How do I run two independent graphics cards in Linux?

So I have a GTX 650 that I got for cheap when I first built my rig. Then as I got more money, I expanded my monitor support. (Now I run four monitors.) I found an HD7950 on craigslist for $50 that actually works well. I have my ultrawide gaming montior and a small side monitor ran from the HD7950 and my TV, for watching videos and my weppage screen ran from the GTX 650. But let me get to my actual problem.

I installed ubuntu GNOME 15.04. Then installed proprietary drivers for the HD7950, reboot, and now none of my monitors on the GTX 650 are recognized. After installing the nvidia drivers, I an unable to boot. I have purged the recently installed nvidia drivers, but am still unable to boot. So I install fglrx and am able to boot, but still without by GTX 650 (but I expected that).

  1. I am assuming I installed nvidia drivers incorrectly.
  2. Is there a special way to run two independent graphics cards, and if so how would I do that?

This is for Arch, but the principle is the same - never done it myself though.... no idea if it will work for you

https://bbs.archlinux.org/viewtopic.php?id=179549

You can't really do that. It has to be all AMD or all Nvidia. Unless you had a way to run a bi-system correctly this will not work.

However, this would work with onboard graphics. Having MESA installed with AMD next to it will work with UMA and PCIe x16 GPU's together, but it is a bi-system still. It's a wierd way to set up and very specific in how it works.

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Although this was interesting to read, it is about installing both for OpenCL. If I'm correct, if I would follow this, I could only run OpenCL programs on one of them. I am interested in running both for my desktop. This isn't a big deal, I can run all of my monitors on the HD7950. Just looks like I have a GPU for sale now.