Motherboard

A motherboard is the central or primary circuit board making up a complex electronic system, such as a modern computer. It is also known as a mainboard, baseboard, system board, or, on Apple computers, a logic board, and is sometimes abbreviated as mobo.

Most after-market motherboards produced today are designed for so-called IBM-compatible computers, which hold over 96% of the personal computer market today. Motherboards for IBM-compatible computers are specifically covered in the PC motherboard article.

The basic purpose of the motherboard, like a backplane, is to provide the electrical and logical connections by which the other components of the system communicate.

A typical desktop computer is built with the 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 are typically attached to the motherboard via edge connectors and cables, although in modern computers it is increasingly common to integrate these "peripherals" into the motherboard.

Components and functions
The motherboard of a typical desktop consists of a large PCB. It holds electronic components and interconnects, as well as physical connectors (sockets, slots, and headers) into which other computer components may be inserted or attached.

Most motherboards include, at a minimum:

* sockets (or slots) in which one or more microprocessors (CPUs) are installed[4]
* 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 and circuits, which receive electrical power from the computer power supply and distribute it to the CPU, chipset, main memory, and expansion cards.[5]
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. 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.

Integrated peripherals
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,[7] 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 such highly-integrated motherboards are available for as little as $30 in the USA.