It is the main circuit board for the computer system
Every device in the computer system will either be part of the motherboard or connected to it.
The motherboard shown above is an Asus A8V-VM. This board is designed for AMD processors.
The main parts of the motherboard are:
1 Processor socket
This socket is an AMD 939 pin socket. It is designed for the Athlon X2 processor. Different processors require different sockets and a motherboard must be chosen to suit the processor intended for use.
2 Memory sockets
The board has four memory sockets and accepts DDR 266/333/400MHz memory up to a total of 4GB .
3 Power connector
The power supply connects here and supplies appropriate power to the different components on the motherboard.
4 Primary IDE
Hard drives can be either IDE (Integrated Drive Electronics) or SATA (Serial Advanced Technology Attachment). If an IDE hard drive is being used, it should connect to this socket.
5 Secondary IDE
This could be used to connect a second IDE drive. This could be a second hard drive or an Optical drive - DVD or CD drive.
6 CMOS RAM chip
A DRAM chip used to store the date and time and any user settings added to the setup screen. Complementary metal oxide semiconductor is the material the chip is made from.
7 CMOS battery
Because the CMOS chip is a DRAM chip, it is volatile and would loose data when the computer is switched off. The battery preserves the data in the CMOS RAM chip when the computer is powered down.
8 SATA connectors Used to connect SATA hard drives and optical drives .
9 BIOS chip
Basic Input/Output System. A chip holding the start-up routine for the computer system. It runs a program to test the hardware of the system. It the test is successful, a single beep is sounded. If not, a series of beeps are sounded and these beep patterns can be used to identify the failing component.
10 South bridge chip
Forms the chipset with the northbridge. Between them they control the buses on the motherboard. Buses are the data pathways between the motherboard components. The south bridge controls the slower buses like the IDE bus, SATA bus, USB bus etc.
11 North bridge chip
Controls the faster buses on the motherboard. These include the front side bus (between the processor and main memory) and the graphics bus.
12 PCI sockets
Peripheral Component Interconnect sockets used to connect expansion cards like modems, network cards, TV tuner cards etc.
13 FDD connector For connecting a floppy disk drive.
The graphics card connects here. Other motherboards have an AGP (accelerated graphics port) slot.
15 Super I/O chip
Controls the serial, parallel, mouse and keyboard ports at the back of the computer system.
16 Network chip Controls the network port at the back of the computer .
17 Audio ports For connecting speakers, microphones etc.
18 USB ports The current standard for connecting peripherals.
19 Network port Used to connect the computer to a network .
20 Video port
Connect the monitor to this port if a PCI-Express graphics card is not being used.
21 Parallel port Largely obsolete. Used to connect printers and scanners.
22 Serial port Largely obsolete. Used to connect external modem etc.
23 PS2 ports The keyboard connects to the purple port and the mouse connects to the green port. Largely replaced by USB.
24 Audio chip Controls the on board audio system.
The flow of data around the computer is controlled by the Chip set. This consists of two chips:
• North bridge: This chip controls the flow of data between memory and the processor. It also controls the flow of data between the processor and the graphic's card.
• South bridge: This chip controls the flow of data to the slower devices. These include USB, IDE, SATA, LAN and Audio devices. It controls the PCI slots and the on board graphics chip. It delegates control of the keyboard, mouse, parallel and serial ports to the Super I/O chip.
A bus is a set of wires through which data can be sent to the different parts of the computer system. Buses connect the major computer derives to each other. The chipset uses the buses to send data around the motherboard. The main buses are:
• Front side bus: Connects the processor to the northbridge.
• Memory bus: Connects the northbridge to the main memory.
• Graphics bus: Connects the northbridge to the PCI-Express or AGP graphics
• Internal bus: Connects the northbridge to the southbridge
• PCI bus: Connects the PCI slots and the onboard graphics to the
• LPC bus: Connects low bandwidth devices to the southbridge. These
include the BIOS chip and the Super I/O chip which controls
the keyboard, mouse, parallel, serial ports etc.
Motherboards are processor specific. The main types available are:
• Socket 478: Intel Pentium IV processors
• Socket 775: Intel Dual Core and Core Duo processors
• Socket 754: AMD Athlon processors
• Socket 939: AMD Athlon 64 processors
• Socket AM2: AMD Athlon X2 processors
The Power Supply
The power supply can be seen from the back of the system unit. The mains cable is plugged into the power supply. A computer power supply has a number of functions:
• It converts the power from Alternating current (AC) as supplied by the electric supplier to Direct current (DC) as required by the computer system.
• It transforms the 240 Volts supplied by the electric supplier into the voltages required by the computer system. The main voltages are:
• 12 volts for the disk drives as they have motors
• 3.3 and 5 volts for the circuit boards in the computer.
• It uses advances power management (APM) to allow the computer go into a standby mode.
• Some have a switch to toggle between 240 volt supplies and 110 volt supplies. The power supple has a number of connectors to connect to the motherboard, drives etc. The main connectors are:
1 Main connector Connects to the motherboard and supplies the 3.3 and 5 volt supply for the board.
2 Molex connector Connects IDE hard drives and optical drives.
3 Berg connector Connects floppy disk drives
4 SATA connector Connects SATA drives