaded from software
 Instructions are stored in system memory (RAM), loaded from hard disk
storage
 Cache memory improves throughput of instructions from RAM to CPU
 CPU connects to other components via chipset then over different bus
types
 Bus carries address, data, and power
 Expansion bus allows connection of storage devices, adapters, and
peripherals

8. MEMORY
SYSTEM MEMORY
Program code is loaded into RAM so that it can be accessed and
executed by the processor. RAM also holds data (for example, the
contents of a spreadsheet or document) while it is being modified. RAM
is volatile; it loses its contents when power is removed.
ROM BIOS
Is a chip located on all computer motherboards that contains instructions
and setup for how your system should boot and how it operates.
The BIOS includes instructions on how to load basic computer hardware
and includes a test referred to as a POST that helps verify the computer
meets requirements to boot up properly. If the computer does not pass the
POST, you will receive a combination of beeps indicating what is
malfunctioning within the computer.

9. POST
Test computer hardware, ensuring hardware is properly functioning before
starting process of loading operating system.
The steps of a POST :-
Each time the computer boots up the computer must past the POST. Below is
the common steps a POST performs each time your computer starts.
1.Test the power supply to ensure that it is turned on and that it releases its
reset signal.
2.CPU must exit the reset status mode and thereafter be able to execute
instructions.
3.BIOS checksum must be valid, meaning that it must be readable.
4.CMOS checksum must be valid, meaning that it must be readable.
5.CPU must be able to read all forms of memory such as the memory controller,
memory bus, and memory module.
6.The first 64KB of memory must be operational and have the capability to be
read and written to and from, and capable of containing the POST code.
7.I/O bus / controller must be accessible.
8.I/O bus must be able to write / read from the video subsystem and be able to
read all video RAM.

10.  If the computer does not pass any of the above tests, your
computer will receive an irregular POST. An irregular POST
is a beep code that is different from the standard one or two
beeps. This could be either no beeps at all or a combination
of different beeps indicating what is causing the computer
not to past the POST.
CMOS RAM
Is the area where the computer stores its configuration
information, such as whether or not it has a floppy drive, the date
and time for the system, and the number and size of the hard
drives that are installed.

11. RAID SUPPORT
A group of hard disks that operate together to improve performance or
provide fault tolerance and error recovery through data striping, mirroring,
and other techniques.
ADAPTER CARDS
printed circuit card required to allow a computer to support a new device
or enable a computer to communicate with a peripheral; also called
controller card
Sound card
SCSI card
I/O card
Modem card
NIC card/WI-FI card

12. EXPANSION BUS TECHNOLOGY
ISA BUS, EISA, MCA(micro channel architecture), VESA(video
electronics standards association)
PCI BUS – Involved bus mastering technology
BUS WIDTH AND CLOCK SPEED
ISA – 16 bit (8 MHz)
PCI – 32 bit (33 MHz) (133 MBps)
64 bit (66 MHz) (532 MBps)
PCI-X – 64 bit (133 MHz) (1.6 GBps)

13. Bus/Slot Bits Comments
ISA 8 or 16 bits Operates at 8MHz or
8.33MHz.
EISA 32 bits Supports PnP and bus
mastering. ISA slot
compatible.
VL-Bus 32 bits Supports bus mastering.
Compatible with ISA.
MCA 16 or 32 bits Supports PnP and bus
mastering. Older,
proprietary architecture.
PCI 32 bits Supports PnP, bus
mastering, and burst
mode. Utilizes a host
bridge to communicate
with other expansion
slots.
PCI-2 64 bits Supports PnP and bus
mastering. PCI slot
compatible.
AGP 32 or 64 bits Designed for accelerated
graphics and video
processing.

14. Adapter
Card/Bus
Name
Bus Width Details and Descriptions
PCIe x1
x4
x8
x16
Full duplex lets data be sent and received
simultaneously.
Measured in throughput as a multiple of 250 MBps.
For example, a x4 PCIe slot and card can transfer data at
1000 MBps.
(250 MBps x 4 = 1000 MBps)
PCI 64
32
Current standard, 32 bit and 64 bit, shorter than ISA.
Usually white.
32 bit have two inline slots; 64 bit have three.
AGP 32 Dedicated graphics card slot, 32 bit, shorter than PCI.
Brown.
EISA 32 Old technology, slot 8 and 16 bit versions (32 bit EISA).
ISA 16
8
Black.
Common in older PCs.

15. RISER SLOTS and RISER CARD
AMR (Audio Modem Riser)
CNR (Communication and Networking Riser)
ACR (Advanced Communication Riser)
AGP (Accelerated Graphics Port)
Designed to run at the speed required by 3D graphics cards of the
time. Introduced in 1997 with Pentium II CPU.
AGP 1.0 – 266 MBps
AGP 2.0 – 1.06 GBps
AGP 3.0 – 2132 MBps/2.13 GBps
PCIe
A card that plugs into a motherboard and enables other cards to be plugged
into it horizontally.

16. FORM FACTOR
ATX :- 12 in × 9.6 in (305 mm × 244 mm)
MINI ATX :- 11.2 in × 8.2 in (284mm × 208mm)
NLX :- 10 in × 8.9 (254 mm × 228 mm)
BTX :- 12.8 in × 10.4 in (325 mm × 266 mm)
A motherboard form factor just describes the dimensions or size of the
motherboard and what the layout of the motherboard components are.

17. POWER SUPPLY UNIT (PSU)
PSU is responsible for converting AC to 3.3V, 5V, and 12V DC and to
supply power to motherboard and other add-on devices.
 3.3 V and 5V supplies power to the circuit on the motherboard an adapter
cards for normal computer.
 Laptop and Pentium machines use a voltage of 3.3V and lower for the
motherboard.
12V supplies power to the motor-driven devices such as HDD, FDD and
CD ROM drives.
OUTPUT AVAILABLE FOR DIFFERENT PC TYPES
Standard desktop pc – 220-230 watt.
Slimline desktop pc – 100-110 watt.
Tower system and server pc – 300 watt.
Gaming pc – 500 watt.

18. ATX MOTHERBOARD POWER CONNECTOR
The ATX motherboard uses a molex motherboar power connector that
provides 3.3v, 5v, and 12v supplies.
The original ATX 1.x was for a 20 pin connector.
MOBO supporting P4 an Athlon XP processor have an additional square
2 x 2 +12V connector referred to as ATX12V.
The BTX MOBO can use ATX12V power supply.
PSU designs 3 types of connector for add-on devices molex, mini-molex,
and SATA.
MOLEX CONNECTOR :- is a 4-outlet keyed connector used to connect to
3.5” hard drives 5.25” floppy drives and CD-ROM drives.
MINI MOLEX CONNECTOR:- used to connect to 3.5” floppy disk drives.
Yellow cable-12v
Red cable- 5v
Black cable- ground

19. SATA CONNECTOR
Is a 15 pin connector
Pin 1-3 – 3.3V
Pin 7-9 – 5V
Pin 13-15 – 12V
Others - ground

20. 24-pin ATX12V 2.x power supply connector(20-
pin omits the last 4: 11, 12, 23 and 24)
Color Signal Pin Pin Signal Color
Orange +3.3 V 1 13
+3.3 V Orange
+3.3 V
sense
Brown
Orange +3.3 V 2 14 −12 V Blue
Black Ground 3 15 Ground Black
Red +5 V 4 16 Power on Green
Black Ground 5 17 Ground Black
Red +5 V 6 18 Ground Black
Black Ground 7 19 Ground Black
Grey Power good 8 20 No connection
Purple
+5 V
standby
9 21 +5 V Red
Yellow +12 V 10 22 +5 V Red
Yellow +12 V 11 23 +5 V Red
Orange +3.3 V 12 24 Ground Black
The three shaded pins (8, 13, and 16) are data signals, not power.
Pin 20 used to be used for -5VDC in ATX and ATX12V versions
1.2 and earlier. Version 1.2 allowed the omission of this pin,
and versions 1.3 and beyond prohibited this pin.

21. Four wires have special functions:
PS_ON# or "Power On" is a signal from the motherboard to the power supply.
When the line is connected to GND (by the motherboard), the power supply
turns on. It is internally pulled up to +5 V inside the power supply.
PWR_OK or "Power Good" is an output from the power supply that indicates
that its output has stabilized and is ready for use. It remains low for a brief time
(100–500 ms) after the PS_ON# signal is pulled low.
+5 VSB or "+5 V standby" supplies power even when the rest of the supply lines
are off. This can be used to power the circuitry that controls the Power On
signal.
+3.3 V sense should be connected to the +3.3 V on the motherboard or its
power connector. This connection allows for remote sensing of the voltage drop
in the power supply wiring.