Does a 2nd monitor slow down a mac?

[Tex-Twil]

Hi,
I have the Retina, 15-inch, Mid 2015 MBP and I have one 2K and one 1K monitor plugged both via miniDP

https://everymac.com/systems/apple/...-iris-only-mid-2015-retina-display-specs.html


I have the feeling that the entire macOS UI is slightly slow even during normal usage and I'm trying to find out why. Is it possible that it is because I have two monitors? I think this model has only the integrated graphic card.

cheers,
Tex

 

[keysofanxiety]

Yes that's correct, running external monitors will hammer the graphics much more than running from the internal display only. This will be amplified with integrated graphics as it wouldn't be as powerful compared to discreet graphics.

As such UI features may seem slightly slower, though CPU/RAM intensive tasks shouldn't noticeably suffer.

 

[Tex-Twil]

My GPU usage is almost idle though:
\

I'll try to disconnect the 1K to see if there is a difference. This feeling might also be due to the lag of the magic mouse

 

[ZapNZs]

Yes. You will also notice that the idle temperatures are higher when running one display, and even higher when running two. For example, with the built in display only, my idle is around 100-105F (mid-2014 15-inch 2.5 dGPU model). With one 1080p display + the built in display, my idle is around 120-125F. With a second 1080p display added, it's around 150F. Alternatively, with a single 4k display, the idle temp is around 40+F degrees higher. During CPU-intensive tasks, the fans are noticeably louder, and IMO there is a slight slowdown of productivity tasks (my assumption has always been that the higher idle temperatures results in quicker thermal throttling.) During CPU + GPU intensive tasks, this is much more pronounced (and Intel Power Gadget's frequency graph looks like a Richter Scale during an earthquake of moderate intensity.)