Dell Precision T3600 System Motherboard, used in professional CAD Workstations. Manufactured in 2012
Amotherboard (also calledmainboard,maincircuit board,MB,mobo,base board,system board, or, inApple computers,logic board) is the mainprinted circuit board (PCB) in general-purposecomputers and other expandable systems. It holds and allows communication between many of the crucial electronic components of a system, such as thecentral processing unit (CPU) andmemory, and provides connectors for otherperipherals. Unlike abackplane, a motherboard usually contains significant sub-systems, such as the central processor, thechipset'sinput/output and memory controllers,interface connectors, and other components integrated for general use.
Motherboard means specifically a PCB with expansion capabilities. As the name suggests, this board is often referred to as themother of all components attached to it, which often include peripherals, interface cards, anddaughterboards:sound cards,video cards,network cards,host bus adapters,TV tuner cards,IEEE 1394 cards, and a variety of other custom components.
Similarly, the termmainboard describes a device with a single board and no additional expansions or capability, such as controlling boards in laser printers,television sets, washing machines,mobile phones, and otherembedded systems with limited expansion abilities.
Motherboard for a personal desktop computer from the 1990s; showing the typical components and interfaces which are found on a motherboard. This model follows the BabyAT (form factor), used in many desktop PCs of the time.
Prior to the invention of themicroprocessor, theCPU of adigital computer consisted of multiple circuit boards in a card-cage case with components connected by abackplane containing a set of interconnected sockets into which thecircuit boards are plugged. In very old designs, copper wires were the discrete connections between card connector pins, but printed circuit boards soon became the standard practice. Thecentral processing unit (CPU),memory, andperipherals were housed on individually printed circuit boards, which were plugged into the backplane.
In older microprocessor-based systems, the CPU and some support circuitry would fit on a single CPU board, with memory and peripherals on additional boards, all plugged into the backplane. The ubiquitousS-100 bus of the 1970s is an example of this type of backplane system.
The most popular computers of the 1980s such as theApple II andIBM PC had published schematic diagrams and other documentation which permitted rapidreverse 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 calledSuper I/O chips) capable of supporting a set of low-speed peripherals:PS/2keyboard andmouse,floppy disk drive,serial ports, andparallel ports. By the late 1990s, many personal computer motherboards included consumer-grade embedded audio, video, storage, and networking functions without the need for anyexpansion cards at all; higher-end systems for3D gaming andcomputer 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 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 thetablet computer and thenetbook). Memory, processors, network controllers, power source, and storage would be integrated into some systems.
The Octek Jaguar V motherboard from 1993.[1] This board has few onboard peripherals, as evidenced by the 6 slots provided forISA cards and the lack of other built-in external interface connectors. Note the largeAT keyboard connector at the back right is its only peripheral interface.The motherboard of aSamsung 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 typicaldesktop computer has itsmicroprocessor,main memory, and other essential components connected to the motherboard. Other components such asexternal storage, controllers forvideo display andsound, 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 supportingchipset, which provides the supporting interfaces between the CPU and the variousbuses and external components. This chipset determines, to an extent, the features and capabilities of the motherboard.
Memory slots into which the system's main memory is to be installed, typically in the form ofDIMM modules containingDRAM chips. Can beDDR3,DDR4,DDR5, or onboardLPDDRx.
Thechipset which forms an interface between theCPU,main memory, and peripheral buses
Slots forexpansion cards (the interface to the system via the buses supported by the chipset)
Power connectors, which receive electrical power from the computerpower supply and distribute it to the CPU, chipset, main memory, and expansion cards. As of 2007[update], somegraphics cards (e.g.GeForce 8 andRadeon R600) require more power than the motherboard can provide, and thus dedicated connectors have been introduced to attach them directly to the power supply.[3]
Connectors for hard disk drives, optical disc drives, or solid-state drives, typicallySATA andNVMe
Additionally, nearly all motherboards include logic and connectors to support commonly used input devices, such asUSB formouse devices andkeyboards. Earlypersonal computers such as theApple II andIBM PC include 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 theIBM PCjr. Additional peripherals such asdisk controllers andserial ports were provided as expansion cards.
Given the highthermal design power of high-speed computer CPUs and components, modern motherboards nearly always includeheat sinks and mounting points forfans to dissipate excess heat.
Motherboards are produced in a variety of sizes and shapes calledform factors, some of which are specific to individual computer manufacturers. However, the motherboards used in IBM-compatible systems are designed to fit variouscase sizes. As of 2024[update], mostdesktop computer motherboards use theATX standard form factor — even those found inMacintosh andSun computers, which have not been built from commodity components. A case's motherboard andpower supply unit (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 amicroATX 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.
ACPU 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 andserver computers (laptops typically use surface mount CPUs), particularly those based on theIntel x86 architecture. A CPU socket type and motherboard chipset must support the CPU series and speed.
Block diagram of an early 2000s motherboard, which supports many on-board peripheral functions as well as several expansion slots
With the steadily declining costs and size ofintegrated circuits, it is now possible to include support for manyperipherals on the motherboard. By combining many functions on onePCB, the physical size and total cost of the system may be reduced; highly integrated motherboards are thus especially popular insmall form factor and budget computers. Theintegrated peripherals may also be calledonboard devices.
A typical motherboard will have a different number of connections depending on its standard andform factor.
A standard, modern ATX motherboard will typically have two or threePCI-Express x16 connection for a graphics card, one or two legacy PCI slots for various expansion cards, and one or two PCI-E x1 (which has supersededPCI). A standardEATX motherboard will have two to four PCI-E x16 connection for graphics cards, and a varying number of PCI and PCI-E x1 slots. It can sometimes also have a PCI-E x4 slot (will vary between brands and models).
Some motherboards have two or more PCI-E x16 slots, to allow more than 2 monitors without special hardware, or use a special graphics technology calledSLI (forNvidia) andCrossfire (forAMD). 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.
Motherboards are generallyair cooled withheat sinks often mounted on larger chips in modern motherboards.[4] Insufficient or improper cooling can cause damage to the internal components of the computer, or cause it tocrash.Passive cooling, or a single fan mounted on thepower supply, was sufficient for many desktop computer CPU's until the late 1990s; since then, most have requiredCPU fans mounted onheat sinks, due to rising clock speeds and power consumption. Most motherboards have connectors for additionalcomputer fans and integrated temperature sensors to detect motherboard and CPU temperatures and controllable fan connectors which theBIOS oroperating system can use to regulate fan speed.[5] Alternatively computers can use awater cooling system instead of many fans.
Somesmall form factor computers andhome 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 a careful layout of the motherboard and othercomponents to allow for heat sink placement.
A 2003 study found that some spurious computer crashes and general reliability issues, ranging from screen image distortions toI/O read/write errors, can be attributed not tosoftware or peripheralhardware but to agingcapacitors on PC motherboards.[6] Ultimately this was shown to be the result of a faulty electrolyte formulation,[7] an issue termedcapacitor plague.
Modern motherboards useelectrolytic capacitors to filter theDC power distributed around the board. These capacitors age at a temperature-dependent rate, as their water basedelectrolytes slowly evaporate. This can lead to loss of capacitance and subsequent motherboard malfunctions due tovoltage instabilities. While most capacitors are rated for 2000 hours of operation at 105 °C (221 °F),[8] 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,[9] which significantly reduce life expectancy. Inadequate case cooling and elevated temperatures around the 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, usesolid 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).[10] 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.
In desktop PCs and notebook computers, the motherboard cooling and monitoring solutions are usually based on asuper I/O chip or anembedded controller.
Microcomputers such as theApple II and IBM PC used ROM chips mounted in sockets on the motherboard. At power-up, thecentral processor unit would load itsprogram counter with the address of the Boot ROM and start executing instructions from the Boot ROM. These instructions initialized and tested the system hardware, displayed system information on the screen, performedRAM checks, and then attempts to boot an operating system from a peripheral device. If no peripheral device containing an operating system was available, then the computer would perform tasks from other ROM stores or display an error message, depending on the model and design of the computer. For example, both the Apple II and the original IBM PC hadCassette BASIC (ROM BASIC) and would start that if no operating system could be loaded from the floppy disk or hard disk.
The boot firmware in modernIBM PC compatible motherboard designs contains either aBIOS, as did the boot ROM on the original IBM PC, orUEFI. UEFI is a successor to BIOS that became popular after Microsoft began requiring it for a system to be certified to runWindows 8.[12][13]
When the computer is powered on, the boot firmware tests and configures memory, circuitry, and peripherals. ThisPower-On Self Test (POST) may include testing some of the following things:
^"Windows Hardware Certification Requirements for Client and Server Systems". Microsoft. January 2013.Archived from the original on November 5, 2021. RetrievedJuly 3, 2020.System.Fundamentals.Firmware.CS.UEFISecureBoot.ConnectedStandby ... Platforms shall be UEFI Class Three (see UEFI Industry Group, Evaluating UEFI using Commercially Available Platforms and Solutions, version 0.3, for a definition) with no Compatibility Support Module installed or installable. BIOS emulation and legacy PC/AT boot must be disabled.
