An expansion card (also expansion board, adapter card or accessory card) in computing is a printed circuit board that can be inserted into an expansion slot of a computer motherboard to add additional functionality to a computer system. Connectors mounted on the bracket allow the connection of external devices to the card. Depending on the form factor of the motherboard and case, around one to seven expansion cards can be added to a computer system.
The group of expansion cards that are used for external connectivity, such as a network, SAN or modem card, is commonly referred to as input/output cards (or I/O cards).
