Why do we need audio out put (SPDIF)?

Hi,

In our PC we already have an inbuilt sound Card, for audio output.

1- Why do we need a separate audio output (SPDIF) in graphics cards

2- How much is the voltage in SPDIF cable?

3- Can I run the graphics card, without connecting the SPDIF cable, taking the video output from graphics card and audio output from the inbuilt sound card?

Thanks for your valuable time in advance!!

SPDIF is for sending audio to a tv using a HDMI cable, if you have normal speakers you can use your sound card, if you only have a tv with inbuilt speakers you might want to send the audio over a HDMI cable and for that you need to use the graphics card to do so.

info obn voltages and such - http://en.wikipedia.org/wiki/Spdif

this isnt cuda relate, please post it in the appropriate section of the forum.