Hello, I think I may have uncovered something very interesting with the MacPro1,1 (and possibly most other MacPro's since they all use EFI). Recently I wanted to give a go at Bitcoin/Litecoin mining however my video card (nVidia Quadro 4500 FX) is not working correctly due to CUDA not being fully supported in higher revs of OS X (and probably the fact that my 4500 FX Quadro is a PC card that was flashed with an EFI32). This being the case for months I gave up on most GPU based mining (tried LTC mining using the 3.0 Ghz Xeon CPU's but only getting about 5 Kh/s hashing power even with Xeon's that have big L1/L2 cache). I remembered that I had a moderate PC video 3D card sitting on the spare pile - nVidia geForce 8800 GT. This card did NOT have an Apple EFI/firmware on it. I confirmed this by removing my Quadro and trying the 8800 and upon turning on the Mac I get black screen (but still do hear the "chime") to indicate system is booting up, but video card is not passing EFI check. So yesterday I had an idea. What if I was to boot up my MacPro1,1 using my Mac/EFI32-compatible video card (the Quadro), but put the PC/non-EFI video card (8800) in one of the other PCI-E slots (yet kept my monitor DVI cables going to my Quadro vid card). Sure enough the MacPro1,1 booted up into OS X (10.7 Lion). I went into Applications > Utilities > System Information and under the Graphics/Displays category both of the video cards were listed! OSX loaded the drivers to support the 8800 GT even though it did not have an Apple EFI. Seems you need only 1 vid card with an EFI in the MacPro to get it to boot: NVIDIA Quadro FX 4500: Chipset Model: NVIDIA Quadro FX 4500 Type: GPU Bus: PCIe Slot: Slot-1 PCIe Lane Width: x16 VRAM (Total): 512 MB Vendor: NVIDIA (0x10de) Device ID: 0x009d Revision ID: 0x00a1 ROM Revision: 3452 NVIDIA GeForce 8800 GT: Chipset Model: NVIDIA GeForce 8800 GT Type: GPU Bus: PCIe Slot: Slot-3 PCIe Lane Width: x4 VRAM (Total): 512 MB Vendor: NVIDIA (0x10de) Device ID: 0x0611 Revision ID: 0x00a2 ROM Revision: preset 1.0.0 Since this 8800 GT seems to be functioning I opened up the BitMinter client (for Bitcoin mining) and sure enough it sees the GeForce 8800 GT and is mining 17-18 Mh/s with it! Had this spare 8800 sitting in a box for longest time, and was going to try to flash it with the proper 32 bit EFI but it seems as long as I run my monitor off an EFI video card and then fill the PCI-X slots with non-EFI vid cards may be able to do some serious mining with the MacPro1,1. So - moral of the story is - anyone who wants to use an older MacPro for BTC/LTC mining - keep your primary EFI video card as primary and then try adding other (non-EFI) video cards to the remaining PCI-E slots. Adjust your 4x/8x/16x lanes accordingly using the "Expansion Slot Utility" and you may be able to do some unexpected GPU intensive applications (without a monitor hooked to those vid cards).