The main circuit board of a computer is the motherboard, or main board. All other components and peripheral devices plug into the motherboard. It is a responsible for communicating between the different components and peripheral devices.
The motherboard serves as the placeholder for all the electronic components that will be plugged into the computer. It also contains the BIOS, or Basic Input/Output System.
Many devices plug into the motherboard into order to run. These devices can be the central processing unit, memory, graphics cards, hard drives or sound cards.
The form factor of the motherboard refers to its size. This is standardized so nearly all computers cases can run all motherboards. The most common form factor is the ATX.
Central Processing Unit
The Central Processing Unit, or CPU, is one of the most important aspects of a motherboard. The two main processer manufacturers are Intel and AMD. Due to physical differences in the way the CPU connects to the motherboard, a motherboard will support one or the other, not both.
The chipset is the actual component responsible for relaying information between the other components of the motherboard. The chipset cannot be upgraded without upgrading the whole motherboard.