Upgrading the Mac Pro: Adding a 2nd GPU
tl;dr- Yes, you can add a 2nd GPU; OS X will ignore it; Windows will use it. Make sure to disable the card in the 1st slot to use it for gaming. Apple makes great hardware, there’s no doubt about it. However, occasionally they make decisions that not only boggle the mind but are completely infuriating. Like putting non-standard ports on a laptop and charging twenty bucks for the proper adapter cable! A similar problem I ran into recently is the issue of the graphics card in the Mac Pro: only specially branded “Mac-compatible” GPUs will work in OS X. What’s the problem with that you ask? Availability and pricing.