1. Sometimes called the system board or main board, the motherboard is the main circuit board of a PC. The motherboard typically contains the processor (or CPU), BIOS (basic input/output system), memory, mass storage interfaces, serial and parallel ports, expansion slots, and all the controllers required to communicate with standard peripheral devices, such as the display screen, mouse, keyboard and disk drive. Collectively, some of the chips which reside on the motherboard are known as the motherboard\'s chipset.