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A motherboard (sometimes alternatively known as the mainboard, system board, baseboard, planar board or logic board,[1] or colloquially, a mobo) is the main printed circuit board (PCB) found in general purpose microcomputers and other expandable systems. It holds and allows communication between many of the crucial electronic components of a system, such as the central processing unit (CPU) and memory, and provides connectors for other peripherals. Unlike a backplane, a motherboard usually contains significant sub-systems such as the central processor, the chipset's input/output and memory controllers, interface connectors, and other components integrated for general purpose use. Motherboard
Motherboard
specifically refers to a PCB with expansion capability and as the name suggests, this board is often referred to as the "mother" of all components attached to it, which often include peripherals, interface cards, and daughtercards: sound cards, video cards, network cards, hard drives, or other forms of persistent storage; TV tuner cards, cards providing extra USB
USB
or FireWire slots and a variety of other custom components. Similarly, the term mainboard is applied to devices with a single board and no additional expansions or capability, such as controlling boards in laser printers, televisions, washing machines and other embedded systems with limited expansion abilities.

Contents

1 History 2 Design

2.1 Form factor 2.2 CPU sockets 2.3 Integrated peripherals 2.4 Peripheral
Peripheral
card slots 2.5 Temperature
Temperature
and reliability 2.6 Air pollution and reliability

3 Bootstrapping using the Basic Input/Output System 4 See also 5 References 6 External links

History[edit] 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, copper wires were the discrete connections between card connector pins, but printed circuit boards soon became the standard practice. The Central Processing Unit
Central Processing Unit
(CPU), memory, and peripherals were housed on individual printed circuit boards, which were plugged into the backplane. The ubiquitous S-100 bus
S-100 bus
of the 1970s is an example of this type of backplane system. The most popular computers of the 1980s such as the Apple II
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. During the late 1980s and early 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
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 included consumer grade embedded 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. Business PCs, workstations, and servers were more likely to need expansion cards, either for more robust functions, or for higher speeds; those systems often had fewer embedded components. Laptop
Laptop
and notebook computers that were developed in the 1990s integrated the most common peripherals. This even included motherboards with no upgradeable components, a trend that would continue as smaller systems were introduced after the turn of the century (like the tablet computer and the netbook). Memory, processors, network controllers, power source, and storage would be integrated into some systems. Design[edit]

The Octek Jaguar V motherboard from 1993.[2] This board has few onboard peripherals, as evidenced by the 6 slots provided for ISA cards and the lack of other built-in external interface connectors. Note the large AT keyboard
AT keyboard
connector at the back right is its only peripheral interface.

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 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 motherboard as plug-in cards or via cables; in modern microcomputers 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 (or slots) in which one or more microprocessors may be installed. In the case of CPUs in ball grid array packages, such as the VIA C3, the CPU is directly soldered to the motherboard.[3] Slots into which the system's main memory is to be installed (typically in the form of DIMM
DIMM
modules containing DRAM chips) A chipset which forms an interface between the CPU's front-side bus, main memory, and peripheral buses Non-volatile memory chips (usually Flash ROM
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 cards (the 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[update], some graphics cards (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.[4] Connectors for hard drives, typically SATA
SATA
only. Disk drives also connect to the power supply.

Additionally, nearly all motherboards include logic and connectors to support commonly used input devices, such as USB
USB
for mouse devices and keyboards. Early personal computers such as the Apple II
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
Apple II
and rarely on IBM-compatible computers such as the IBM PC
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. Form factor[edit] Main article: 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 manufacturers. However, the motherboards used in IBM-compatible systems are designed to fit various case sizes. As of 2007[update], most desktop computer motherboards use the ATX
ATX
standard form factor — even those found in Macintosh
Macintosh
and 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
ATX
case will usually accommodate a micro ATX
ATX
motherboard. Laptop
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 and their custom shape and size. The motherboardlayout for laptops depends on the laptop case. CPU sockets[edit] A CPU socket
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
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 CPUs), particularly those based on the Intel x86
Intel x86
architecture. A CPU socket
CPU socket
type and motherboard chipset must support the CPU series and speed. Integrated peripherals[edit]

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 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.

Disk controllers for a floppy disk drive, up to 2 PATA drives, and up to 6 SATA
SATA
drives (including RAID 0/1 support) integrated graphics controller supporting 2D and 3D graphics, with VGA and TV output integrated sound card supporting 8-channel (7.1) audio and S/PDIF output Fast Ethernet
Fast Ethernet
network controller for 10/100 Mbit networking USB
USB
2.0 controller supporting up to 12 USB
USB
ports 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.

Peripheral
Peripheral
card slots[edit] A typical motherboard will have a different number of connections depending on its standard and form factor. A standard, modern ATX
ATX
motherboard will typically have two or three PCI-Express
PCI-Express
16x connection for a graphics card, one or two legacy PCI slots for various expansion cards, and one or two PCI-E 1x (which has superseded PCI). A standard E ATX
ATX
motherboard will have two to four PCI-E 16x connection for graphics cards, and a varying number of PCI and PCI-E 1x slots. It can sometimes also have a PCI-E 4x slot (will vary between brands and models). Some motherboards have two or more PCI-E 16x slots, to allow more than 2 monitors without special hardware, or use a special graphics technology called SLI (for Nvidia) and Crossfire (for AMD). These allow 2 to 4 graphics cards to be linked together, to allow better performance in intensive graphical computing tasks, such as gaming, video editing, etc. Temperature
Temperature
and reliability[edit]

A motherboard of a Vaio E series laptop (right)

A micro ATX
ATX
motherboard with some faulty capacitors

Main article: Computer
Computer
cooling Motherboards are generally air cooled with heat sinks often mounted on larger chips, such as the Northbridge, in modern motherboards.[5] Insufficient or improper cooling can cause damage to the internal components of the computer, or cause it to crash. Passive cooling, or a single fan mounted on the power supply, was sufficient for many desktop computer CPU's until the late 1990s; since then, most have required CPU fans mounted on their heat sinks, due to rising clock speeds and power consumption. Most motherboards have connectors for additional case fans and integrated temperature sensors to detect motherboard and CPU temperatures and controllable fan connectors which the BIOS
BIOS
or operating system can use to regulate fan speed.[6] Alternatively computers can use a water cooling system instead of many fans. Some small form factor computers and home theater PCs 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 components 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 hardware but to aging capacitors on PC motherboards.[7] Ultimately this was shown to be the result of a faulty electrolyte formulation,[8] an issue termed capacitor plague. Standard motherboards use electrolytic capacitors to filter the DC power distributed around the board. These capacitors age at a temperature-dependent rate, as their water based electrolytes 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 105 °C (221 °F),[9] their expected design life roughly doubles for every 10 °C (18 °F) below this. At 65 °C (149 °F) a lifetime of 3 to 4 years can be expected. However, many manufacturers deliver substandard capacitors,[10] which significantly reduce life expectancy. Inadequate case cooling and elevated temperatures around the CPU socket
CPU socket
exacerbate this problem. With top blowers, the motherboard components can be kept under 95 °C (203 °F), effectively doubling the motherboard lifetime. Mid-range and high-end motherboards on the other hand use solid capacitors exclusively. For every 10 °C less, their average lifespan is multiplied approximately by three, resulting in a 6-times higher lifetime expectancy at 65 °C (149 °F).[11] These capacitors may be rated for 5000, 10000 or 12000 hours of operation at 105 °C (221 °F), extending the projected lifetime in comparison with standard solid capacitors. Air pollution and reliability[edit] High rates of motherboard failures in China and India appear to be due to "sulfurous air pollution produced by coal" that's burned to generate electricity. Air pollution corrodes the circuitry, according to Intel
Intel
researchers.[12] Bootstrapping using the Basic Input/Output System[edit] Motherboards contain some non-volatile memory to initialize the system and load some startup software, usually an operating system, from some external peripheral device. Microcomputers such as the Apple II
Apple II
and IBM PC
IBM PC
used 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 instructions from the ROM. These instructions initialized and tested the system hardware, displayed system information on the screen, performed RAM checks, and then loaded an initial program from an external or peripheral device. 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 the ROM version. For example, both the Apple II
Apple II
and the original IBM PC
IBM PC
had Microsoft Cassette BASIC in ROM and would start that if no program could be loaded from disk. Most modern motherboard designs use a BIOS, stored in an EEPROM
EEPROM
chip soldered to or socketed on the motherboard, to booting an operating system. Non-operating system boot programs are still supported on modern IBM PC-descended machines, but nowadays it is assumed that the boot program will be a complex operating system such as Microsoft Windows or Linux. When power is first supplied to the motherboard, the BIOS
BIOS
firmware tests and configures memory, circuitry, and peripherals. This Power-On Self Test
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 Temperatures, voltages, and fan speeds for hardware monitoring CMOS memory
CMOS memory
used to store BIOS
BIOS
setup configuration Keyboard and Mouse Network controller Optical drives: CD-ROM
CD-ROM
or DVD-ROM SCSI
SCSI
hard drive IDE, EIDE, or Serial ATA
Serial ATA
Hard disk drive Security devices, such as a fingerprint reader or the state of a latching switch to detect intrusion USB
USB
devices, such as a memory storage device

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

Accelerated Graphics Port Computer case
Computer case
screws CMOS battery Daughterboard List of computer hardware manufacturers Memory Reference Code – the part of the BIOS
BIOS
which handles memory timings on Intel
Intel
motherboards Overclocking Single-board computer Switched-mode power supply applications Symmetric multiprocessing

References[edit]

^ Miller, Paul (2006-07-08). "Apple sneaks new logic board into whining MacBook Pros". Engadget. Archived from the original on 2013-10-04. Retrieved 2013-10-02.  ^ "Golden Oldies: 1993 mainboards". Archived from the original on 2007-05-13. Retrieved 2007-06-27.  ^ "CPU Socket Types Explained: From Socket 5 To BGA [MakeUseOf Explains]". 2013-01-25. Archived from the original on 2015-04-07. Retrieved 2015-04-12.  ^ W1zzard (2005-04-06). "Pinout of the PCI-Express
PCI-Express
Power Connector". techPowerUp. Archived from the original on 2013-10-04. Retrieved 2013-10-02.  ^ Karbo, Michael. "The CPU and the motherboard". Karbos Guide. Archived from the original on 27 April 2015. Retrieved 21 June 2015.  ^ "Temperatures". Intel® Visual BIOS
BIOS
Wiki. Google. Archived from the original on 21 June 2015. Retrieved 21 June 2015.  ^ c't Magazine, vol. 21, pp. 216-221. 2003. ^ Chiu, Yu-Tzu; Moore, Samuel K. (2003-01-31). "Faults & Failures: Leaking Capacitors Muck up Motherboards". IEEE Spectrum. Archived from the original on 2003-02-19. Retrieved 2013-10-02.  ^ " Capacitor
Capacitor
lifetime formula". Low-esr.com. Archived from the original on 2013-09-15. Retrieved 2013-10-02.  ^ Carey Holzman The healthy PC: preventive care and home remedies for your computer McGraw-Hill Professional, 2003 ISBN 0-07-222923-3 page 174 ^ "-- GIGABYTE --Geeks Column of the Week - All Solid Capacitor". www.gigabyte.com. Archived from the original on 2017-03-27. Retrieved 2017-05-06.  ^ "Scientists studying pollution damage to computers". Missoulian. 2013-10-27. Archived from the original on 2013-10-28. Retrieved 2013-10-27. 

External links[edit]

Wikimedia Commons has media related to Computer
Computer
motherboards.

Motherboard
Motherboard
Form Factors - Silverstone Article Motherboards at Curlie (based on DMOZ) List of motherboard manufacturers and links to BIOS
BIOS
updates What is a motherboard? The Making of a Motherboard: ECS Factory Tour The Making of a Motherboard: Gigabyte Factory Tour Front Panel I/O
I/O
Connectivity Design Guide - v1.3 (pdf file)

v t e

Basic computer components

Input devices

Keyboard Image scanner Microphone Pointing device

Graphics tablet Joystick Light pen Mouse

Optical

Pointing stick Touchpad Touchscreen Trackball

Webcam

Softcam

Refreshable braille display

Output devices

Monitor Refreshable braille display Printer Speakers Plotter

Removable data storage

Optical disc

CD DVD Blu-ray

Disk pack Floppy disk Memory card USB
USB
flash drive

Computer
Computer
case

Central processing unit
Central processing unit
(CPU) HDD / SSD / SSHD Motherboard Network interface controller Power supply Random-access memory
Random-access memory
(RAM) Sound card Video card Fax modem Expansion card

Ports

Ethernet FireWire (IEEE 1394) Parallel port Serial port PS/2 port USB Thunderbolt HDMI
HDMI
/ DVI / VG

.