What is a COM port? How do I know if I have one?
Known also as Serial ports or RS-232 ports, a COM port is an interface to connect serial devices. This is not as popular an interface in today’s technology because of the limitations in data transfer speed. However, the length of the cable can be up to 50 feet, beating out the length restriction of parallel port connections.
The port is a trapezoid shaped male connector located on the back of your computer, and various peripherals (almost exclusively external) can be connected through this interface.
~ Tiffany Garden