From ECDL.web

A motherboard, also known as a mainboard, system board, or logic boards on Apple computers, and sometimes abbreviated as mobo (generally credited to the magazine Maximum PC) is the central or primary circuit board making up a complex electronic system, such as a modern computer.

A typical computer is built with the microprocessor, main memory, and other basic components on the motherboard. Other components of the computer such as external storage, control circuits for video display and sound, and peripheral devices are typically attached to the motherboard via ribbon cables, other cables, and power connectors.

[edit] Form factors

Motherboards are available in a variety of form factors, which usually correspond to a variety of case sizes. The following is a summary of some of the more popular PC motherboard sizes available:

• IBM PC XT - (8.5 × 11" or 216 × 279 mm) the original open motherboard standard created by IBM for the first home computer, the IBM-PC. It created a large number of clone motherboards due to its open standard and therefore became the de facto standard.
• AT form factor (Advanced Technology) - (12 × 11"–13" or 305 × 279–330 mm) the first form factor to gain wide acceptance, successor to PC/XT. Also known as Full AT, it was popular during the 386 era. Now obsolete, it is superseded by ATX.
• Baby AT - (8.5" × 10"–13" or 216 mm × 254-330 mm) IBM's successor to the AT motherboard, it was functionally equivalent to the AT but gained popularity due to its significantly smaller physical size. It usually comes without AGP port.
• ATX - (12" × 9.6" or 305 mm × 244 mm) the evolution of the Baby AT form factor, it is now the most popular form factor available today.
• ETX Form Factor - (12" × 13" or 305mm × 330 mm) used in embedded systems and single board computers.
• Mini-ATX - (11.2" × 8.2" or 284 mm × 208 mm) essentially the same as the ATX layout, but again, with a smaller footprint.
• microATX - (9.6" × 9.6" or 244 mm × 244 mm) again, a miniaturization of the ATX layout. It is commonly used in the larger cube-style cases such as the Antec ARIA.
• FlexATX - (9.6" × 9.6" or 244 × 244 mm max.) a subset of microATX allowing more flexible motherboard design, component positioning and shape.
• LPX - (9" × 11"–13" or 229 mm × 279–330 mm) based on a design by Western Digital, it allows for smaller cases based on the ATX motherboard by arranging the expansion cards in a riser (an expansion card in itself, attaching to the side of the motherboard. This design allows the cards to rest parallel to the motherboard as opposed to perpendicular to it. The LPX motherboard is generally only used by large OEM manufacturers.
• Mini LPX - (8"–9" × 10"–11" or 203–229 mm × 254–279 mm) a smaller subset of the LPX specification.
• NLX - (8"–9" × 10"-13.6" or 203–229 mm × 254–345 mm) a low-profile motherboard, again incorporating a riser, designed in order to keep up with market trends. NLX never gained much popularity.
• BTX (Balanced Technology Extended) - (12.8" × 10.5" or 325 mm × 267 mm max.) a newer standard proposed by Intel as an eventual successor to ATX.
• microBTX (10.4" × 10.5" or 264 mm × 267 mm max.) and picoBTX (Intel 2004; 8.0" × 10.5" or 203 mm × 267 mm max.) - smaller subsets of the BTX standard.
• Mini-ITX - (6.7" × 6.7" or 170 mm × 170 mm max; 100W max.) VIA's highly integrated small form factor motherboard, designed for uses including thin clients and set-top boxes.
• WTX (Workstation Technology Extended) - (14" × 16.75" or 355.6 mm × 425.4 mm) a large motherboard (more so than ATX) designed for use with high-power workstations (usually featuring multiple processors or hard drives.

While most desktop computers use one of these motherboard form factors, laptop (notebook) computers generally use highly integrated, customized and miniaturized motherboards designed by the manufacturers. This is one of the reasons that notebook computers are difficult to upgrade and expensive to repair - often the failure of one integrated component requires the replacement of the entire motherboard, which is also more expensive than a regular motherboard due to the large number of integrated components in it.

[edit] CPU sockets

Main article: CPU socket

The term CPU socket (or CPU slot) is widely used to describe the connector linking the motherboard to the CPU(s) in certain types of desktop and server computers. There are different slots and sockets for CPUs, and it is necessary for a motherboard to have the appropriate slot or socket for the CPU. Newer sockets, those with a three digit number, are named after the number of pins they contain. Older ones are simply named in the order of their invention, usually with a single digit.

[edit] Sockets supporting Intel processors

• Socket 6 - 80486DX4
• Socket 7 - Intel Pentium and Pentium MMX, AMD K6 and some Cyrix CPUs)
• Socket 8 - Intel Pentium Pro
• Slot 1 - Intel Pentium II, older Pentium III, and Celeron processors (233 MHz - 1.13 GHz)
• Slot 2 - Intel Xeon processors based on Pentium II/III cores
• Socket 370 - Celeron processors and newer Pentium IIIs (700 MHz - 1.4 GHz)
• Socket 423 - Intel Pentium 4 and Celeron processors (based on the Willamette core)
• Socket 478 - Intel Pentium 4 and Celeron processors (based on Northwood, Prescott, and Willamette cores)
• Socket 479 - Intel Pentium M and Celeron M processors (based on the Banias and Dothan cores)
• Socket M - Intel Core processors (based on the Yonah core)
• Socket 603 / 604 - Intel Xeon processors based on the Northwood and Willamette Pentium 4 cores
• Socket T / LGA 775 (Land Grid Array) - Intel Pentium 4, Core 2, and Celeron processors (based on Northwood, Prescott, Conroe, Kentsfield, and Cedar Mill cores)
• LGA 771 (Land Grid Array) - Intel Xeon Core 2, and based on Woodcrest cores

[edit] Sockets supporting AMD CPUs

• Slot A - original AMD Athlon processors
• Socket 462 (aka Socket A) - newer AMD Athlon, Athlon XP, Sempron, and Duron processors
• Socket 754 - lower end AMD Athlon 64 and Sempron processors with single-channel memory support
• Socket 939 - AMD Athlon 64, AMD Athlon 64 FX, AMD Athlon 64 X2, and AMD Opteron processors with dual-channel memory support
• Socket 940 - AMD Opteron and early AMD Athlon FX processors
• Socket AM2 - Sempron, AMD Athlon 64, AMD Athlon 64 X2, AMD Athlon 64 FX and AMD Opteron
• Socket F - AMD Opteron and high-end AMD Athlon 64 FX

[edit] Peripheral card slots

There are usually a number of expansion card slots to allow peripheral devices and cards to be inserted. Each slot is compatible with one or more industry bus standards. Commonly available buses include: PCI (Peripheral Component Interconnect), PCI-X, AGP (Accelerated Graphics Port), and PCI Express.

ISA was the original bus for connecting cards to a PC. Despite significant performance limitations, it was not superseded by the more advanced but incompatible MCA (Micro Channel Architecture) (IBM's proprietary solution which appeared in their PS/2 series of computers and a handful of other models) or the equally advanced and backward-compatible EISA (Extended Industry Standard Architecture) bus. It endured as a standard feature in PCs till the end of the 20th century, aided first by the brief dominance of the VESA (Video Electronic Standards Association) extension during the reign of the 486 and later by the need to accommodate the large number of existing ISA peripheral cards. The more recent PCI bus is the current industry standard, which initially was a high-speed supplement to ISA for high-bandwidth peripherals (notably graphics cards, network cards, and SCSI host adaptors), and gradually replaced ISA as a general-purpose bus. An AGP slot is a high speed, single-purpose port designed solely for connecting high performance graphics cards (which produce video output) to the monitor. Both AGP and PCI buses are marked for replacement by PCI Express, although this is unlikely to happen prior to 2006 because of the large established base of AGP/PCI motherboards and add-in cards.

A typical motherboard of 1999 might have had one AGP slot, four PCI slots, and one (or two) ISA slots; since about 2002 the last ISA slots in new boards have been replaced with extra PCI slots. Sometimes an Advanced Communications Riser slot is used instead on less expensive motherboards.

As of 2001, most PCs also support Universal Serial Bus (USB) connections, and the controller and ports required for this are usually integrated onto the motherboard. An ethernet interface and a basic audio processor are now almost universally integrated into current motherboards as well.

[edit] Temperature and reliability

Generally, motherboards are air cooled with heat sinks on the larger chips such as the northbridge and CPU, and they have monitored sockets for case fans. Newer motherboards have integrated temperature sensors to detect motherboard and CPU temperatures, which can be used by the BIOS or Operating system to regulate fan speed. The removal of waste thermal energy became a major concern for workstation PCs around 2000, with the problem becoming more severe over time as computer systems continued to consume more and more power.