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 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
- 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.
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.