Choose System Preferences > Energy Saver. Uncheck Automatic Graphics Switching and the more powerful card will always be enabled. If you check it, it will choose the lower powered GPU when the more powerful one is not needed. More info: http://support.apple.com/kb/ht4110
Hmmmm, but what happens in the case of a new Mac Pro where the cards are identical, but one happens to be driving all the monitors? Does PPcc know to choose the one that's not doing any other work for accelerating effects during playback?
Under normal circumstances, PP will use the card driving the Primary Display for hardware acceleration.
OK, so then, in the new Mac Pro, the second video card sits idle, since it doesn't actually drive any of the displays?
And in the case of a Windows machine with two video cards, each with it's own monitor hooked up to it, if I have one set as my primary display, it will use that card for playback acceleration, even if it's the other monitor that's hooked up to a different video card, that I'm doing playback on?
Are the card identical, same driver?
I know 7.2.1. on Windows can now make use of both cards under certain conditions. Not sure about Macs, but I'd assume the same.
[Moved to Hardware forum.]
I thought both cards were used for rendering, but playback was only 1 card.
But for the scenario I'm talking, it would be two different models of card under windows. But even if they were identical, I'm still unclear on what happens. I'd rather not buy the second card only to find out it's useless to me for playback purposes.
Adobe uses the Video card driving the Primary display in Windows by default. If you go into the Nvidia control panel you can set the preference for the GPU you want to use by default. Then Adobe will follow that. If a card is not selected there and does not drive the primary monitor then it sits idle during realtime playback with Premiere.
Hmmmm. Is there something equivalent for the new Mac Pro? We've got 3 monitors hooked up, including a 4k display, so it sounds like the other card is just sitting idle at all times when using premiere. Anyway to force the other card into use?
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The OS determines most of it. As far as I know it is based on which PCI slot they are in, sorted by closest to the CPU to furthest, and independent of monitors being attached because the ordering is fixed at system startup while monitors can come and go. This can of course lead to some bad cases when the primary GPU doesn't have a monitor attached but those are edge cases. The one case of reordering we do over the OS list is we always put discrete devices ahead of integrated devices.
Premiere will only use 1 GPU for playback and all others can be used for export.
Hope this information is helpful.
The primary Display adapter is determined first by the bios/firmware which can be selected on PC and then changed if configured differently in the OS by the Primary monitor. All testing I have done Adobe follows the OS listed primary display if you cant change the GPU acceleration setting in the Nvidia control panel. I am not aware of a simialr setting in OSX.