On one computer I owned, it was entirely in the audio driver -- so when I switched to Linux, I was surprised to see that the headphones and speaker had independ

On one computer I owned, it was entirely in the audio driver -- so when I switched to Linux, I was surprised to see that the headphones and speaker had independently controls for volume levels. (The latter was labelled "Mono Out", and the behaviour where plugging in headphones cut off speakers didn't happen on that Linux install.)