The first two generations of Apple’s Mac Pro, the MacPro1,1 and MacPro2,1, do not officially run OS X later than 10.7.5. However, there is a modified EFI bootloader available which emulates the EFI64 interface on EFI32 machines. The original version available at Google Code supports OS X 10.9, and there’s a newer one available at Github which also does OS X 10.10. You simply drop in a new boot.efi in two places and add your board ID to the list of supported systems.
The resulting system works perfectly fine, which makes me wonder why Apple didn’t come up with a solution like this themselves. In any case, it extends the life of 2006 and 2007 Mac Pros beyond last year’s end-of-support for OS X Lion.
Since OS X 10.7 and higher included graphics drivers that not only supported the official Apple-supplied GPUs with EFI-compatible firmwares, but pretty much any off-the-shelf Nvidia or AMD GPU, GPUs have become quite easy to upgrade in Mac Pros (the classic tower cheese grater Mac Pro, not the new black trash can Mac Pro). The only thing you lose is the boot screen, so you still need to keep around that original GPU to debug the machine if it doesn’t boot.
These upgraded GPUs work fine with the modified bootloader as well, however if you try to install multiple GPUs (e.g. if you want to drive more than two displays or develop CUDA code and would like to run it in the debugger), only one of them will actually output video.
The solution to make multiple GPUs work in Macs running OS X versions they don’t officially support is surprisingly simple:
sudo /usr/libexec/PlistBuddy -c "Add :IOKitPersonalities:AppleGraphicsDevicePolicy:ConfigMap:Mac-F4208DA9 string none" /System/Library/Extensions/AppleGraphicsControl.kext/Contents/PlugIns/AppleGraphicsDevicePolicy.kext/Contents/Info.plist sudo /usr/libexec/PlistBuddy -c "Add :IOKitPersonalities:AppleGraphicsDevicePolicy:ConfigMap:Mac-F4208DC8 string none" /System/Library/Extensions/AppleGraphicsControl.kext/Contents/PlugIns/AppleGraphicsDevicePolicy.kext/Contents/Info.plist sudo touch /System/Library/Extensions
So here we are, running a 2006 MacPro1,1 with two EVGA Nvidia GT610 1GB cards, driving three Apple Cinema Displays.