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1. A motherboard (sometimes alternatively known as the mainboard, systemboard, planar
board or logic board,[1] or colloquially, a mobo) is the main printed circuit board (PCB) found
in computers and other expandable systems. It holds many of the crucial electronic components
of the system, such as the central processing unit (CPU) and memory, and provides connectors
for other peripherals. Unlike a backplane, a motherboard contains significant sub-systems such
as the processor and other components.
Motherboard specifically refers to a PCB with expansion capability and as the name suggests,
this board is the "mother" of all components attached to it, which often include sound cards,
video cards, network cards, hard drives, or other forms of persistent storage; TV tuner cards,
cards providing extra USB or FireWire slots and a variety of other custom components (the term
mainboard is applied to devices with a single board and no additional expansions or capability,
such as controlling boards in televisions, washing machines and other embedded systems).
Prior to the invention of the microprocessor, a digital computer consisted of multiple printed
circuit boards in a card-cage case with components connected by a backplane, a set of
interconnected sockets. In very old designs the wires were discrete connections between card
connector pins, but printed circuit boards soon became the standard practice. The Central
Processing Unit (CPU), memory, and peripherals were housed on individual printed circuit
boards, which were plugged into the backplate.
During the late 1980s and 1990s, it became economical to move an increasing number of
peripheral functions onto the motherboard. In the late 1980s, personal computer motherboards
began to include single ICs (also called Super I/O chips) capable of supporting a set of low-speed
peripherals: keyboard, mouse, floppy disk drive, serial ports, and parallel ports. By the late-
1990s, many personal computer motherboards supported a full range of audio, video, storage,
and networking functions without the need for any expansion cards at all; higher-end systems for
3D gaming and computer graphics typically retained only the graphics card as a separate
component.
The most popular computers such as the Apple II and IBM PC had published schematic
diagrams and other documentation which permitted rapid reverse-engineering and third-party
replacement motherboards. Usually intended for building new computers compatible with the
exemplars, many motherboards offered additional performance or other features and were used
to upgrade the manufacturer's original equipment.
Design
A motherboard provides the electrical connections by which the other components of the system
communicate (talk with each other). Unlike a backplane, it also contains the central processing
unit and hosts other subsystems and devices.
A typical desktop computer has its microprocessor, main memory, and other essential
components connected to the motherboard. Other components such as external storage,
controllers for video display and sound, and peripheral devices may be attached to the

2. motherboard as plug-in cards or via cables, in modern computers it is increasingly common to
integrate some of these peripherals into the motherboard itself.
An important component of a motherboard is the microprocessor's supporting chipset, which
provides the supporting interfaces between the CPU and the various buses and external
components. This chipset determines, to an extent, the features and capabilities of the
motherboard.
Modern motherboards include:
 Sockets(orslots) inwhichone or more microprocessors maybe installed.Inthe case of CPUs in
BGA packages,suchas the VIA C3, the CPU isdirectlysolderedtothe motherboard.[citation needed]
 Slotsintowhichthe system'smainmemoryistobe installed(typicallyinthe formof DIMM
modulescontaining DRAMchips)
 A chipsetwhichformsaninterface betweenthe CPU's front-side bus,mainmemory,and
peripheral buses
 Non-volatilememory chips(usually FlashROMinmodernmotherboards) containingthe
system's firmware orBIOS
 A clockgeneratorwhichproducesthe system clocksignal tosynchronize the various
components
 Slotsforexpansioncards (the interface tothe systemviathe busessupportedbythe chipset)
 Powerconnectors,whichreceiveelectrical powerfromthe computerpowersupply and
distribute ittothe CPU, chipset,mainmemory,andexpansioncards.Asof 2007, some graphics
cards (e.g. GeForce 8 and RadeonR600) require more powerthanthe motherboardcanprovide,
and thus dedicatedconnectorshave beenintroducedtoattachthemdirectlytothe power
supply.[3]
Mostdiskdrives alsoconnecttothe powersupplyviadedicatedconnectors.[citation needed]
Additionally, nearly all motherboards include logic and connectors to support commonly used
input devices, such as PS/2 connectors for a mouse and keyboard. Early personal computers such
as the Apple II or IBM PC included only this minimal peripheral support on the motherboard.
Occasionally video interface hardware was also integrated into the motherboard; for example, on
the Apple II and rarely on IBM-compatible computers such as the IBM PC Jr. Additional
peripherals such as disk controllers and serial ports were provided as expansion cards.
Given the high thermal design power of high-speed computer CPUs and components, modern
motherboards nearly always include heat sinks and mounting points for fans to dissipate excess
heat.
CPU sockets
A CPU socket (central processing unit) or slot is an electrical component that attaches to a
Printed Circuit Board (PCB) and is designed to house a CPU (also called a microprocessor). It is
a special type of integrated circuit socket designed for very high pin counts. A CPU socket
provides many functions, including a physical structure to support the CPU, support for a heat
sink, facilitating replacement (as well as reducing cost), and most importantly, forming an
electrical interface both with the CPU and the PCB. CPU sockets on the motherboard can most
often be found in most desktop and server computers (laptops typically use surface mount

3. CPUs), particularly those based on the Intel x86 architecture. A CPU socket type and
motherboard chipset must support the CPU series and speed.
Integrated peripherals
Blockdiagramof a modernmotherboard,whichsupportsmanyon-boardperipheral functionsaswell as
several expansionslots
With the steadily declining costs and size of integrated circuits, it is now possible to include
support for many peripherals on the motherboard. By combining many functions on one PCB,
the physical size and total cost of the system may be reduced; highly integrated motherboards are
thus especially popular in small form factor and budget computers.
 Diskcontrollers fora floppydiskdrive,upto2 PATA drives,andupto 6 SATA drives(including
RAID 0/1 support)
 integrated graphicscontrollersupporting 2Dand 3D graphics, withVGA and TV output
 integratedsoundcard supporting8-channel (7.1) audioand S/PDIFoutput
 Fast Ethernetnetworkcontrollerfor10/100 Mbit networking
 USB 2.0 controllersupportingupto12 USB ports
 IrDA controllerforinfrareddatacommunication(e.g.withanIrDA-enabledcellularphone or
printer)
 Temperature,voltage,andfan-speedsensorsthatallow softwaretomonitorthe healthof
computercomponent.