Motherboard

A motherboard, also known as a main board, mainboard, logic board or system board, and sometimes abbreviated as mobo, is the central or primary circuit board making up a complex electronic system, such as a computer.

A typical computer is built with the microprocessor, main memory, and other basic components on the motherboard. Other components of the computer such as external storage, control circuits for video display and sound, and peripheral devices are typically attached to the motherboard via connectors or cables of some sort.

There is more information about IBM-compatible personal computers in PC motherboard. Mainboards Most electrical devices have a board where logical processing begins when the device is powered on. In general, this would be identified as the mainboard or the planar board. Usually, only devices where substantial, varied, and complex calculations occur have their mainboards referred to as motherboards. Computers, game consoles, and PDAs will usually be associated with the term motherboard, while TVs, home theater receivers, and home appliances normally will not.

Contents
1 Components of computer motherboards
1.1 Universal
1.2 Expansion slots
1.3 Peripheral and component interfaces
2 Form factors

Components of computer motherboards

Universal
Most motherboards have either these core components or some alternative for providing their functionality.

CPU socket (designed to hold a CPU)
North Bridge and South Bridge (or a single chip providing functionality of both)
RAM slots

Expansion slots
The number and type of expansion slots are determined by the motherboard manufacturer subject to limitations of the core logic chipset. Common slot types include:

ISA
PCI
AGP
PCI Express
Historic systems also used a variety of other expansion buses:

S-100
NuBus
Sun Microsystems' SBus
IBM's Micro Channel Architecture
VESA Local Bus
EISA

Peripheral and component interfaces
These components are found in most modern computers:

IDE controller
Serial ATA controller/s
USB port/s
FireWire port/s
Ethernet interface/s
Floppy Disk Drive controller
PS/2 ports
Soundcard

SCSI, integrated graphics cards, RAID controllers, thermal sensors, Bluetooth connectivity, and Wireless LAN connectivity are some of the optional features available.

Form factors
Motherboards are available in a variety of Form factors, which usually correspond to a variety of Computer case sizes. The following is a summary of some of the more popular sizes available:

PC/XT - the original open motherboard standard created by IBM for the first home computer, the IBM-PC. It created a large number of 'clone' motherboards due to its open standard and therefore became the de facto standard.
AT form factor (Advanced Technology) - the first form factor to gain wide acceptance, successor to PC/XT. Also known as Full AT, it was popular during the 386 era. Obsolete - superseded by ATX.
Baby AT - IBMs successor to the AT motherboard, it was functionally equivalent to the AT but gained popularity due to its significantly smaller physical size.
ATX - the 'evolution' of the Baby AT form factor, it is now the most popular form factor available today.
Mini-ATX - essentially the same as the ATX layout, but again, with a smaller 'footprint'.
microATX - again, a miniaturization of the ATX layout. Currently, it only supports AGP (ie. no PCI Express support) and therefore is not intended for use with high-end graphics and gamings systems; it is commonly used in the larger of the 'cube'-style cases such as the Antec ARIA.
FlexATX - a subset of microATX allowing more flexible motherboard design, component positioning and shape.
LPX - based on a design by Western Digital, it allows for smaller cases based on the ATX motherboard by arranging the expansion cards in a riser (an expansion card in itself, attaching to the side of the motherboard - image). This design allows the cards to rest parallel to the motherboard as opposed to perpendicular to it. The LPX motherboard is generally only used by large OEM manufacturers.
Mini LPX - a smaller subset of the LPX specification.
NLX - a 'low-profile' motherboard, again incorporating a 'riser', designed in order to 'keep up with market trends'. NLX never gained much popularity.
BTX (Balanced Technlogy Extended) - a newer standard proposed by Intel as an eventual successor to ATX.
microBTX and picoBTX - smaller subsets of the BTX standard.
Mini-ITX - VIA's highly-integrated small form factor motherboard, designed for uses including thin clients and Set-top box.
WTX (Workstation Technlogy Extended) - a large motherboard (more so than ATX) designed for use with high-power workstations (usually featuring multiple Central processing unit or Hard disk.
While most desktop PCs use one of these motherboard form factors, notebook computers generally use highly integrated, customized and miniaturized motherboards designed by the manufacturers. This is one of the reasons that notebook computers are difficult to upgrade and expensive to repair - often the failure of one integrated component requires the replacement of the entire motherboard, which is also more expensive than a regular motherboard due to the large number of integrated components in it.

Motherboard