I have a 2,1 Mac Pro 8 core 3 Ghz ATI X1900XT. This is a long winded tale which showed me that I COULD use my ATI X1900XT to upgrade to Mavericks on my Mac Pro. I also have a 2014 Mac Mimi Core i5 OS X 10.10.1 I wanted to upgrade the Mac Pro to Mavericks with a PC MSI r5770 1 gig. ========================================== I've seen in many different forums that my original ATI X1900XT 512mb cannot be used but I thought that I would give it a try anyway. 1. I prepared a Mavericks 9.1 boot USB as per the many guides available on the net. 2. I installed OS X 10.6.8 on a spare SATA drive in an external enclosure connected to the Mac Mini. 3. Booted up the Mac Mini with the Mavericks USB card connected and selected it (USB card ) to boot from. ========================================== INSTALLATION of Mavericks from the USB boot drive 4. Started installing from the USB card to the external 10.6.8 drive. 5. After the install finished I restarted the Mac Mini with the new external-Mavericks drive still connected. 6. Started MainMenu Pro ( Terminal can be used also ) to show all invisible files. 6.1 This allowed me to do the Tiamo efiboot replacement process on the external drive. ============================= 7. Disconnected the external newly Mavericks installed HD and installed it the Mac Pro ( with my old ATI X1900XT installed too. ( NOTE : The new Mavericks drive was the ONLY drive in the Mac Pro) 8. Booted . . . .. . YES ! my ATI X1900XT booted Mavericks and ran well on 1920 X 1080 ! So much for the doom sayers. ========================================== 9. Graphics card upgrade : MSI r5770 Hawk 1 gig I found this 2nd. hand PC card for about US$ 49 here in Japan where I live. It booted up OOTB in 10.6.8 - no boot screens of course. This card has not been flashed and won't be in the foreseeable future as I rarely need the Apple boot screens unless I come across another MSI r5770 Hawk to be used as a guinea pig. In any case Clover allows boot selection. 9.1 Shut down the Mac Pro, removed the X1900XT and replaced it with the MSI r5770 Hawk connected using a DVI-VGA adapter to a Samsung SMS23A350H LED monitor (The Mac Mini is connected to the HDMI Samsung port.) Booted . . .yes ! Happiness ! Mavericks + MSI r5770 Hawk. There ares probably still quite a few Mac Pro 1,1 & 2,1 owners with ATI X1900XTs installed. I posted to show that you CAN install Mavericks using this still handy card that was great in it's day. More to the point, there are still plenty of cheap MSI r5770 Hawk cards available on NewEgg & Amazon, this card is a huge upgrade from the X1900XT eg : I could not even run X-Plane Version 10 ( flight simulator ) on the X1900XT on 10.6.8 With the non-flashed MSI r5770 Hawk installed it runs very well in almost full on graphics settings. The r5770 Hawk has two silent fans, used only one 6 pin PCI power connector cable and is . .faaast. Cheers.