Any card (PCI/PXI/AT/PCMCIA) that serves as an interface between a PC and the rest of the world can be considered to be an "interface card". However, in the specific case of serial interface cards, their function is to expand the number of serial (RS-232 or RS-422/485) communication ports on a PC. Serial communication is used widely in automation and control since the physical layer is inexpensive, and the technology is well established. Examples of devices that serial interfaces can communicate with include bar code readers, LCD displays, and a wide range of lab equipment.
