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What are the real world advantages of SLI/XFire?

Ninja Please!

Ninja Please!

Ninja Please!

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Hey mates,

I have read up on sli and crossfire and there I had some questions reguarding what I read.

Some claim that it doesn't work or doesn't work very well with some games and therefore you would be better off to have just one good card

I have also heard that 2 cards with 512mem is not the same as one card with 1gb mem. Also that if I went SLI with my 285 I was told I would not be able to up the draw distance more or anything because It wouldn't use the vid ram on the second card like I would think it would.

So is SLI just basically for more fps? I know it helps with larger resolutions so is it useless unless you have dual monitors or high resolutions?

Thanks for any help in advance.
 
its worth it if you want max resolution on a 22 or 24" lcd. But if you want to do it mainly just for gta iv you will be disappointed, i think sli + xfire are broke in this game.
 
Two 285s in SLi should rip through anything, even Crysis. That said, check online benchmarks to see how SLi scales in your favourite games; performance can vary from absolutely no increase in performance to almost twice the performance, depending also on the game setting, resolution and filter (AA and AF).

You are right though, the 2x1gb of ram is not shared between the GPUs, but instead each GPU has it's own gb of memory, which are identical copies of each other.
 
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HA!

I knocked up a 6600GT SLI setup purely because I wanted to play with SLI as cheap as possible.

Its kind of gone ridiculous now cos I have 4 SLI setups in my house

6600GT
7600GT
7800GT
260GTX

The thing is, that for the price they have cost me, I should have just not bothered and bought a single card.

I was told a short while back, that the only time SLI is going to be any good, is when you buy 2 of the fastest cards on the planet. Then, and only then will SLI be faster.

Anotherweek down the line, they will bring out another card, and thus renders your 2 SLI cards almost useless because only one of the newest card is probably the same speed as your SLI setup.

Now, of course, this is untrue but its not THAT far off... Not really.

SLI setups look good however.

And when I was running the 6600GT and comparing it to the SLI 6600GT setup, it did make a difference, it really did.

I was able to run Medal Of Honour : Airborne that much better, UT3, hell even Doom3 was useable as opposed to the one, but in truth, the gam,es that were jerky with one card was still jerky in SLI, just slightly less.
 
The real world advantages are simply improved performance, however at a cost. Higher power consumption, case temps for a start. Also games react differently to cf/sli set-ups so you will be failr dependant on drivers as to what gains you might see.

Btw you are using an oc 920 and gtx 285, is performance really not acceptable? what res do u play at?
 
More often than not if you intend to Xfire/SLI it's best to do it with the two fastest cards out, as obviously by the time you've purchased two cheaper cards you may have either spent more money, or barely surpassed the performance of a more expensive single card whilst using more power, creating more heat and decreased compatability.

There are of course exceptions to this rule. Though only ever dependant on market value. 4850 Xfire when it was released was a killer setup, and 8800GT SLI when the prices got dirt cheap was also pretty tough to beat for the price. GTX260 SLI before the price of the GTX280 plummeted was also a good blend of price/performance/power. Other factors like most skt775 Nforce mobos (Needed to run SLI) being rubbish were a consideration also.

Essentially though they're a power users setup, and IMO should only be considered when the most powerful single GPU card doesn't give you enough grunt.
 
Adrianr said:
Essentially though they're a power users setup, and IMO should only be considered when the most powerful single GPU card doesn't give you enough grunt.
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The problem is that the fastest cards are usually hardly any quicker than the cheaper midrange cards, remember the 6800 GT - Ultra? that was taking the cake, so for starters if they want people interested in their high end cards they actually need to show a good performance increase over midrange cards. Not just a big price difference.
 
Personally, I think that the only time when SLI is truly worth bothering with, is when you have one of the cards already, and the same card comes along for a bargain.

That way you will get the boost with minimal outlay.


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Sillyness now, but... What I would like to know is this:-

All my SLI Mobos have a 16x PCIE Slot right...
So, I put in a Card and that runs at 16x
However, when I put in a Second card, the PCIE Slots switch to 8x
Why?
Is this why SLI is never double the speed... I mean, its not even close, its like 50% increase sometimes more but mostly less.
 
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Older SLI boards (before 680i and most of the 650 boards) only had x16 lanes that can be used by the GPU, so when you have 2 cards plugged in it would divert 8 to each.

My 750i board has the NF200 chip onboard as well so I get a full x16 pci-e 2.0 on each slot.

x8 doesn't hold any GPU upto the 8800GT (possibly the 250GTS) back really at all performance wise and only has a minor performance penalty on current generation cards.

The gains you get from multiGPU depend on a lot of factors, if your only playing at 1280x or 1440x type resolutions then you are unlikely to see more than 40-50% gains, whereas at 2048x res and turning up the FSAA I'm seeing atleast 70% gains in many titles and often ~90%.

There are times for SLI/CF but you really have to pick your moment...

i.e. 2x 8000GT could be had at one point for far less than a single 280GTX and would out perform it in most games at the time. Or if like me you play at a resolution over 1920x and like to max things out visually - then 1x top end card isn't good enough.
 
Rroff said:
The gains you get from multiGPU depend on a lot of factors, if your only playing at 1280x or 1440x type resolutions then you are unlikely to see more than 40-50% gains, whereas at 2048x res and turning up the FSAA I'm seeing atleast 70% gains in many titles and often ~90%.
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You are forgetting one crucial thing which most people seem to overlook, even though 70% gains might sound great, that is pretty useless if the overall FPS are something like 40. The higher you go the FPS go down quite a lot, so even though 70% sounds appealing it might actually not be so good.. so you get those gains yet the game still can run sluggish.

From what i have found the sweet spot is 1680 x 1050 - > 1920 x 1080 any higher is normally rubbish for newer games, that is going by benchmarks i have seen numerous times.

Puts me off upgrading to 24" monitors and higher personally, because then you have to have at least a top end single card if not then x2 to play the games at the native resolution otherwise you have to lower it then it can look a bit gritty in some games.
 
Not quite sure of your point... if your getting 40fps with a single card, SLI can get you back over 60fps. Sounds like a good deal to me.

I find that 260GTX SLI works a treat for resolutions over 1920x and under 2560x (you need a beast of a setup for that). Most games it keeps me in the ~100fps zone with max settings - which is what I want for playing online.

Only games I really have issues with are mass effect, crysis (which I don't play anyhow) and far cry 2. In mass effect multiGPU is screwed up and only works when your gun is holstered :( so it kinda sucks to see fps drop from 80 to 40 when you pull out your weapon. So I compromise there and use SLI AA so atleast I get a nice visual boost even with the lower framerate.
 
I am talking about SLI not a single card, the gains are good up to a certain point but the framerate can get below 60 when you go so far and then even though you get better frames with 2 cards it can still be quite slow.

Games like GTA IV and Crysis are a good example
 
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