The system board , also called motherboard , is the main unit inside the case. All the most important components are either mounted on it or connected to it. To place a chip on a system board it should be mounted onto a carrier. A carrier has standard-sized pin connectors that allow the chips to be inserted in the system board. An expansion card , also called an adapter, is a circuit board that provides additional capabilities for the computer.
Adapter cards have many types of large scale integrated circuit components installed on it.
For example, a video card controls the monitor. To connect a scanner to your computer, you would require a special card.