Soundcard Sockets
Here's the back view of a typical soundcard, showing the three
minijack sockets. (The 15-pin D-connector is the MIDI/game interface,
which can ignored for the purposes of recording analogue
audio):
Here is a detail of the three minijack sockets, showing
the identifying legends engraved on the plate:
And here are the sockets commonly found on a PC with built-in
sound on the motherboard: