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:
Additionally, nearly all motherboards include logic and connectors to support commonly used input devices, such as USB for mouse devices and keyboards. 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.
Form factorEdit
Motherboards are produced in a variety of sizes and shape 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 2005, most desktop computer motherboards use the ATX standard form factor even those found in Macintosh and Sun computers, which have not been built from commodity components. A case's motherboard and power 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 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
CPU socketsEdit
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 CPUs], particularly those based on the Intel x86 architecture. A CPU socket type and motherboard chipset must support the CPU series and speed.
Integrated peripheralsEdit
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 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.
Peripheral card slotsEdit
A typical motherboard will have a different number of connections depending on its standard and form factor.
A standard, modern ATX motherboard will typically have two or three PCI-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 superseded PCI]. A standard EATX 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 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.
In newer motherboards, the M.2 slots are for SSD and/or Wireless network interface controller.
Temperature and reliabilityEdit
A motherboard of a Vaio E series laptop [right]
A microATX motherboard with some faulty capacitors
Motherboards are generally air cooled with heat sinks often mounted on larger chips 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 heat sinks, due to rising clock speeds and power consumption. Most motherboards have connectors for additional computer fans and 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.[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 a 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.
Modern 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 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.
In Desktop PCs and notebook computers, the motherboard cooling and monitoring solutions are usually based on Super I/O or Embedded Controller.