The main circuit board of a microcomputer. The motherboard contains the connectors for attaching additional boards. Typically, the motherboard contains the CPU, BIOS, memory, mass storage interfaces, serial and parallel ports, expansion slots, and all the controllers required to control standard peripheral devices, such as the display screen, keyboard, and disk drive. Other circuit boards are called add-ons or expansion boards.


Because the motherboard contains the CPU, all other chips attached to the motherboard can access the CPU directly without going through the bus. For this reason, it is a good idea to fill up the motherboard completely before adding expansion boards. For example, to add memory to your system, you may be able to insert chips directly onto the motherboard instead of purchasing a separate memory board.


On most PCs, it is possible to replace the motherboard to upgrade to a faster microprocessor. Replacing the motherboard is somewhat more difficult and more expensive than adding an accelerator board, but it has two advantages: