In
personal computers, a
motherboard is the central
printed circuit board (PCB) in many modern
computers and holds many of the crucial components of the system, providing connectors for other peripherals. The motherboard is sometimes alternatively known as the
mainboard,
system board, or, on
Apple computers, the
logic board.
[1] It is also sometimes casually shortened to
mobo.
Motherboard for an Acer desktop personal computer, showing the typical components and interfaces that are found on a motherboard. This model was made by Foxconn in 2008, and follows the
ATX layout (known as the "
form factor") usually employed for desktop computers. It is designed to work with AMD's
Athlon 64 processor.
A motherboard of a Vaio E series laptop (right)
[edit] History
Prior to the advent of the
microprocessor, a computer was usually built in a card-cage case or
mainframe with components connected by a
backplane consisting 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 backplate. 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. 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.
The early pioneers of motherboard manufacturing were
Micronics,
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. 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 applied to devices with a single board and no additional expansions or capability. In modern terms this would include
embedded systems and controlling boards in televisions, washing machines, etc. A motherboard specifically refers to a printed circuit board with expansion capability.
[edit] Overview
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.
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.
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.
Modern motherboards include, at a minimum:
- sockets (or slots) in which one or more microprocessors may be installed[2]
- 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
- 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.[3]
The Octek Jaguar V motherboard from 1993.
[4] This board has few onboard peripherals, as evidenced by the 6 slots provided for
ISA cards and the lack of other built-in external interface 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. 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.
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.
[edit] CPU sockets
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). 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. 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.
[edit] Integrated peripherals
Block 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,
[5] 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
[update] such highly integrated motherboards are available for as little as $30 in the US.
[edit] 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). 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). 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.
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 contain video outputs on the back panel for integrated graphics solutions (either embedded in the motherboard, or combined with the microprocessor, such as the Intel HD Graphics). A separate card may still be used.
[edit] Temperature and reliability
Motherboards are generally
air cooled with
heat sinks often mounted on larger chips, such as the
Northbridge, in modern motherboards. Insufficient or improper cooling can cause damage to the internal components of the computer and cause it 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 fans mounted on their
heat sinks, due to rising clock speeds and power consumption. 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.
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.
A 2003 study
[6] 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 peripheral
hardware but to aging
capacitors on PC motherboards. Ultimately this was shown to be the result of a faulty electrolyte formulation.
[7]
A microATX motherboard with some faulty capacitors.
- 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. While most capacitors are rated for 2000 hours of operation at 105 °C,
[8] 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,
[9] which significantly reduce life expectancy. Inadequate case cooling and elevated temperatures easily exacerbate this problem. It is possible, but tedious and time
