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Motherboard

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Motherboard
The ASUS CUSL2-C motherboard
Connects toMicroprocessors via:

Main memory via:

  • Slots

Peripherals via one of:

Expansion cards via one of:

Form factorsATX
microATX
Others
Common manufacturersIntel
Abit
MSI
ASUS
Foxconn
Gumstix
Others

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.[1]

The basic purpose of the motherboard 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

File:ASRock K7VT4A Pro Mainboard Labeled English.png
The modern ASRock K7VT4A Pro motherboard by Asus. The chipset on this board consists of northbridge and southbridge chips.

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:

The Octek Jaguar V motherboard from 1993[1]. This board has 5 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. 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

File:Motherboard diagram.png
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:

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.

History

File:In9-32x-max top 500.jpg
A modern motherboard by Universal Abit (IN9 32X SLI)[2]. Note the heatsinks for cooling of motherboard components, and the large number of peripheral connectors and components.

Prior to the advent of the Apple II in 1977, a computer was usually built in a case or mainframe with components connected by a backplane consisting of set of slots themselves connected with wires. The CPU, memory and I/O peripherals were housed on individual PCBs or cards which plugged into the backplane.

With the arrival of the microprocessor, it became more cost-effective to place the backplane connectors, processor and glue logic onto a single "mother" board, with video, memory and I/O functions on "child" cards — hence the terms "motherboard" and daughterboard. The Apple II computer featured a motherboard with 8 expansion slots.

During the late 1980 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 early 2000s, many 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.

Form factors

Motherboards are produced in a variety of 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, 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.

These are some of the more popular motherboard form factors:

  • PC/XT - created by IBM for the IBM PC, its first home computer. As the specifications were open, a large number of clone motherboards were produced and it became a de facto standard.
  • AT form factor (Advanced Technology) - created by IBM for its PC/XT successor, the AT. Also known as Full AT, it was popular during the era of the Intel 80386 microprocessor. Superseded by ATX.
  • Baby AT - IBM's 1985 successor to the AT motherboard. Functionally equivalent to the AT, it became popular due to its significantly smaller size.
  • ATX - created by Intel in 1995. As of 2007, it is the most popular form factor for commodity motherboards.
  • ETX - used in embedded systems and single board computers.
  • microATX - a smaller variant of the ATX form factor (about 25% shorter). It is compatible with most ATX cases, but supports fewer expansion slots due to its smaller size. Very popular for desktop and small form factor computers as of 2007.
  • FlexATX - a subset of microATX developed by Intel in 1999. Allows more flexible motherboard design, component positioning and shape.
  • LPX - based on a design by Western Digital, it allowed smaller cases than the AT standard, by putting the expansion card slots on a riser (image). LPX was never standardized and generally only used by large OEMs.
  • NLX - a low-profile design released in 1997. It also incorporated a riser for expansion cards, and never became popular.
  • BTX (Balanced Technology Extended) - a standard proposed by Intel as a successor to ATX in the early 2000s.
  • Mini-ITX - a small, highly-integrated form factor created by VIA in 2001. Mini-ITX was designed for small devices such as thin clients and set-top boxes.
  • WTX - created by Intel in 1998. A large design for servers and high-end workstations featuring multiple CPUs and hard drives.

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.

Visual Comparison

This image compares the sizes of common form factors to ISO 216 paper sizes (e.g. A4):

See also

Motherboards for sale at retail.

Notes

  1. ^ The abbreviated name "mobo" is generally credited to the magazine Maximum PC.
  2. ^ In the case of CPUs in BGA packages, such as the VIA C3, the CPU is directly soldered to the motherboard.
  3. ^ More power-hungry components such as disk drives and modern graphics cards are often connected to the power supply via separate, dedicated connectors
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