A motherboard (sometimes alternatively known as the mainboard, system board, planar board or logic board^[1], or colloquially, a mobo) is a printed circuit board (PCB) found in all modern computers which holds many of the crucial components of the system, such as thecentral processing unit (CPU) and memory, and provides connectors for other peripherals.

Motherboard specifically refers to a PCB with expansion capability - the board is the "mother" of all components attached to it, which often include sound cards, video cards,network cards, extra hard drives or other forms of persistent storage, TV tuner cards, cards providing extra USB or Firewire slots, and a variety of thousands of other kinds of custom components. (The term mainboard is applied to devices with a single board and no additional expansions or capability - in modern terms this would include controlling boards in televisions, washing machines and other embedded systems, which are not true motherboards.A motherboard provides the electrical connections by which the other components of the system communicate. 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, 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.