SLI working on Mac Pro

ampd

macrumors regular
Jan 10, 2006
114
0
This is great news! Hopefully we will be getting the drivers to do this in OSX...
 

cw2k

macrumors newbie
Feb 22, 2006
24
0
ezekielrage_99 said:
Does the SLI just only work with Windows or does Mac OSX supports this as well?
Just Windows, when you boot back into OSX the cards function as 2 separate cards as they would normally do.

The driver works with 7900/7600/7300 cards (does not work with 7950GX2).

Newer drivers have not been modified yet as NVidia has put in integrity checks to prevent this type of mod working.

Source of the driver: http://www.xtremesystems.org/forums/showthread.php?t=106212

I will do further tests later today.
 

Spanky Deluxe

macrumors 601
Mar 17, 2005
4,856
387
London, UK
This is outstanding news!! 2x7300gt cards is a quite reasonable mid range solution performance and cost wise.

An SLI connector isn't required by the latest of nVidia drivers anyway - I found that out by losing my connector in my PC for months. I thought I'd left it at home when I went for Uni. When I was packing up my stuff to come back I found it behind the computer. Doh!

Not having an SLI connector is more of a bottleneck on high end cards but on low end cards it doesn't make much of a difference.

Edit: CW2K, welcome to MacRumors btw! Are you a poster over at xtreme? I used to be but got burnt by destroying two processors with a phase change system so have left the xtreme tweaking to the pros now. Could you run any benchmarks? Lost coast for example? High res?

Edit 2: Also do those drivers support coolbits and can you try overclocking the cards a bit? They appear to be quite well designed 7300s so they could maybe be overclocked a bit. Overclocking 7300s seem to give a great boost in performance: http://www.techspot.com/review/6-geforce_7300gt_sli_performance/
 

Mr. Mister

macrumors 6502
Feb 15, 2006
440
0
Very interesting but it's a shame there isn't slotspeed configuration where there are two 16x's and the rest are something really low, the highest you can get two slots to go right now is 8x.
 

ksz

macrumors 68000
Oct 28, 2003
1,669
60
San Jose, CA
Mr. Mister said:
Very interesting but it's a shame there isn't slotspeed configuration where there are two 16x's and the rest are something really low, the highest you can get two slots to go right now is 8x.
In SLI configuration, I believe nVidia's cards only use 8 lanes each.
 

godbout

macrumors regular
Jun 22, 2005
182
0
Montreal, Canada
MovieCutter said:
Kick ass. I wonder if this would work with two PC GPUs? Dual x1950's here I come!!!
I don't know about that because I am not sure that crossfire has chipset independent drivers

Dual 7950GTX here I come!!! ;)
 

godbout

macrumors regular
Jun 22, 2005
182
0
Montreal, Canada
aiongiant said:
i wonder if a quad sli system will work :D
I don't think that there are enough PCI-e lanes for quad SLi on the macpro chipset... well not 4X8 anyways...

your options are:

Slot 1 Slot 2 Slot 3 Slot 4
Option 1 8-lanes 8-lanes 1-lane 8-lanes
Option 2 8-lanes 8-lanes 4-lanes 4-lanes
Option 3 16-lanes 1-lane 1-lane 8-lanes


(I think)
 

ksz

macrumors 68000
Oct 28, 2003
1,669
60
San Jose, CA
godbout said:
No if you have a Nvidia chipset that supports SLi then you can have 2 16x lanes that will be used for the two graphics cards.
It's a little more complicated than that. AnandTech has an explanation of SLI here. The second paragraph states:

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.
The takeaway message I believe is:

  1. All PCIe graphics cards require x16 *physical* slots. This is simply the specification for any graphics card.
  2. Not all PCIe slots are *electrically* x16. This is limited by the chipset. Most chipsets do not allow two 16-lane electric configuration.
  3. The MacPro has 5 PCIe slots. They are all physically x16 slots, but not electrically. If all 5 slots were electrically x16, the total lanes would have been too many for the chipset to handle.
  4. Because Apple wants to allow multiple graphics cards in order to support multiple monitors, and because all PCIe graphics cards require x16 *physical slots*, all 5 of the MacPro's slots are physically x16.
  5. However, only 1 slot can be set electrically to x16.
  6. This is not limited to Apple's motherboard. Most PC motherboards are also limited to one *electrical* x16 slot.
  7. If you put two graphics cards in the MacPro, one of them will use at most eight electric lanes. The real-world impact of this is negligible as indicated by AnandTech. The difference between 16 electric lanes and 8 isn't anything to worry about.
  8. Finally, nVidia supports the following electric lane configurations for SLI:
  • x8 and x8 (officially)
  • x16 and x2 (unofficially)
 

CyberPrey

macrumors regular
Aug 10, 2006
209
0
IGH, MN
#8, That is incorrect. Check both Asus and nvidia's websites.

Nvidia fully supports a 16x/16x SLI configuration on the NForce 4 SLI Chipset.

I haven't read the spec's fully in a while, but in order to use a 16x/16x SLi setup, both the northbridge AND southbridge dedicate lanes to each card... 16x physically AND electrically...
 

ksz

macrumors 68000
Oct 28, 2003
1,669
60
San Jose, CA
^^^ You're right about the A8N32-SLI motherboard and the nForce4. AnandTech's article is dated November 2004 at which time x16/x16 was not supported. What is interesting, though, is that the MacPro supports x8/x8, which has only a "negligible" hit on performance.
 

CyberPrey

macrumors regular
Aug 10, 2006
209
0
IGH, MN
I'm only right about 1 or 2 times a year :)

While I 'think' i will be happy for quite some time using 1 16x card in the Mac Pro, I have a feeling that there will probably be some sort of change in the Apple computer line that DOES allow for 2 16x graphics cards to be used.
 

ksz

macrumors 68000
Oct 28, 2003
1,669
60
San Jose, CA
CyberPrey said:
I'm only right about 1 or 2 times a year :)
One third of the year is still left; looks like you may be improving your batting average!

I wasn't expecting SLI to work at all, so the fact that it actually does and that it is supported by these el cheapo 7300GTs is something to get excited about. Do two 7300GTs equal one X1900XT? Or at least come close?
 

topgunn

macrumors 65816
Nov 5, 2004
1,460
1,272
Houston
ksz said:
One third of the year is still left; looks like you may be improving your batting average!

I wasn't expecting SLI to work at all, so the fact that it actually does and that it is supported by these el cheapo 7300GTs is something to get excited about. Do two 7300GTs equal one X1900XT? Or at least come close?
Thats a reasonable question. What does a X1900 or even a 7900GT or GTX (non-SLI) score in 3D Mark '06?
 

DougTheImpaler

macrumors 6502a
Feb 28, 2006
558
49
Central Illinois
ksz said:
Do two 7300GTs equal one X1900XT? Or at least come close?
No, but you get two things instead:

1.) Save $200 over an X1900XT
2.) Shorter shipping delay than the X1900XT

All told, they're probably about as fast as a single 7600GT or 7600GS, which is still a better gaming option than the X1600's in the iMac
 

topgunn

macrumors 65816
Nov 5, 2004
1,460
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