How many pins does standard serial port have?

A common serial port has either nine pins (by far the most common) or sometimes on very old equipment 25 pins. It turns out that they are completely compatible with a very simple adapter... the older standard just used a wider connector.

The nine pins are arranged in two offset rows. The port (on a computer) is "male" in that the metal pins are sticking out, with a metal shield around it forming a trapezoid with slightly rounded corners.