A motherboard is the central printed circuit board (PCB) in many modern computers and holds many of the crucial components of the system, while providing connectors for other peripherals. The motherboard is sometimes alternatively known as the main board, system board, or, on Apple computers, the logic board.It is also sometimes casually shortened to mobo (Dell XPS M1210 Battery) .
Prior to the advent of the microprocessor, a computer was usually built in a card-cage case or mainframe with components connected by a backplaneconsisting 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 (Dell Studio XPS 1340 Battery) .
During the late 1980s and 1990s, it became economical to move an increasing number of peripheral functions onto the motherboard (see below). 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 (Dell Studio XPS 1640 Battery) .
As of 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 gaming and computer graphics typically retained only the graphics card as a separate component (Dell Vostro 1710 Battery) .
The early pioneers of motherboard manufacturing were Michronics, Mylex, AMI, DTK, 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 (ASUS EEE PC900 battery) .
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 (Dell RM791 battery) .
In modern terms this would includeembedded 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.
A motherboard, like a backplane, provides the electrical connections by which the other components of the system communicate, but unlike a backplane, it also connects the central processing unit and hosts other subsystems and devices (Sony VGP-BPS13 battery) .
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, although in modern computers it is increasingly common to integrate some of these peripherals into the motherboard itself (Sony VGP-BPL9 battery) .
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 (Sony VGP-BPL11 battery) .
Modern motherboards include, at a minimum:
- sockets (or slots) in which one or more microprocessors may be installed
- slots into which the system's main memory is to be 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 (Sony VGP-BPL15 battery)
- 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, which receive electrical power from the computer power supply and distribute it to the CPU, chipset, main memory, and expansion cards (Dell Inspiron E1505 battery) .
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 (Dell Latitude E6400 battery) .
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 (HP Pavilion dv6000 Battery) .
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.
Main article: CPU socket
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) (Sony Vaio VGN-FZ31S battery) .
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 (Sony Vaio VGN-FZ31S battery) .
CPU sockets 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 on the motherboard. A CPU socket type and motherboard chipset must support the CPU series and speed.
Block diagram of a modern motherboard, which supports many on-board peripheral functions as well as several expansion slots (Hp pavilion dv6000 battery) .
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 (Sony VGN-FW11S Battery) .
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 (Sony VGP-BPS13A/B Battery) :
- 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 (Sony VGP-BPS13B/B Battery)
- 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 such highly integrated motherboards are available for as little as $30 in the USA (Toshiba Satellite P10 Battery) .
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 PCI) (SONY VAIO VGN-FZ210CE Battery) .
A standard EATX motherboard will have one PCI-E 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 SLI(for Nvidia) and Crossfire (for ATI) (SONY VAIO VGN-FZ38M Battery) .
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, 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's case (SONY VAIO VGN-FZ31z Battery) .
Ethernet is also included. 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 output without the need for any extra components. This allows computers to be far more multimedia-based than before. Some motherboards have their graphics chip built into the motherboard rather than needing a separate card. A separate card may still be used (SONY VAIO VGN-FZ31E Battery) .
Temperature and reliability
Main article: Computer cooling
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, it can cause the 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 fansmounted on their heat sinks, due to rising clock speeds and power consumption (SONY VAIO VGN-FZ31J Battery) .
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 (SONY VAIO VGN-FZ31M Battery) .
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 (SONY VAIO VGN-FZ31B Battery) .
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 peripheralhardware but to aging capacitors on PC motherboards. Ultimately this was shown to be the result of a faulty electrolyte formulation (SONY VGP-BPS13 Battery) .
For more information on premature capacitor failure on PC motherboards, see capacitor plague.
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 (Dell Precision M70 Battery) .
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 (Acer Aspire One battery) .
Main article: Comparison of computer form factors
microATX form factor motherboard
Motherboards are produced in a variety of sizes and shapes called computer form factor, some of which are specific to individual computer manufacturers (Toshiba Satellite L305 Battery) .
However, the motherboards used in IBM-compatible commodity computers have been standardized to fit various case sizes. As of 2007, 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. The current desktop PC form factor of choice is ATX (Toshiba Satellite M65 battery) .
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 (Toshiba Satellite T4900 Battery) .
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
Main article: booting
Motherboards contain some non-volatile memory to initialize the system and load an operating system from some external peripheral device (Toshiba PA3399U-2BRS battery) .
Microcomputers such as the Apple II and IBM PC usedROM 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) (Dell Latitude E6400 battery) .
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 (Toshiba Satellite A200 Battery) .
(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 (Toshiba Satellite 1200 Battery)
- CD-ROM drive
- DVD-ROM drive
- SCSI hard drive
- IDE, EIDE, or SATA hard disk
- External USB memory storage device (Toshiba NB100 Battery)
Any of the above devices can be stored with machine code instructions to load an operating system or program.
A chipset, PC chipset or chip set refers to a group of integrated circuits, or chips, that are designed to work together. They are usually marketed as a single product (Toshiba Satellite M300 Battery) .
Diagram of a motherboard chipset
In computing, the term chipset is commonly used to refer to a set of specialized chips on a computer's motherboard or an expansion card. Inpersonal computers the first chipset for the IBM PC AT was the NEAT chipset by Chips and Technologies for the Intel 80286 CPU (Dell INSPIRON 1525 battery) .
Chipsets are the main controllers on the motherboard - they allow the CPU to interface with the various components and expansion cards installed .”
Based on Intel Pentium-class microprocessors, the term chipset often refers to a specific pair of chips on the motherboard: the northbridge and thesouthbridge (Dell Inspiron Mini 10 Battery) .
The northbridge links the CPU to very high-speed devices, especially main memory and graphics controllers, and the southbridge connects to lower-speed peripheral buses (such as PCI or ISA). In many modern chipsets, the southbridge actually contains some on-chip integrated peripherals, such as Ethernet, USB, and audio devices (Dell Latitude D830 Battery) .
A chipset is usually designed to work with a specific family of microprocessors. Because it controls communications between the processor and external devices, the chipset plays a crucial role in determining system performance.
The manufacturer of a chipset often is independent from the manufacturer of the motherboard. Current manufacturers of chipsets for PC-compatiblemotherboards include NVIDIA, AMD, VIA Technologies, SiS, Intel and Broadcom (Dell Studio 1735 Battery) .
Apple computers and Unix workstations from Sun, NeXT, SGI, and others have traditionally used custom-designed chipsets; now that Sun and Apple both have x86 processors in at least some of their lines of products, they have begun to use standard PC chipsets in some of their computers. Some server manufacturers also develop custom chipsets for their products (Dell Latitude D620 Battery) .
In the 1980s, Chips and Technologies, founded by Gordon Campbell, pioneered the manufacturing of chipsets for PC-compatible computers. Computer systems produced since then often share commonly used chipsets, even across widely disparate computing specialties. For example, theNCR 53C9x, a low-cost chipset implementing a SCSI interface to storage devices, could be found in Unix machines such as the MIPS Magnum, embedded devices, and personal computers (SONY VAIO VGN-FZ150E Battery) .
In home computers, game consoles and arcade game hardware of the 1980s and 1990s, the term chipset was used for the custom audio and graphics chips. Examples include the Commodore Amiga's Original Chip Set or SEGA's System 16 chipset (Dell Studio 1555 Battery , Dell Latitude D610 Battery).