Sound Card Mixer
Sound cards provide the ability to record sound from various sources. In Windows XP each sound card present as a single audio device with mixer that allows recording application select any mixer input. Manufacturers of sound cards use different names for the same inputs that made it difficult for end users.
Starting from Windows Vista Microsoft has changed the topology of the sound card. Now, each input of a sound card present as a separate audio device.
Please note that inputs are active only if they are connected to an external device and external device turned on. Otherwise, input will be invisible for sound recorder software.