A motherboard is the central printed circuit board (PCB) in some complex
electronic systems, such as modern personal computers. The motherboard is
sometimes alternatively known as the mainboard, system board, or, on Apple
computers, the logic board. It is also sometimes casually shortened to mobo.
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 backplane.
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.
Popular personal 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 archaically 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 with the capability to
add/extend its performance/capabilities with the addition of "daughterboards".
Overview
Most computer motherboards produced today are designed for IBM-compatible
computers, which currently account for around 90% of global PC sales. A
motherboard, like a backplane, provides the electrical connections by which the
other components of the system communicate, but unlike a backplane, it also
hosts the central processing unit, and other subsystems and devices.
Motherboards are also used in many other electronics devices such as mobile
phones, stop-watches, clocks, and other small electronic devices. A typical
desktop computer has its 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 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 are installed
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 flickers, which receive electrical power from the
computer power supply and distribute it to the CPU, chipset, main memory,
and expansion cards.
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.
CPU sockets
A CPU socket or CPU 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 providing
a physical structure to support the CPU, providing 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.
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, 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.
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