Apple PowerBook G3 - Manual (Page 45)

Connecting sound input and output devices
Your computer has a built-in microphone. In addition, you can connect a
PlainTalk microphone to the sound input port. (You can also connect a standard
line-level input microphone, although it is not suitable for speech recognition.)
For information on using the microphone to record sounds, see the “Sound”
topic area of Mac OS Help, available in the Help menu.
Your Macintosh PowerBook also has a stereo sound input port (on the left
side of the computer’s case, marked with the √ icon) for connecting external
sound input devices that provide line-level output. You cannot use the internal
microphone and an external sound input device, such as a PlainTalk
microphone, at the same time. For instructions on selecting a sound device,
see the “Sound” topic area of Mac OS Help, available in the Help menu.
Microphone
45 Connecting Additional Equipment