A port is a channel through which a device communicates with the operating system. From a hardware perspective, a port is a “receptacle” into which a terminal or modem cable might be physically connected.
However, a port is not strictly a physical receptacle, but an entity with hardware (pins and connectors) and software (a device driver) components. A single physical receptacle often provides multiple ports, allowing connection of two or more devices.
Common types of ports include serial, parallel, small computer systems interface (SCSI), and Ethernet.
Devices that have been designed according to RS-232-C or RS-423 standards, this include most modems, alphanumeric terminals, plotters, and some printers. These devices can be connected interchangeably, using standard cables, into serial ports of computers that have been similarly designed.
When many serial port devices must be connected to a single computer, you might need to add an adapter board to the system. The adapter board, with its driver software, provides additional serial ports for connecting more devices than could otherwise be accommodated.