2+ Nvidia 7300GT

[nsknike]

I was just wondering if you get 2 or more of these cards, is it setup in an SLI configuration when you boot into windows? Is there any gain using two or more, other than being able to use 2 or more 30 inch monitors?

 

[ksz]

The Mac Pro has only one x16 PCIe slot, hence no SLI. You also need nVidia's chipset to get SLI support. Since I believe Intel played a large role in the design of the Mac Pro motherboard, I doubt they used nVidia parts anywhere.

 

[dmw007]

The Mac Pro has only one x16 PCIe slot, hence no SLI. You also need nVidia's chipset to get SLI support. Since I believe Intel played a large role in the design of the Mac Pro motherboard, I doubt they used nVidia parts anywhere.

I believe that ksz is correct- no SLI in the Mac Pros.

 

[Eidorian]

I thought that in SLI mode both slots clocked down to x8. I don't think that the Mac Pro has the required NVidia chipsets either. It isn't in the developer notes. Still, hope that you can run a GX2 card in OS X/Windows. We're running on EFI and not open firmware. I don't see why retail PC video cards won't work on the Mac Pro outside of software drivers.

 

[ksz]

I thought that in SLI mode both slots clocked down to x8.

"Clocking down" is not technically correct as it is the number of lanes that are reduced, not the clock speed. An excerpt from Anandtech explains this further, but it's a bit cryptic:

"NVIDIA’s first task in assuring that the load distributed to both GPUs would be balanced and symmetrical was to equip their nForce4 SLI chipset with identical width PCI Express graphics slots. By default, PCI Express graphics cards use a x16 slot, which features 16 PCI Express lanes offering 8GB/s of total bandwidth. Instead of outfitting their chipsets with 16 more PCI Express lanes, NVIDIA simply allows the number of lanes to be reconfigurable to either a single x16 slot or two x8 slots, with the use of a little card on the motherboard itself. The physical slots themselves are both x16 slots, but electrically they can be configured to be two x8 slots. This won’t cause any compatibility issues with x16 cards, as they will just use fewer lanes for data transfers, and the real world performance impact is negligible in games, which is what NVIDIA is counting on."

I think what this means is that PCIe graphics cards use 16 lanes by default, but when SLI is enabled, the SLI Chipset only uses 8 lanes per card. The real world impact of this is negligible, but the graphics cards themselves must still plug into full-size 16-lane (x16) slots.

 

[Eidorian]

"Clocking down" is not technically correct as it is the number of lanes that are reduced, not the clock speed. An excerpt from Anandtech explains this further, but it's a bit cryptic:

"NVIDIA’s first task in assuring that the load distributed to both GPUs would be balanced and symmetrical was to equip their nForce4 SLI chipset with identical width PCI Express graphics slots. By default, PCI Express graphics cards use a x16 slot, which features 16 PCI Express lanes offering 8GB/s of total bandwidth. Instead of outfitting their chipsets with 16 more PCI Express lanes, NVIDIA simply allows the number of lanes to be reconfigurable to either a single x16 slot or two x8 slots, with the use of a little card on the motherboard itself. The physical slots themselves are both x16 slots, but electrically they can be configured to be two x8 slots. This won’t cause any compatibility issues with x16 cards, as they will just use fewer lanes for data transfers, and the real world performance impact is negligible in games, which is what NVIDIA is counting on."

I think what this means is that PCIe graphics cards use 16 lanes by default, but when SLI is enabled, the SLI Chipset only uses 8 lanes per card. The real world impact of this is negligible, but the graphics cards themselves must still plug into full-size 16-lane (x16) slots.

Thanks for the explanation.

 

[nsknike]

Thanks for the quick replies.

 

[dmw007]

Thanks for the explanation.

Yes, thanks for the clarification on this matter ksz.