Mac Pro: Conflict between ATI Radeon X1900 XT and GeForce 7300 GT when simultaneously installed

We previously reported on a snippet in Apple's Mac Pro developer note, which states:

"Note: The Mac Pro does not simultaneously support an ATI graphics card and an NVIDIA graphics card."

We've now received reports from readers who have actually installed both ATI and  graphics cards simultaneously in a Mac Pro, with (expectedly) poor results. Specifically, it appears that when both an ATI and NVIDIA card are installed in a Mac Pro, Core Image elements/applications will not function properly on displays driven by the ATI card, but will operate on displays driven by the NVIDIA card.

Core Image components will operate properly with the ATI card when no NVIDIA card is also installed.

"I've run across a fairly significant conflict in the Mac Pro regarding Core Image and the combination of an ATI Radeon X1900 XT and NVIDIA GeForce 7300 GT when running in the same machine. My I ordered my new Mac Pro with the X1900, and added the 7300 as a separate item to install myself. These 2 cards drive 4 monitors (1 DVI flat panel, and 3 standard VGA CRTs). I first noticed trouble when the 'RSS Visualizer' screen saver would not function. Even the preview would not work, causing the System Preferences to instantly quit, often without an error message.

"Assuming a System problem associated with my setup, I installed a completely clean OS on a separate drive, with the same results. I then played around with the Visualizer in SaverLab, and discovered it would open on either of the two screens attached to the NVIDIA card, but not on the screens attached ATI card. I tried other applications, and discovered that no application which uses Core Image will run on ATI card in this configuration Some apps, such as 'Image Tricks' will run until you make use of a filter or effect which uses Core Image technology. Other apps, like 'iMaginator' will fail instantly. Most of the time the OS doesn't even provide an error message, the program just bails instantly.

"The workaround is either to remove the NVIDIA card, at which point Core Image works properly on the ATI card, or to use the NVIDIA card to drive the primary screen (i.e. the one with the menu bar), and then remember not to move the windows of any Core Image application to a screen driven by the ATI card. Obviously this isn't an ideal situation as you will normally want your best monitor to run on your primary (fastest) video card."

Last week we also noted an issue where, when two graphics cards are installed in a configuration where one card is running at 16 lane speed, and the other at 8 lane speed (the maximum throughput possible in a two card configuration) issues such as an inability to display graphic content in some applications, and a lack of screen refresh manifest.

Feedback? Late-breakers@macfixit.com.

For further coverage, see our Mac Pro special report.

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