Dual nVIDIA GeForce 8800 GT GPUs

Well,

It seems to me that this 8800 GT GPU looks like it was made to be combined with another 8800 GT GPU (because it's so thin that it fits in a single slot and it has an SLI cable connector on it).

Apple offers a version of this 8800 GT that is compatible with the 2008 Mac Pro with its 1.6 MHz bus and PCI Express 2.0 slots.

The Apple Store also sells another version of the 8800 GT that is backward compatible with my 2007 Mac Pro with its 1.33 MHz bus and earlier version of PCI Express slots (not PCI Express 2.0).

There are reports that using two of these 8800 GT GPUs in slots 1 and 2 (I know, I know... the $) and connected by an SLI ribbon cable (not the bridge) will provide one of the best GPU solutions available for the Mac Pro (make it longer lasting) and also enable nVIDIA's SLI technology to work in Boot Camp and native in Leopard (10.5.2 or better).

My question is: Does anyone know of or have personal experience with a dual 8800 GT GPU SLI linked configuration like this in either the 1st or 2nd generation Mac Pros?

I'd be most grateful for any input on this...

TIA and Cheers,

tyvol

Message was edited by: tyvol

Mac Pro, 2 x 3 GHz Quad-Core Intel Xeon, Mac OS X (10.5.3), GPU=X1900 512MB, HD's 1 Raptor (150GB), 3 Seagate (750 GB), Canon LiDE Scanner

Posted on Jun 12, 2008 3:06 PM

21 replies

tyvol Author

Level 1

65 points

Jun 20, 2008 11:23 PM in response to rob_ART

rob_ART,

Fascinating!

If a 3870 X2 can work on an early Mac Pro, I'd be most grateful to hear about it!

Triple Crossfire or quadruple Crossfire (2 times the 3870 x2) should be as good as it gets...

Many thanks for sharing your knowledge/experience rob_ART!

Let us know, if you have time, how your work on the 3870 x2 is progressing...

Kindest regards,

tyvol

Jun 21, 2008 2:17 PM in response to tyvol

SLI DOES NOT WORK ON THE MAC PROS!

SLI requires an NVIDIA southbridge on the motherboard, not for technical reasons, but simply so they can sell motherboards. If you have two 8800 GTs in your system, even with the ribbon cable, they are not running in SLI. They are simply two graphics cards that you can add extra displays to.

To use SLI, you need either a motherboard with an nForce chipset, or the Intel Skulltrail motherboard, which has an NVIDIA southbridge for that very purpose.

In order for Crossfire to compete, ATI allows it on any motherboard. If you have multiple Radeon cards that meet Crossfire requirements, they will be able to run in Crossfire mode under Windows, but there simply aren't drivers for this under Mac OS.

The HD 3870 isn't much better or worse than the 8800 GT. Some games, they come real close, but others, the 8800 GT does much better. I think it will be cheaper, and I think the Radeons are better at Core Graphics, but for games, the 8800 GT is a better bet.

Jun 21, 2008 10:47 PM in response to ZeelessOneLive

You guys make the ATI 3870s sound better and better...

So, SLIing two 8800s in a mac Pro doesnt do anything extra? Sorry if I misunderstand you, but are you saying that you only get the performance of one card with two 8800s, and not 175+%?

What exactly is this crossfire, how will the performance of two ATI 3870s (crossfire) compare to that of two GeForce 8800s (SLI) for gaming (Crysis)?

Thanks.

Jun 22, 2008 6:05 AM in response to tyvol

This page shows the 3870 X2 vs the 8800 GT vs the 3870, as well as some other cards.

http://www.anandtech.com/video/showdoc.aspx?i=3209&p=5

Two 3870s should be a little more powerful than one 3870 X2, if that helps.

Also, SLI bridges come with motherboards, so you'd have to find one special if SLI did work at all. Crossfire bridges come with the cards, so you'd be set there.

Jul 30, 2008 2:20 PM in response to ZeelessOneLive

I would love to know how to enable CrossFire with two 3870's. I have them installed with the bridge connector in my early 2008 Mac Pro, and I have the latest ATI drivers. However, I can't find any CrossFire settings in the ATI control panel. 😟

Jul 30, 2008 6:41 PM in response to tyvol

One thing you might want to know is that the first 8800 GT must be in slot 1 to get the 16x factor. The second 8800 GT needs to be in slot 4 to get the 8x factor. Slots 2 and 3 don't allow maximum performance (at 1x or 4x).

High power cards should be used only in slots 1 and 2
<http://developer.apple.com/documentation/Hardware/Conceptual/HWtech PCI/Articles/pciimplementation.html#>
"When populating the four PCI Express slots, you need to conform to the following total wattage rules:

Slots one and two (not including aux power), max slot power per slot: 75 W
Slots three and four (not including aux power), max slot power per slot: 40 W
All four slots (not including aux power), max total power: 200 W
Max aux power per connector: 75 W
Max aux power for both connectors: 150 W
Max total PCI Express power (slot power and aux connector power): 300 W
Note: To ensure optimal cooling in the PCI Express rack, high power cards using aux power are not recommended in slots three and four."

For the early Mac Pro, you can set slots 1 and 2 to x8, which is still a lot of bandwidth.

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Dual nVIDIA GeForce 8800 GT GPUs