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Simple question. SLI/ CrossFire

Last response: in Graphics & Displays
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August 23, 2006 9:15:21 PM

Can someone explain to me how SLI/Crossfire is different than just having 2 PCIe-16 slots ?
Does a motherboard need to specifically support SLI?

I don't think I'll need a 2nd video card for a while. But I might later want a physics card or use the PCIe-16 for something else.

Thanks.
August 23, 2006 10:12:18 PM

If your motherboard's chipset is not SLI certified or Crossfire certified, Nvidia/ATI will simply block SLI/Crossfire use within the driver.
August 23, 2006 10:38:32 PM

Quote:
If your motherboard's chipset is not SLI certified or Crossfire certified, Nvidia/ATI will simply block SLI/Crossfire use within the driver.

Yup, but drivers hacks/altered drivers can be found. Ask Wusy,
Related resources
August 23, 2006 10:45:58 PM

But then you're also limited to the hacked version. I believe the latest version of the hacked SLI drivers are based off 81.98; the latest WHQL verison is 91.31 which has other newer features not seen in release 80.
August 23, 2006 10:47:53 PM

True, but more hacked drivers are sure to come some day.
August 23, 2006 11:30:25 PM

Thanks for the info.
Just wished this was not so difficult.

So it seems there is no really big physical difference between normal 2 PCIe-16, SLI, and CF.
August 23, 2006 11:35:44 PM

Quote:
So it seems there is no really big physical difference between normal 2 PCIe-16, SLI, and CF.

No. Different SLI mobos have the PCI-E slots different lenghts aparts, so the length of the SLI bridge can be different. But that's a smalle issue.
August 23, 2006 11:40:19 PM

There are differences between SLI and Crossfire.

Crossfire requires one card to be the master card, and one card that is identical to the master card, acts as a slave. They are then connected by a special video cord that connect to both cards and the DVI or VGA from your monitor.

With SLI, you also need Identical cards, and by that I mean, if you have one 7900GTX then you will need a second 7900GTX, only you dont have to have the same company for the card. Also, where Nvidia has ATi beat, is how the cards are connected. Nvidia has a slot on the side of each card that serves as the interconnect to both cards. Usually the motherboard manufacturer will ship a SLI Connector which is a proprietary connector to connect two SLI ready cards.

I have read recently that ATi plans to have the same feature and do away with the current crossfire setup. It remains to be seen, but it would fair much better.

Also, if you buy a motherboard and are looking for SLI, then usually you will see these chipsets or names on the motherboard,
Nforce 4 SLI
for example my motherboard: Biostar NF4SLI-A9

Newer Nforce 5xx series motherboards carrying the SLI acronymn.

Crossfire will generally be the ATi chipset of Express 3200.
a b U Graphics card
August 24, 2006 1:24:49 AM

Quote:
There are differences between SLI and Crossfire.

Crossfire requires one card to be the master card, and one card that is identical to the master card, acts as a slave.


No it doesn't have to be an identical card but they do have to be from the same generation (X1600 with X1600, and X1900 with X1900 [you can do X1900GT+X1900Xfire), and the master slave issue is the same behind the scenes as SLi if you're talking about assigning VPUs render priority. However Xfire/Master cards are only required for some models, primarily the high end, so it's not a function of Xfire itself but the limitations of the hardware at the time of inception.

Quote:
They are then connected by a special video cord that connect to both cards and the DVI or VGA from your monitor.


X1300, x1600, X1800GTO don't need dongles, neither with the X1900GT, X1650 series, and X1950Pro.

Quote:
I have read recently that ATi plans to have the same feature and do away with the current crossfire setup.


I'd like to see that reading, because I don't belive it exists. Both nV and ATi are moving away from 'connected' cards moving to PCIe bus connection.

Quote:
It remains to be seen, but it would fair much better.


PCIe bus is slower for both, and nV's SLi Bridge is no better than ATi's dongle for actual function, it's more a question of asthetics. The only advantage to the SLI bridge is for Quad monitor setups, you have to decide if anyone thinks that important enough to consider.
August 24, 2006 8:28:30 PM

Well APE you definitly pointed out a lot more than I had known. I am glad you cleared that up because the impression's I had about the crossfire configurations. I now know a little more but was just trying to help, and I knew if I was wrong someone could correct me. 8)

I will correct the statement about ATi planning to move away from the dongle, I want to restate that and say, some people think they should move away from it... :wink:
August 24, 2006 9:37:00 PM

Most examples of Xfire use an external compositing chip to combine the images, similar to the proprietary Alienware system that composited on a PCI card in the R9700 days.

This does have some disadvantages and limitations, if you are running an x800 or x850 xfire setup, you are stuck with 1600x1200@60Hz, which can be limiting for a system designed for high resolutions (i'd go blind at 60hz :/  )

The x1000 series have moved that limit much further into the distance however :) 

The compositing chip is also the reason for the 'master' cards - only these contain them.

IMHO, Xfire feels like it was rushed out to compete with SLi, and doesnt feel as 'polished'. One cannot argue with results however, and the fact that the x1900XTX is the better card atm, means that two of them in Xfire is still better than two 7900GTXs in SLi :) 

I wish nVidia would wake up and smell the coffee and enable SLi on the 975x though....
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