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A motherboard, system board, or colloquially, a mobo is a printed circuit board (PCB) found in computers and other expandable systems.

All motherboards have socket name that corresponds with the CPU that can be used, a few are:

  • AMD AM3+, AMD Ryzen™ and AMD FX

  • Intel i7 series LGA 1156 socket H

  • Intel i9 - LGA 2066

A Motherboard holds a few crucial components, such as,

  • Central Processing Unit or the CPU socket.

  • Memory (RAM) slots.

  • Contains important sub-systems.

  • Many have embedded HD video facilities and 7:1 sound.

  • Holds the BIOS (Basic Input Output System) installed.

  • Provides connectors for peripherals, sockets, connections, and slots for:

  • Mouse

  • Keyboard

  • Speakers

  • Network port

  • USB ports

  • Firewire port

  • Hard drives

  • Monitor

  • Video cards

  • Sound cards

  • Network cards

  • TV Tuner cards


Motherboards provide several external connections, so users are able use the computer. It is PCB with expansion capability - the board is the ‘mother’ of most of the components attached.


Different types of motherboard ports and their functions explained.

RJ-45 (Registered Jack 45) LAN port – The RJ-45 port allows connection to a Local Area Network (LAN) through a network hub using an RJ-45 cable.

Analog Audio Ports – allow connections like speakers, audio devices, and microphones.

USB (Universal Serial Bus) 2.0 or 3.0 Ports - are located on each motherboard and used for connecting mice, keyboards, printers/scanners, external hard drives, and tablets.

PS/2 Keyboard Port (purple) - used for a PS/2 keyboard.

PS/2 mouse port (green) - used for a PS/2 mouse.

1394a Port - used to connect firewire devices. FireWire has largely been displaced by USB. However, some professional audio hardware devices still use FireWire.

Optical S/PDIF - used for sound connections to home audio receivers or powered PC speakers with optical connections.

eSATA Port (External Serial Advanced Technology Attachment) - It is an external interface for SATA technologies and competes with FireWire 400 and USB 2.0 to provide fast data transfer speeds for external storage devices.

HDMI Port (High-Definition Multimedia Interface) - is a digital interface for transmitting audio and video data in a single cable. It is supported by most HDTVs and related components, like DVD and Blu-Ray players, cable boxes, and video game systems.

DVI Port (Digital Visual Interface) - is used to send digital information from a computer to a digital display, such as a flat-panel LCD monitor.


There are several types:














DisplayPort (DP) - is a digital display interface developed by a conglomerate of PC and chip manufacturers. The interface is primarily used to connect a video source to a display device,  a monitor, it can also carry audioUSB, and other forms of data.

Initially, the DisplayPort was designed to replace VGA, FPD-Link, Digital Visual Interface (DVI), and the interface is backward compatible with HDMI and DVI, using adapters.









VGA (Video Graphics Array) Port - VGA is an older video format and it allows an analog signal as opposed to a digital signal (ones and zeroes). Using higher frequencies, it is possible to reach a relatively high range of video resolutions. However, video quality directly responds to cable quality, and particularly with higher resolutions. Because of this, the quality of a VGA image can fluctuate with different makes of cable.


Bus Sub-Systems


The motherboard is a circuit board that connects the CPU to the memory and all the other hardware.

Buses are circuits on the motherboard that connect the CPU to other components. There are many buses on the motherboard, bus systems move instructions and data around the system. Bus speed is measured in megahertz (MHz), The faster the bus, the quicker data is communicated, therefore, the motherboards speed is defined by the bus speed.

Bus systems are limited by their width in bits and are usually 8, 16, or 32-bits wide. This indicates how many bits can be sent by the bus at any one time, so, a 32-bit bus can send 32 bits or a 16-bit can send 16 bits at once.

The bus that connects the CPU to the memory is called the front-side bus (FSB) or system bus. CPU cores share Level 2 and Level 3 cache across the front-side bus and will usually connect to Level 2 cache through the back-side bus (BSB), the back-side bus is faster than the FSB.

There are two types of Bus sub-systems:

  • Internal – Buses that connect to internal components.

  • External – Buses that connect to external components.

The FSB contains two types of bus:

  • Address bus - this sends information about where data needs to go by sending an address to the memory. The address bus only sends data in one direction - from the CPU to RAM.

  • Data bus - this sends data to the memory or receives data from the memory. Data can flow both ways along the data bus.

A Bus Sub-system transfers data between computer components. Separate to point-to-point connections, a bus system can logically connect several peripherals over the same set of connections.

Every Bus defines its set of connectors to physically plug devices, cards, or cables together. Because of this, there are various kinds of slots used to connect internal and external devices.

Laptop motherboard closeup showing CPU a

North Bridge: The northbridge typically handles communications among the CPU, in some cases RAM, and PCI Express (or AGP) video cards, and the southbridge. Northbridge is directly connected to AGP video, thus providing higher transfer rates.

SouthBridge: The southbridge is one of the two chips in the core logic chipset on a personal computer (PC) motherboard, the other being the northbridge. The southbridge typically implements the slower capabilities of the motherboard in a northbridge/southbridge chipset computer architecture. A southbridge chipset handles all the computer's I/O functions, such as USB, audio, serial, the system BIOS, the ISA bus, the interrupt controller, and the IDE channels.

closeup of Pci expess port slot on moder

PCI (Peripheral Component Interconnect)

There are many kinds of internal buses, but there are only a few popular ones. Various motherboards have different kinds and a number of slots, so it is vital to know what kind and number of slots a motherboard has before purchasing a sound or video card and match the type of slot to the motherboard.

PCI (Peripheral Component Interconnect) was common in PCs several years ago, now PCIe (Peripheral Component Interconnect Express) has succeeded this type of bus. Usually, PCIe cards used were:

  • Network card or NIC card

  • Sound card

  • Modems

  • Additional USB or Serial ports

  • TV tuner card

  • Additional SATA disk controllers

  • Video card

PCIe (Peripheral Component Interconnect Express)

PCIe was designed to replace the general-purpose PCI expansion bus and the aging AGP graphics card interface. PCIe is not a bus, but a point-to-point connection of serial links called lanes. Because PCIe cards have faster bandwidths than PCI cards they make an ideal option for high-end video cards.

AGP (Accelerated Graphics Port)

AGP (Accelerated Graphics Port) is a high-speed point-to-point channel for attaching graphics cards to motherboards to help in the acceleration of 3D graphics.

Computer mainboard with PCI express expa

Connectors and Motherboard Pins

Motherboards require connectors and Pins to work. Some power the motherboard, while others provide connections for:

  • SATA and IDE (old type connection) Hard drives

  • SATA and IDE DVD/CD writers/players and

  • IDE floppy drive (no longer used)

  • USB, Firewire, Audio (analog and digital), connections for the front of the case, and DVD players

  • Power for fans (including the CPU cooling fan)

  • ATX 24 pin and ATX 6 12-volt motherboard power

  • Front panel pins – computer cases have fitted leads for front USB, Firewire, audio, microphones and:

  • Power Switch

  • Speaker

  • Reset Switch

  • Power LED

  • Chassis Intrusion Header

  • Hard drive activity LED

  • Message/Power Sleep LED


Front panel pins are a conundrum because case manufacturers have not decided on a standard. Some manufacturers use plain coloured wire, others dual coloured and they hardly ever identify with is positive or ground leads. If lucky they put an information sheet in the box, but the cheaper cases tend not to have these.

Luckily, some motherboard manufacturers are more accommodating.

However, all manufacturers do indicate which lead is which by abbreviating on the connector, such as:

  • PWR – Power Switch

  • SPK - Speaker

  • RES - Reset Switch

  • MSG - Message/Power/Sleep LED

  • CH - Chassis Intrusion Header

  • HD - Hard drive activity LED


The pin assignments for the front panel header may differ by model. Refer to the motherboard user's manual for the actual pin assignments.

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