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a board that is a mother
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[[file:Acer E360 Socket 939 motherboard by Foxconn.svg|thumb|Motherboard for an Acer desktop personal computer, showing the typical components and interfaces that are found on a motherboard. This model was made by Foxconn in 2008, and follows the [[ATX]] layout (known as the "[[Computer form factor|form factor]]") usually employed for desktop computers. It is designed to work with AMD's [[Athlon 64]] [[cpu|processor]]]]
[[file:EBMotherboard.JPG|thumb|A motherboard of a Vaio E series laptop (right)]]

A '''motherboard''' (sometimes alternatively known as the '''mainboard''', '''system board''', '''planar board''' or '''logic board'''<ref name="Engadget">{{Cite web|url=http://www.engadget.com/2006/07/08/apple-sneaks-new-logic-board-into-whining-macbook-pros/|title=Apple sneaks new logic board into whining MacBook Pros|accessdate=2008-10-23|author=Paul Miller|format=2006|publisher=Engadget}}</ref>) is a [[printed circuit board]] (PCB) found in many modern [[computer]]s which holds many of the crucial components of the system, such as the [[central processing unit]] (CPU) and [[computer memory|memory]], and provides connectors for other peripherals.

''Motherboard'' specifically refers to a PCB with expansion capability. The term ''mainboard'' is applied to devices with a single board and no additional expansions or capability. In modern terms this would include controlling boards in televisions, washing machines and other [[embedded system]]s.

== History ==

Prior to the advent of the [[microprocessor]], a computer was usually built in a [[card-cage]] case or [[mainframe computer|mainframe]] with components connected by a [[backplane]] consisting of a set of slots themselves connected with wires; 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]], memory and [[peripherals]] were housed on individual printed circuit boards which 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, motherboards began to include single ICs (called [[Super I/O]] chips) capable of supporting a set of low-speed peripherals: [[Keyboard (computing)|keyboard]], [[Mouse (computing)|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 computer graphics|3D]] gaming and [[computer graphics]] typically retained only the graphics card as a separate component.

The early pioneers of motherboard manufacturing were [[Micronics]], [[Mylex]], [[American Megatrends|AMI]], DTK, [[Hauppauge Computer Works|Hauppauge]], [[Orchid Technology]], [[Elitegroup]], [[DFI]], and a number of Taiwan-based manufacturers.

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 ==
[[file:386DX40 MB Jaguar V.jpg|thumb|The Octek Jaguar V motherboard from 1993.<ref>{{cite web|url=http://redhill.net.au/b/b-93.html|title=Golden Oldies: 1993 mainboards|accessdate=2007-06-27}}</ref> This board has few onboard peripherals, as evidenced by the 6 slots provided for [[ISA bus|ISA]] cards and the lack of other built-in external interface connectors]]
[[file:Samsung galaxy s2 internal2.JPG|thumb|The motherboard of a [[Samsung Galaxy SII]]; almost all functions of the device are integrated into a very small board]]


A motherboard provides the electrical connections by which the other components of the system communicate. Unlike a backplane, it also connects the [[central processing unit]] and hosts other subsystems and devices.

A typical [[desktop computer]] has its [[microprocessor]], [[primary storage|main memory]], and other essential components connected to the motherboard. Other components such as [[external storage]], controllers for [[video card|video]] display and [[sound card|sound]], and [[peripheral]] devices may be attached to the 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, at a minimum:

* [[CPU socket|socket]]s (or slots) in which one or more [[microprocessor]]s may be installed. In the case of CPUs in [[Ball grid array|BGA]] packages, such as the [[VIA C3]], the CPU is directly soldered to the motherboard.{{cn|date=July 2012}}
* Slots into which the system's main memory is to be installed (typically in the form of [[DIMM]] modules containing [[Dynamic random access memory|DRAM]] chips)
* A [[chipset]] which forms an interface between the CPU's [[front-side bus]], main memory, and peripheral [[bus (computing)|bus]]es
* [[Non-volatile memory]] chips (usually [[Flash ROM]] in modern motherboards) containing the system's [[firmware]] or [[BIOS]]
* A [[clock generator]] which produces the system [[clock signal]] to synchronize the various components
* Slots for [[expansion card]]s (these interface to the system via the buses supported by the chipset)
* Power connectors, which receive electrical power from the [[computer power supply]] and distribute it to the CPU, chipset, main memory, and expansion cards. {{As of|2007}}, some [[graphics card]]s (e.g. [[GeForce 8]] and [[Radeon R600]]) require more power than the motherboard can provide, and thus dedicated connectors have been introduced to attach them directly to the power supply.<ref>http://www.techpowerup.com/articles/overclocking/psu/116</ref> Most [[disk drive]]s also connect to the power supply via dedicated connectors.{{cn|date=July 2012}}

Additionally, nearly all motherboards include logic and connectors to support commonly used input devices, such as [[PS/2 connector]]s for a [[computer mouse|mouse]] and keyboard. Early [[personal computer]]s 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 controller]]s and [[serial port]]s were provided as expansion cards.

Given the high [[thermal design power]] of high-speed computer CPUs and components, modern motherboards nearly always include [[heat sink]]s and mounting points for [[computer fan|fan]]s to dissipate excess heat.

=== CPU sockets ===

A [[CPU socket]] 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 computer]]s (laptops typically use surface mount 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 ===
[[file:Motherboard diagram.svg|thumb|Block diagram of a modern motherboard, which supports many on-board peripheral functions as well as several expansion slots]]

With the steadily declining costs and size of [[integrated circuit]]s, it is now possible to include support for many [[peripherals]] on the motherboard. By combining many functions on one [[Printed circuit board|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.

For example, the [[Elitegroup Computer Systems|ECS]] RS485M-M,<ref>{{cite web|url=http://www.ecs.com.tw/ECSWebSite/Products/ProductsDetail.aspx?DetailID=654&CategoryID=1&DetailName=Feature&MenuID=46&LanID=9|title=RS485M-M (V1.0)|accessdate=2007-06-27}}</ref> a typical modern budget motherboard for computers based on [[Advanced Micro Devices|AMD]] processors, has on-board support for a very large range of peripherals:

* [[Disk controller]]s for a [[floppy disk drive]], up to 2 [[AT Attachment|PATA]] drives, and up to 6 [[Serial ATA|SATA]] drives (including [[RAID#Standard RAID levels|RAID 0/1]] support)
* [[Integrated Graphics#Integrated graphics solutions|integrated]] graphics controller supporting [[2D computer graphics|2D]] and [[3D computer graphics|3D]] graphics, with [[Video Graphics Array|VGA]] and [[TV-out|TV]] output
* [[Sound card#Integrated sound on the PC|integrated sound card]] supporting 8-channel (7.1) audio and [[S/PDIF]] output
* [[Fast Ethernet]] [[Network card|network controller]] for 10/100 [[Megabit|Mbit]] networking
* [[Universal Serial Bus|USB 2.0]] controller supporting up to 12 USB ports
* [[Infrared Data Association|IrDA]] controller for infrared data communication (e.g. with an IrDA-enabled cellular phone or printer)
* Temperature, voltage, and fan-speed sensors that allow [[software]] to monitor the health of computer components

Expansion cards to support all of these functions would have cost hundreds of dollars even a decade ago; however, {{as of|2007|4|lc=on}} such highly integrated motherboards are available for as little as $30 in the US.

=== Peripheral card slots ===

A typical motherboard of 2009 will have a different number of connections depending on its standard.

A standard ATX motherboard will typically have one PCI-E 16x connection for a graphics card, two conventional PCI slots for various expansion cards, and one PCI-E 1x (which will eventually supersede [[Conventional PCI|PCI]]). A standard [[EATX]] motherboard will have one [[PCI-Express]] 16x connection for a graphics card, and a varying number of PCI and PCI-E 1x slots. It can sometimes also have a PCI-E 4x slot. (This varies between brands and models.)

Some motherboards have two PCI-E 16x slots, to allow more than 2 monitors without special hardware, or use a special graphics technology called [[Scalable Link Interface|SLI]] (for [[Nvidia]]) and [[ATI CrossFire|Crossfire]] (for [[ATI (brand)|ATI]]). These allow 2 graphics cards to be linked together, to allow better performance in intensive graphical computing tasks, such as gaming,video editing etc.

As of 2007, virtually all motherboards come with at least four [[USB]] ports on the rear, with at least 2 connections on the board internally for wiring additional front ports that may be built into the [[computer case]]. [[Ethernet]] is also included. This is a standard networking cable for connecting the computer to a [[computer network|network]] or a [[modem]]. A sound chip is always included on the motherboard, to allow sound output without the need for any extra [[electronic component|component]]s. This allows computers to be far more [[multimedia]]-based than before. Some motherboards contain video outputs on the back panel for integrated graphics solutions (either embedded in the motherboard, or combined with the microprocessor, such as the Intel HD Graphics). A separate card may still be used.

=== Temperature and reliability ===
[[file:MicroATX Motherboard with AMD Athlon Processor 2 Digon3.jpg|thumb|A microATX motherboard with some faulty capacitors]]
{{main|Computer cooling}}

Motherboards are generally [[air cooling|air cool]]ed with [[heat sink]]s often mounted on larger chips, such as the [[Northbridge (computing)|Northbridge]], in modern motherboards. Insufficient or improper cooling can cause damage to the internal components of the computer and cause it to [[crash (computing)|crash]]. [[Passive cooling]], or a single fan mounted on the [[power supply]], was sufficient for many desktop computer CPUs until the late 1990s; since then, most have required [[CPU fan]]s mounted on their [[heat sinks]], due to rising clock speeds and power consumption. Most motherboards have connectors for additional [[case fans]] as well. Newer motherboards have integrated temperature sensors to detect motherboard and CPU temperatures, and controllable fan connectors which the [[BIOS]] or [[operating system]] can use to regulate fan speed. Some computers (which typically have high-performance microprocessors, large amounts of [[RAM]], and high-performance [[video cards]]) use a [[water-cooling]] system instead of many fans.

Some [[small form factor]] computers and [[home theater PC]]s designed for quiet and energy-efficient operation boast fan-less designs. This typically requires the use of a low-power CPU, as well as careful layout of the motherboard and other [[Electronic component|component]]s to allow for heat sink placement.

A 2003 study found that some spurious computer crashes and general reliability issues, ranging from screen image distortions to [[I/O]] read/write errors, can be attributed not to [[software]] or peripheral [[personal computer hardware|hardware]] but to aging [[capacitor]]s on PC motherboards.<ref>''[[c't|c't Magazine]]'', vol. 21, pp. 216-221. 2003.</ref> Ultimately this was shown to be the result of a faulty electrolyte formulation,<ref>[http://web.archive.org/web/20030219071949/http://www.spectrum.ieee.org/WEBONLY/resource/feb03/ncap.html Yu-Tzu Chiu, Samuel K. Moore "Faults & Failures: Leaking Capacitors Muck up Motherboards" (2003-02-19) ''IEEE Spectrum'' accessed 2008-03-10]</ref> an issue termed [[capacitor plague]].

Motherboards use [[electrolytic capacitor]]s to filter the [[Direct current|DC]] power distributed around the board. These capacitors age at a temperature-dependent rate, as their water based [[electrolyte]]s slowly evaporate. This can lead to loss of capacitance and subsequent motherboard malfunctions due to [[voltage]] instabilities. While most capacitors are rated for 2000 hours of operation at {{convert|105|C|abbr=on}},<ref>[http://www.low-esr.com/endurance.asp Capacitor lifetime formula]</ref> their expected design life roughly doubles for every {{convert|10|C|abbr=on}} below this. At {{convert|45|C|abbr=on}} a lifetime of 15 years can be expected. This appears reasonable for a computer motherboard. However, many manufacturers have delivered substandard capacitors,<ref>Carey Holzman ''The healthy PC: preventive care and home remedies for your computer'' McGraw-Hill Professional, 2003 ISBN 0-07-222923-3 page 174</ref> which significantly reduce life expectancy. Inadequate case cooling and elevated temperatures easily exacerbate this problem. It is possible, but tedious and time-consuming, to find and replace failed capacitors on PC motherboards.

=== Form factor ===
{{main|Comparison of computer form factors}}

Motherboards are produced in a variety of sizes and shapes called [[computer form factor]], some of which are specific to individual [[computer manufacturer]]s. However, the motherboards used in IBM-compatible systems are designed to fit various [[computer case|case]] sizes. {{As of|2007}}, most [[desktop computer]] motherboards use the [[ATX]] standard form factor — even those found in [[Macintosh]] and [[Sun Microsystems|Sun]] computers, which have not been built from commodity components. A case's motherboard and PSU form factor must all match, though some smaller form factor motherboards of the same family will fit larger cases. For example, an ATX case will usually accommodate a [[microATX]] motherboard.

[[Laptop]] computers generally use highly integrated, miniaturized and customized motherboards. This is one of the reasons that laptop computers are difficult to upgrade and expensive to repair. Often the failure of one laptop component requires the replacement of the entire motherboard, which is usually more expensive than a desktop motherboard due to the large number of integrated components.

== Bootstrapping using the BIOS ==

Motherboards contain some [[non-volatile memory]] to initialize the system and load an [[operating system]] from some external peripheral device. Microcomputers such as the Apple II and IBM PC used [[Read-only memory|ROM]] chips, mounted in sockets on the motherboard. At power-up, the central processor would load its program counter with the address of the boot ROM and start executing ROM instructions. These instructions displayed system information on the screen, ran memory checks, and then loaded an operating system from an external or peripheral device (disk drive). If none was available, then the computer would perform tasks from other memory stores or display an error message, depending on the model and design of the computer and version of the BIOS.

Most modern motherboard designs use a [[BIOS]], stored in an [[EEPROM]] chip soldered or socketed to the motherboard, to [[bootstrap]] an [[operating system]]. When power is first applied to the motherboard, the BIOS firmware tests and configures memory, circuitry, and peripherals. This [[Power-On Self Test]] (POST) may include testing some of the following things:

* [[Video adapter]]
* Cards inserted into slots, such as [[conventional PCI]]
* [[Floppy drive]]
* [[Thermistor]]s, [[voltage]]s, and fan speeds for [[hardware monitoring]]
* [[CMOS]] used to store [[BIOS setup]] configuration
* [[Keyboard (computing)|keyboard]] and [[computer mouse|mouse]]
* [[Computer network|network]] controller
* Optical drives: [[CD-ROM]] or [[DVD-ROM]]
* [[SCSI]] hard drive
* [[Integrated Drive Electronics|IDE]], [[EIDE]], or [[SATA]] [[hard disk]]
* Security devices, such as a [[fingerprint reader]] or the state of a latch switch to detect intrusion
* [[USB]] devices, such as a memory storage device

On recent motherboards, the BIOS may also patch the central processor microcode if the BIOS detects that the installed CPU is one in for which [[errata]] has been published.

== See also ==

* [[Accelerated Graphics Port]]
* [[Computer case screws]]
* [[Daughterboard]]
* [[List of computer hardware manufacturers]]
* [[Offboard]]
* [[Overclocking]]
* [[Single-board computer]]
* [[Switched-mode power supply applications]]

== References ==

{{refs}}

== External links ==
{{commonscat|Computer motherboards}}

* {{dmoz|Computers/Hardware/Components/Motherboards|Motherboards}}
* [http://www.wimsbios.com/biosupdates.jsp List of motherboard manufacturers and links to BIOS updates]
* [http://www.pcreview.co.uk/articles/Hardware/What_is_a_Motherboard/ What is a motherboard?]
* [http://www.hardcoreware.net/reviews/review-335-1.htm The Making of a Motherboard: ECS Factory Tour]
* [http://www.hardcoreware.net/reviews/review-217-1.htm The Making of a Motherboard: Gigabyte Factory Tour]
* [http://www.formfactors.org/developer/specs/A2928604-005.pdf Front Panel I/O Connectivity Design Guide] - v1.3 (pdf file) (February 2005)

{{Basic computer components}}

[[Category:IBM PC compatibles]]
[[Category:Motherboard]]

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Revision as of 12:54, 18 September 2012

a board that is a mother

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