In a modern PC the serial port is generally no longer used. At one point this was an extremely useful port in the computer, allowing the connection of a mouse, modem, printer and many other types of serial device.
The serial ports colour is green and has a male D shape.
Serial cables can only go in one correct way and have to be lined up correctly. The pins in the port are more robust than that of a keyboard cable, however, they could be damaged if the cable is forced in the wrong way.
Click on this wiki resource to review serial ports.
Next: Other Connections