dGPU needed for external monitors?

[MovieGuy34]

Hello all

I have the new 15 inch 2.3 dGPU rMBP. I use it at work and I connect it to a 21inch Gateway monitor via HDMI. According to graphic card status it says it's turned on the dGPU. Is it really necessary to have this running? Shouldn't the Iris Pro be powerful enough to power a monitor?

Thanks!

 

[dukebound85]

my 13in mbp that only has an igu can run external monitors just fine

 

[MovieGuy34]

Yeah my 2008 macbook used to run it no problem. I'm just surprised to see this new one automatically switching to it. Was just wondering if anyone knew of any reasons why it might need to be on. It's not really a big deal. I keep the computer plugged in pretty much all day.

 

[c1phr]

This has been an "issue" with all of the automatic graphics switching models. They always call the dedicated card whenever an external monitor is plugged in, even if the extra power isn't really necessary. I guess Apple just assumes that if you're plugged into a monitor, you can plug the machine into a power outlet.

http://apple.stackexchange.com/questions/27337/is-a-macbook-pro-not-able-to-use-dual-screen-on-the-integrated-graphics-card
https://discussions.apple.com/thread/5006479

 

[dusk007]

The problem is Apple ONLY wired the dGPU to the external video ports. The internal screen is wired to a mux chip that switches the input. That mux chip is connected to both GPUs.
The alternative would be a very complex logicboard with lots more muxing hardware for all the ports. Or Apple could switch to the IMO vastly superior software based graphics switching (like Optimus from Nvidia or Enduro from AMD). In the latter only the integrated GPU is directly connected to the output ports and the dedicated GPU only supplies processing power when needed but lets the integrated handle the display output.

Apple does neither so you have to use the dGPU even if all you do is show still images like slides on a projector for some presentation while you talk.