What is the difference between the external microphone and the internal microphone of Panasonic mdh 1 camera?

What's the difference between an external microphone and a built-in microphone of a camera? Exactly, unlike being used alone, an external microphone can easily pick up weak sound, and it can be placed where the built-in microphone can't. ......

The internal input points of the external microphone and the internal microphone of the camera are preamplifiers. ...