Woohoo! I am one very happy person right now... I can confirm that this new graphics card upgrade is working in a MacPro1,1 - that is, the original Mac Pro with PCIe 1.0. The graphics card is PCIe 2.0 but it is most definitely downward compatible with 1.0. Apple doesn't tell you this so you upgrade to a new Mac Pro because you think you cannot upgrade the video card anymore on this older Mac Pro. After installing it I turned on my Mac Pro and she automatically recognized the card upon startup. You have to be running Mac OS X 10.5.7 or greater - I am running 10.6.1. Note: There are two power cables and I found the other power connector on the motherboard right beside the one that was leading to the X1900 XT card. Too easy. Warning: It is a tight fight if you have somewhat large hands like I do. This video card is quiet compared to my ATI Radeon X1900 XT w/512 MB RAM. You hear it spin up when booting the Mac Pro but after that it is very quiet. Here is the information from System Profiler... ATI Radeon HD 4870: Chipset Model: ATI Radeon HD 4870 Type: GPU Bus: PCIe Slot: Slot-1 PCIe Lane Width: x16 VRAM (Total): 512 MB Vendor: ATI (0x1002) Device ID: 0x9440 Revision ID: 0x0000 ROM Revision: 113-B7710C-176 EFI Driver Version: 01.00.318 My system is once again quiet - the way I like it.