Hardware components of the PC
Computer Buses
Expansion slots

In computers, an expansion slot (slot) on a motherboard is the method for adding capability to a computer in the form of connection sockets to fit an expansion card (card). These expansion slots provide the physical interface for the edge connectors of expansion cards to connect to the system bus. Expansion slots use a unique design of connector type for the different interface bus systems. Many motherboards use PCI slots with one or two ISA slots. This expansion slot feature ensures the ability to add new hardware capabilities if needed.