Serial Port
Introduction
A Serial Port is a generic term for a port on a computer that can be connected to other devices. This may be a proprietary connector with a few wires in it; an AppleBus/AppleTalk connector to connect a printer, modem or another computer; or (by far the most common usage) an RS-232 port with a 9-pin D-connector (DE-9) for asynchronous communications (see Communications). All have one thing in common: the data is sent over a small number of wires (usually one in each direction) in serial fashion, rather than all at once in parallel.
But since "Serial Port" is usually used to refer to the COM Port that is found on the PC (to distinguish it from the rarely-seen-nowadays "Parallel Port"), this page will concentrate on that. Refer to the specific pages for other port types. This page will cover the physical port itself, its signals, and how these signals are commonly used.