Motherboard

History

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 a 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.

Intro to the 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.^[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

The 2004 K7VT4A Pro motherboard by ASRock. 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:

• Socket
• The CPU and working storage (the RAM modules)
  
• Expansion cards, also called adapters (PCI, AGP and AMR slots, etc.)
• 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
• Plugs, connectors and port
• The motherboard also contains a number of inputs and outputs, to which various equipment can be connected. Most ports (also called I/O ports) can be seen where they end in a connector at the back of the PC.
• power connectors which receive electrical power from the computer power supply and distribute it to other components

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

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 4 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 6-channel audio and S/PDIF output
• fast Ethernet network controller for 10/100 Mbit networking
• USB 2.0 controller supporting up to 8 USB ports
• IrDA controller for infrared communications (e.g. with a handheld remote control)
• 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.

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, many 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.