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A motherboard is the central printed circuit board (PCB) in some complex electronic systems, such as modern personal computers. The motherboard is sometimes alternatively known as the mainboard, system board, or, on Apple computers, the logic board.It is also sometimes casually shortened to mobo.

Overview

An Acer E360 motherboard made by Foxconn, from 2005, with a large number of integrated peripherals. This board’s nForce3 chipset lacks a traditional northbridge.

Most computer motherboards produced today are designed for IBM-compatible computers, which currently account for around 90% of global PC sales. A motherboard, like a backplane, provides the electrical connections by which the other components of the system communicate, but unlike a backplane, it also hosts the central processing unit, and other subsystems and devices.

Motherboards are also used in many other electronics devices.

A typical desktop computer has its microprocessor, main memory, and other essential components on 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, although 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:

• sockets (or slots) in which one or more microprocessors are installed
• slots into which the system’s main memory is installed (typically in the form of 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 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 (these interface to the system via the buses supported by the chipset)
• power connectors flickers, which receive electrical power from the computer power supply and distribute it to the CPU, chipset, main memory, and expansion cards.

The Octek Jaguar V motherboard from 1993.This board has 6 ISA slots but few onboard peripherals, as evidenced by the lack of external connectors.

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 heatsinks and mounting points for fans to dissipate excess heat.

CPU sockets

Integrated peripherals

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.

For example, the ECS RS485M-M, a typical modern budget motherboard for computers based on AMD processors, has on-board support for a very large range of peripherals:

• disk controllers for a floppy disk drive, up to 2 PATA drives, and up to 6 SATA drives (including RAID 0/1 support)
• integrated ATI Radeon 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 network controller for 10/100 Mbit networking
• USB 2.0 controller supporting up to 12 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

Expansion cards to support all of these functions would have cost hundreds of dollars even a decade ago, however as of April 2007^[update] such highly-integrated motherboards are available for as little as $30 in the USA.

Peripheral card slots

A typical motherboard of 2007 will have a different number of connections depending on its standard. A standard ATX motherboard will typically have 1x PCI-E 16x connection for a graphics card, 2x PCI slots for various expansion cards and 1x PCI-E 1x which will eventually supersede PCI.

A standard Super ATX motherboard will have 1x PCI-E 16x connection for a graphics card. It will also have 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 2x PCI-E 16x slots, to allow more than 2 monitors without special hardware or to allow use of a special graphics technology called SLI (for Nvidia) and Crossfire (for ATI). These allow 2 graphics cards to be linked together, to allow better performance in intensive graphical computing tasks, such as gaming and video-editing.

As of 2007^[update], virtually all motherboards come with at least 4x USB ports on the rear, with at least 2 connections on the board internally for wiring additional front ports that are built into the computer’s case. Ethernet is also included now. This is a standard networking cable for connecting the computer to a network or a modem. A sound chip is always included on the motherboard, to allow sound to be output without the need for any extra components. This allows computers to be far more multimedia-based than before. Cheaper machines now often have their graphics chip built into the motherboard rather than a separate card.

Temperature and reliability

Motherboards are generally air cooled with heat sinks often mounted on larger chips, such as the northbridge, in modern motherboards. If the motherboard is not cooled properly, then this can cause its computer to 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 fans mounted on their heatsinks, 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 higher-powered computers (which typically have high-performance processors and large amounts of RAM, as well as high-performance video cards) 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. Ultimately this was shown to be the result of a faulty electrolyte formulation.

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, their expected design life roughly doubles for every 10 °C below this. At 45 °C a lifetime of 15 years can be expected. This appears reasonable for a computer motherboard, however many manufacturers have delivered substandard capacitors,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; it is less expensive to buy a new motherboard than to pay for such a repair.

Form factor

microATX form factor motherboard

Motherboards are produced in a variety of sizes and shapes (”form factors”), some of which are specific to individual computer manufacturers. However, the motherboards used in IBM-compatible commodity computers have been standardized to fit various case sizes. As of 2007^[update], most desktop computer motherboards use one of these standard form factors—even those found in Macintosh and Sun computers which have not traditionally been built from commodity components.

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.

Nvidia SLI and ATI Crossfire

Nvidia SLI and ATI Crossfire technology allows 2 or more of the same series graphics cards to be linked together to allow a faster graphics experience. Almost all medium to high end Nvidia cards and most high end ATI cards support the technology.

They both require compatible motherboards. There is an obvious need for 2x PCI-E 16x slots to allow 2 cards to be inserted into the computer. The same function can be achieved in 650i motherboards by NVIDIA, with a pair of x8 slots. Originally, tri-Crossfire was achieved at 8x speeds with 2 16x slots and 1 8x slot albeit at a slower speed. ATI opened the technology up to Intel in 2006 and such all new Intel chipsets support Crossfire.

SLI is a little more proprietary in its needs. It requires a motherboard with Nvidia’s own NForce chipset series to allow it to run (exception: Intel X58 chipset).

It is important to note that SLI and Crossfire will not usually scale to 2x the performance of a single card when using a dual setup. They also do not double the effective amount of VRAM or memory bandwidth.

History

Prior to the advent of the microprocessor, a computer was usually built in a card-cage case or 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 backplane.

During the late 1980s and 1990s, it became economical to move an increasing number of peripheral functions onto the motherboard (see above). 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, mouse, floppy disk drive, serial ports, and parallel ports. As of the late 1990s, many personal computer motherboards support 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 retain only the graphics card as a separate component.

The early pioneers of motherboard manufacturing were Micronics, Mylex, AMI, DTK, Hauppauge, Orchid Technology, Elitegroup, DFI, and a number of Taiwan-based manufacturers.

Popular personal 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.

The term mainboard is archaically applied to devices with a single board and no additional expansions or capability. In modern terms this would include embedded systems, and controlling boards in televisions, washing machines etc. A motherboard specifically refers to a printed circuit with the capability to add/extend its performance/capabailities with the addition of “daughterboards”.

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 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, displaying system information on the screen and running memory checks, which would in turn start loading memory from an external or peripheral device (disk drive). If none is available, then the computer can 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 to the motherboard, to bootstrap the motherboard. (Socketed BIOS chips are widely used, also.) By booting the motherboard, the memory, circuitry, and peripherals are tested and configured. This process is known as a computer Power-On Self Test (POST) and may include testing some of the following devices:

• floppy drive
• network controller
• CD-ROM drive
• DVD-ROM drive
• SCSI hard drive
• IDE, EIDE, or SATA hard drive
• External USB memory storage device

Any of the above devices can be stored with machine code instructions to load an operating system or a program.

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The top cover has been removed to show the internals of a computer Power supply Unit.

A power supply unit (PSU) is the component that supplies power to a computer. More specifically, a power supply is typically designed to convert 100-120 V (North America and Japan) or 220-240 V (New Zealand, Europe, South America, Africa, Asia and Australia) AC power from the mains to usable low-voltage DC power for the internal components of the computer. Some power supplies have a switch to change between 230 V and 115 V. Other models have automatic sensors that switch input voltage automatically, or are able to accept any voltage between those limits.

The most common computer power supplies are built to conform with the ATX form factor. The most recent specification of the ATX standard PSU as of mid-2008 is version 2.31. This enables different power supplies to be interchangeable with different components inside the computer. ATX power supplies also are designed to turn on and off using a signal from the motherboard, and provide support for modern functions such as the standby mode available in many computers.

Passive heat sink cooling

Passive heatsink fitted on a Intel GMA graphics chip

This involves attaching a block of machined metal to the part that needs cooling. An adhesive may be used, or more commonly for a personal computer CPU, a clamp is used to affix the heat sink right over the chip, with a thermally conductive pad or gel spread in-between. This block usually has fins and ridges to increase its surface area. The heat conductivity of metal is much better than that of air, and its ability to radiate heat is better than that of the component part it is protecting (usually an integrated circuit or CPU). Until recently, fan cooled aluminium heat sinks were the norm for desktop computers. Today many heat sinks feature copper base-plates or are entirely made of copper, and mount fans of considerable size and power.

Heat sinks tend to get less effective with time due to the build up of dust between their metal fins, which reduces the efficiency with which the heat sink transfers heat to the ambient air. Dust build up is commonly countered with canned air, which is used to blow away the dust along with any other unwanted excess material.

Passive heat sinks are commonly found on older CPUs, parts that do not get very hot (such as the chipset), and low-power computers.

Active heat sink cooling

This uses the same principle as a passive heat sink cooler, with the only difference being that a fan is directed to blow over or through the heat sink. This results in more air being blown through the heat sink, increasing the rate at which the heat sink can exchange heat with the ambient air. Active heat sinks are the primary method of cooling a modern day processor or graphics card.

The buildup of dust is greatly increased with active heat sink cooling as the fan is continually taking in the dust present in the surrounding air. As a result, dust removal procedures need to be exercised much more frequently than with passive heat sink methods.

Peltier cooling or thermoelectric cooling

In 1821 T. J. Seebeck discovered that different metals, connected at two different junctions, will develop a micro-voltage if the two junctions are held at different temperatures. This effect is known as the “Seebeck effect”; it is the basic theory behind the TEC (thermoelectric cooling).

In 1834 Jean Peltier discovered the inverse of the Seebeck effect, now known as the “Peltier effect”. He found that applying a voltage to a thermocouple creates a temperature differential between two sides. This results in an effective, albeit extremely inefficient heat pump.

Modern TECs use several stacked units each composed of dozens or hundreds of thermocouples laid out next to each other, which allows for a substantial amount of heat transfer. A combination of bismuth and telluride is most commonly used for thermocouples.

Since TECs are active heat pumps, they are capable of cooling PC components below ambient temperatures, which is impossible with common radiator cooled water cooling systems and heatpipe HSFs.

Heatsink n Fan     Watecooling reservoir   Watercooling System

Water cooling

DIY Watercooling setup showing 12v pump, CPU Waterblock and the typical application of a T-Line.

While originally limited to mainframe computers, computer watercooling has become a practice largely associated with overclocking in the form of either manufactured “kits” or in the form of DIY setups assembled from individually gathered parts. Lately watercooling has seen increasing use in pre-assembled desktop computers. Water cooling can extract more heat from the cooled parts, which makes it suitable for overclocking, and opposed to air cooling it is less influenced by the ambient temperature. One of its disadvantages is the potential for a coolant leak, which can damage electronic components. An advantage is that a water cooling system is not limited to one component, so it can cool the CPU, GPU and other components at the same time. Another advantage to water cooling is the low noise-level output it provides when compared to that of fan cooling, which can become loud especially when using a higher clock rate processor.

Heat pipe

A heat pipe is a hollow tube containing a heat transfer liquid. As the liquid evaporates, it carries heat to the cool end, where it condenses and then returns to the hot end (under capillary action). Heat pipes thus have a much higher effective thermal conductivity than solid materials. For use in computers, the heat sink on the CPU is attached to a larger radiator heat sink. Both heat sinks are hollow as is the attachment between them, creating one large heat pipe that transfers heat from the CPU to the radiator, which is then cooled using some conventional method. This method is expensive and usually used when space is tight (as in small form-factor PCs), or absolute quiet is needed (such as in computers used in audio production studios during live recording).

Phase-change cooling

Phase-change cooling is an extremely effective way to cool the processor. A vapor compression phase-change cooler is a unit which usually sits underneath the PC, with a tube leading to the processor. Inside the unit is a compressor, the same type that cools a freezer. The compressor compresses a gas (or mixture of gases) which condenses it into a liquid. Then, the liquid is pumped up to the processor, where it passes through an expansion device, this can be from a simple capillary tube to a more elaborate thermal expansion valve. The liquid evaporates (changing phase), absorbing the heat from the processor as it draws extra energy from its environment to accommodate this change. The evaporation can produce temperatures reaching around −15 to -150  degrees Celsius. The gas flows down to the compressor and the cycle begins over again. This way, the processor can be cooled to temperatures ranging from −15 to −150  degrees Celsius, depending on the load, wattage of the processor, the refrigeration system and the gas mixture used. This type of system suffers from a number of issues but mainly one must be concerned with dew point and the proper insulation of all sub-ambient surfaces that must be done (the pipes will sweat, dripping water on sensitive electronics).

Alternately a new breed of cooling system is being developed inserting a pump into the thermo siphon loop. This adds another degree of flexibility for the design engineer as the heat can now be effectively transported away from the heat source and either reclaimed or dissipated to ambient. Junction temperature can be tuned by adjusting the system pressure; higher pressure equals higher fluid saturation temperatures. This allows for smaller condensers, smaller fans and/or the effective dissipation of heat in a high ambient environment. These systems are in essence the next generation liquid cooling paradigm as they are approximately 10 times more efficient than single phase water. Since the system uses a dielectric as the heat transport media, leaks do not cause a catastrophic failure of the electric system.

This type of cooling is seen as a more extreme way to cool components, since the units are relatively expensive compared to the average desktop. They also generate a significant amount of noise, since they are essentially refrigerators, however the compressor choice and air cooling system is the main determinant of this, allowing for flexibility for noise reduction based on the parts chosen.

Liquid nitrogen

Liquid nitrogen may be used to cool an overclocked PC.

As liquid nitrogen evaporates at -196 °C, far below the freezing point of water, it is valuable as an extreme coolant for short overclocking sessions.

In a typical installation of liquid nitrogen cooling, a copper or aluminum pipe is mounted on top of the processor or graphics card. After being heavily insulated against condensation, the liquid nitrogen is poured into the pipe, resulting in temperatures well below -100C.

By welding an open pipe onto a heat sink, and insulating the pipe, it is possible to cool the processor either with liquid nitrogen, which has a temperature below −196°C, or dry ice. However, after the nitrogen evaporates, it has to be refilled. In the realm of personal computers, this method of cooling is seldom used in other contexts than overclocking trial-runs and record-setting attempts, as the CPU will usually expire within a relatively short period of time due to temperature stress caused by changes in internal temperature.

Liquid helium

Liquid helium, colder than liquid nitrogen, has also been used for cooling. Liquid helium evaporates at -269 °C, and temperatures ranging from -230 to -240 °C have been measured from the heatsink.

Soft cooling

Softcooling is the practice of utilizing software to take advantage of CPU power saving technologies to minimize energy use. This is done using halt instructions to turn off or put in standby state CPU subparts that aren’t being used or by underclocking the CPU.

Undervolting

Undervolting is the practice of running the CPU or any other component with voltages below the device specifications. An undervolted component draws less power and thus produces less heat. However, this generally will make a processor unstable as it no longer has the voltage necessary to carry out instructions error free. As such, in most cases undervolting is accompanied by an underclocking of the processor itself. Keeping the speed/voltage ratio allows a system to be undervolted while maintaining stability. This technique is generally employed by those seeking low-noise systems, as less cooling is needed because of the reduction of heat production.

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US and Russian communications satellites have collided in space in the first such reported mishap.

A satellite owned by the US company Iridium hit a defunct Russian satellite at high speed nearly 780km (485 miles) over Siberia on Tuesday, Nasa said.

The risk to the International Space Station and a shuttle launch planned for later this month is said to be low.

The impact produced a massive cloud of debris, and the magnitude of the crash is not expected to be clear for weeks.

The reportedly non-operational Russian satellite, weighing 950kg (2,094lb), had been launched in 1993, while the Iridium satellite weighed 560 kg and was launched in 1997.

When two such objects collide with such force, the ensuing debris can destroy other satellites, says the BBC’s Andy Gallacher in Florida.

But Nasa said the risk to the ISS and its three astronauts was low as the station orbits the earth some 435km below the course of the collision.

It is hoped that most of the wreckage from the collision will burn up in the earth’s atmosphere, our correspondent says.

Hundreds of pieces of wreckage are now being tracked, reports say, adding to the tens of thousands of objects that are routinely tracked through space.

Some 6,000 satellites have been sent into orbit since 1957.

Tens of thousands of objects are routinely tracked through space