The motherboard is the main printed circuit board (PCB) that is connected to the most crucial components in a computer. It also provides many connectors to attach peripheral (external) components. The motherboard is also known as mainboard or system board.
In today's computer systems the most common design for motherboards is the ATX design, a follow up of the AT board, based on the IBM AT motherboard. A variation of the ATX design is the microATX for very compact computers. Most of the basic components that come with a current system board are:
- A CPU socket - to insert a CPU into. CPU stands for Central Processing Unit.
- One or two large chips - the Southbridge and optionally the Northbridge. Usually these chips are covered by a heatsink.
- System memory slots - to insert RAM-modules into.
- Expansion slots (PCI, PCI-express, 'riser cards') for expansion cards for dedication functions such as video, audio, networking etc..
- Various ports and connectors for input and output signals. These can be serial ports (RS232), parallel ports, PS/2 mouse/keyboard ports, infrared interface, floppy disk controller, USB, SATA, ATA, Firewire, connectors for hard disks, DVD, CD-drives, etc.
- Some smaller electrical components such as the voltage regulator module (VRM), a small battery (to store clock settings and motherboard configuration), jumpers, a reprogrammable flash memory that holds the software for the BIOS (Basic Input Output System).
- Power connector ports for the motherboard itself, the CPU, and several fans.
Many functions that were only available as separate expansion cards in the past, are now integrated on the motherboard, such as an integrated graphics processor (IGP), integrated audio, telephony and networking facilities. These functions are performed by the Southbridge chip. The integration of such functionalities has diminished the necessity for dedicated expansion cards.
For mobile computer motherboards the peripheral slots are limited to typically 2 externally accessible slots, while the rest is integrated on the motherboard. Graphics chips are embedded on the motherboard, as are the audio, network and modem chips. The PCCard slot has become obsolete, and is being replaced by ExpressCard.
Courtesy of the French Energy Agency ADEME, Future Electronics project. Expanded by VHK.