What does the HDMI do to my GPU?

[Cappuccino]

I can connect an HDMI cable from my HDMI to the monitor, but what does it do and do I need to do it? I have the r9 390. Also, when I do plug both in my screen goes black and I only see my mouse. Why does that happen? So obviously I have to unplug the HDMI and go from there

 

[RussianSensation]

I can connect an HDMI cable from my HDMI to the monitor, but what does it do and do I need to do it? I have the r9 390. Also, when I do plug both in my screen goes black and I only see my mouse. Why does that happen? So obviously I have to unplug the HDMI and go from there

When connecting a videocard to the monitor, you would use just 1 cable.

If your monitor has DVI input, you just use the DVI-to-DVI cable.

If your monitor has HDMI input, you can use HDMI-to-HDMI cable. For simplicity, this cable is just called HDMI cable.

You would not use HDMI + DVI cables together. You pick one or the other.

 

[Cappuccino]

When connecting a videocard to the monitor, you would use just 1 cable.

If your monitor has DVI input, you just use the DVI-to-DVI cable.

If your monitor has HDMI input, you can use HDMI-to-HDMI cable. For simplicity, this cable is just called HDMI cable.

You would not use HDMI + DVI cables together. You pick one or the other.

Oh I see.
BUT why is there one for my GPU?

 

[Deders]

It's so you have the option to use either.

Or you could connect 2 monitors to 1 graphics card.

Or you could use the DVI cable for your graphics and the HDMI cable to send audio to a receiver/hi-fi.

 

[LTC8K6]

Are you possibly referring to the motherboard video connectors versus the graphics card video connectors?