Does Target Display Mode use Extra CPU Power?

[keithlittle]

Hi Friends,

I have 2017 MacBook Air. I'm using a 2010 iMac 27" in Target Display Mode as an extra monitor.

I can't find this answer anywhere else online but I'm wondering if running the extra monitor in Target Display Mode uses extra CPU power from the MacBook.

I'm sometimes struggling to get enough power out of the MacBook (I know I shouldn't expect too much) and wondering if I'm over-taxing it by asking it to run an external display or if it makes no real difference.

I don't know, for example, if Target Display Mode uses the iMac's GPU or the MacBooks.

Any information would greatly help! Thanks, all.

 

[gammamonk]

My work MacBook Pro is a 13" 2017 with the base i5, it should be pretty comparable. I drive a 4K tv and keep the laptop in clamshell mode. I can't say it uses any more CPU really. Your iMac is acting as a monitor and is less than 4K so that shouldn't be too demanding. If your CPU is an i3 or i5 it's just not going to be that great. I can't even play 4K60 video on this thing, it just doesn't have the horsepower.

I'm holding out for the bigger M1 laptops to come out and I'll ask work to pony up.

 

[Toutou]

In Target Display Mode the iMac is just a monitor, the MacBook does all the drawing. Drawing the UI on a second monitor does eat up some resources (both the CPU and GPU -- just check the WindowServer process in ActivityMonitor), but generally the performance hit of drawing the UI is negligible even on huge screens unless you're moving windows around (in which case there's much more redrawing going on and both the CPU and GPU usage spike).