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When using crossfire, is it benefical to use two graphics cards or three?

SkScotchegg

SkScotchegg

SkScotchegg

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Hi there, can you explain weather or not I'll get a benefit of three cards or if I should just use two? I've never had crossfire or sli before. I've got my heart set on crossfire though because I want an ultimate gaming rig and I'm going to have 3 monitors with eyefinity.

I play all the games you'd expect, Crysis 2, BC2, SHift 2, Homefront, HL2, ACB, LFD2, SC2, Bulletstorm etc.

Also weather your answer is to get two graphics cards or three, can you please explain why, and also recommend which ATI card to get on OCUK?

Also I read on another forum that you have to have the right motherboard to support three graphics cards? does it just have to say crossfire spported on the motherboard spec?

And Do the graphics cards have to be exactly the same? So I'd have to buy 3X this = http://www.overclockers.co.uk/showproduct.php?prodid=GX-113-MS&groupid=701&catid=56&subcat=1752

Thanks in advance.
 
ok, first off, 2 is better than 1, 3 is better than 2. secondly, you do not only need to look out for the CF logo, but also how many PCI-E slots the motherboard has, how spaced out they are and @ what speeds they will run when 2 or more cards are fitted.
the next thing to look for is the case. will it comfortably house 3 cards with enough room for ventalation.
and finally, the psu. is it man enough to power 3 cards and does it have enough connectors for them.

once you have got all that sorted, then its a case of looking for the best card you can afford that supports 3 way crossfire.

why is it better, well because you have the GPUs calculating the stuff i guess, similar to having a dual core over a single core cpu, and then upping that to a quad core.

might be wrong though, so wait for someone to confirm.

EDIT : no the cards dont have to be the same, just the same series, ie all HD58** or HD68** or HD69** etc although they will only run at the speed of the slowest card.
 
The most frequent point I hear or read is that three cards are the sweet spot atm. I haven't had more than two myself (one dual gpu card).

I guess this is simply down to current drivers being able to communicate adequately with the game to provide a decent experience. The more variables (gpu's) you throw at something then the chances of a hiccup are elevated than in comparison with one.

When selecting a mobo you need to ensure that a) it supports crossfire, and b) what speeds the PCI-E slots run at. If each slot runs at x16 then or x8 then that should be ok. So it could look like something like : x16 / x16 / x8 - which iirc is ok, there isn't much performance drop afaik (hardly any in fact) when a lane drops to x8. I would say x16 is always the ideal 'want' but don't worry unnecessarily if the third slot doesn't reach x16. Quite a lot of mobos don't have three x16 pci-e lanes.

You can normally use the same cards of the same series, so something like a 6990 + 6950, or 3 x 6950's for example. (Personally, for the best bang for buck I'd get three 6950's. You can flash them to 6970 performing cards, though with that power at my fingertips I probably wouldn't bother, at least initially).
 
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2 is the sweet spot, gains from 3rd is nothing like the gain from 2 over 1, tho at eyefinity res 3rd card will be a little more useful. As you go beyond 2 cards issues like scaling, input lag and microstutter, etc. become more of a problem.
 
Rroff said:
2 is the sweet spot, gains from 3rd is nothing like the gain from 2 over 1, tho at eyefinity res 3rd card will be a little more useful. As you go beyond 2 cards issues like scaling, input lag and microstutter, etc. become more of a problem.
Click to expand...

I was playing BFBC2 with 4 GPUs smooth, with 3 GPUs smooth with, 2 GPUs stuttering & jerky & clearly not holding 60fps.

Its not all about how much more is added but about how much can be maintained & 3 GPUs is it.
 
If you're considering 2 or 3 cards in Crossfire or SLI see this review which will give you an indication of the difference between dual and triple card setups:

http://www.tomshardware.com/reviews/crossfire-sli-3-way-scaling,2865.html

You also need to consider what processor/motherboard combination you're going to be using. For 3 cards you're going to need three 8 lane PCI-E slots and most motherboards don't provide this. On Sandybridge, for example, most motherboards have two 8 lane slots and you have to spend around £300 on a motherboard with Nvidia's NF200 chip to get more.

And despite what is stated above some cards can't be used in a 3 card setup. ATI's 68xx series cards, for example, only have a single Crossfire connector so the most you can use is 2 cards.
 
Surveyor said:
If you're considering 2 or 3 cards in Crossfire or SLI see this review which will give you an indication of the difference between dual and triple card setups:

http://www.tomshardware.com/reviews/crossfire-sli-3-way-scaling,2865.html

You also need to consider what processor/motherboard combination you're going to be using. For 3 cards you're going to need three 8 lane PCI-E slots and most motherboards don't provide this. On Sandybridge, for example, most motherboards have two 8 lane slots and you have to spend around £300 on a motherboard with Nvidia's NF200 chip to get more.

And despite what is stated above some cards can't be used in a 3 card setup. ATI's 68xx series cards, for example, only have a single Crossfire connector so the most you can use is 2 cards.
Click to expand...

In those cases you pair a single with a dual to get Trifire.
 
Originally posted by Surveyor:
If you're considering 2 or 3 cards in Crossfire or SLI see this review which will give you an indication of the difference between dual and triple card setups:

http://www.tomshardware.com/reviews/...ling,2865.html

You also need to consider what processor/motherboard combination you're going to be using. For 3 cards you're going to need three 8 lane PCI-E slots and most motherboards don't provide this. On Sandybridge, for example, most motherboards have two 8 lane slots and you have to spend around £300 on a motherboard with Nvidia's NF200 chip to get more.

And despite what is stated above some cards can't be used in a 3 card setup. ATI's 68xx series cards, for example, only have a single Crossfire connector so the most you can use is 2 cards.
Click to expand...

Thats a good review, just finished reading it, it made me think though, it would be good to see a crossfire review with eyefinity using 3 monitors, do you think such a review exist?

EDIT: Also you said "ATI's 68xx series cards, for example, only have a single Crossfire connector so the most you can use is 2 cards." but I was thinking of going for 3xHD6950 with 2GB of GDDR5 like three of these http://www.overclockers.co.uk/showproduct.php?prodid=GX-113-MS&groupid=701&catid=56&subcat=1752 would they work?

Also why is it so complicated with crossfire? howcome some cards work and others dont, whats the deal? like you said 68xx series dont work, howcome?
 
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Originally posted by Final8y:
Final8y said:
In the case of 6xxx it would be a 6990+ 6970 or 6950.

TriFire is 3 GPUs.
Click to expand...

So are you saying 3xHD6950 wouldn't work together?

EDIT: Also, the guy above said my 3x25" monitors that are all 1080p would run at 5760x1080 resolution if I were to buy those three monitors from OCUK, and I was wondering what kind of fps would I get in crysis 2 with using that resolution on one gpu?
 
Final8y said:
In those cases you pair a single with a dual to get Trifire.
Click to expand...

Rubbish.

There are only a limited range of dual GPU cards.

The example I gave was ATI's 68xx series cards.

There is no such thing as a dual 68xx series card so the most you can ever use is 2.
 
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SkScotchegg said:
Originally posted by Final8y:


So are you saying 3xHD6950 wouldn't work together?

EDIT: Also, the guy above said my 3x25" monitors that are all 1080p would run at 5760x1080 resolution if I were to buy those three monitors from OCUK, and I was wondering what kind of fps would I get in crysis 2 with using that resolution on one gpu?
Click to expand...

Yes 3xHD6950 would work too.
 
SkScotchegg said:
Originally posted by Final8y:


So are you saying 3xHD6950 wouldn't work together?

EDIT: Also, the guy above said my 3x25" monitors that are all 1080p would run at 5760x1080 resolution if I were to buy those three monitors from OCUK, and I was wondering what kind of fps would I get in crysis 2 with using that resolution on one gpu?
Click to expand...

3xHD6950 would work together as long as you had a motherboard with enough PCI-E lanes.
 
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