9 replies to this topic

[AnchisesGamer]

which would be better?

[Sen]

2 x 2Gb = 2Gb. The memory does not "stack".

To reiterate this so there is no confusion, you do not get 4 Gb running 2 x 2Gb cards.

This does NOT mean that 2 cards will not outperform the one card, but as you'e given no model numbers, it's impossible to say 100%.

[Catamount]

On paper, 1 4GB GPU, in practice, well... 1 4GB GPU, but not for the reason you may think.

You see, if you use two 2GB GPUs, you don't get the memory of both. Crossfire and SLI only use the framebuffer of the master card, so for your two 2GB cards, you get... 2GB. However, that's not really an issue. In most gaming situations, even 1GB is more than enough (basically, it's more than enough for 1080P for the foreseeable future), so it's highly doubtful that the difference between 2GB and 4GB will ever be meaningful withing the lifetime of the card(s). That said, you should always, always, always shoot for one powerful card over two slower ones. It's easier to wire for, the power draw is better, and most importantly, you don't have to deal with microstutter.

I wouldn't go as far as to say avoid Crossfire and SLI -including dual-GPU cards- at all costs, but it's not far off. The tradeoffs are big, and MS almost entirely overrides the performance advantage. Two cards are not meaningfully more responsive than one running at half the framerate; benchmarks might tell you you're going faster, but the playability will not drastically increase, because the increased latency keeps you from getting any increased responsiveness. The only time I'd recommend getting two cards at all is if it's impossible to get one that's powerful enough to suit your needs. Also, even getting one card, there's really no need to get a 4GB GPU, so if a model with less memory is around for the same performance, save the money and energy use and just get a smaller frame buffer (unless you plan on running, like, 3 2560x1600 monitors)

Edited by Catamount, 27 November 2012 - 08:29 PM.

[Sen]

Actually scaling on crossfire is fairly substantial. That's not to say that any card with 4Gb wouldn't beat. . say. . a pair of 6970s, but it REALLY depends on the cards.

Ease of setup, the higher powered single card is the win.

And. . wtf is microstutter? are we back on the 9.x Drivers? >.> I haven't microstutter since Burning Crusade ;D

[YellowDragon]

GPU memory does not stack with crossfire or dli configuration you only get the gpu vram of the master card which in the case of dual 2gb card is 2gb. Though unused vram provide no net benefit to fps unless you are reaching the full capacity of the vram. For instance most games at 1080p will never hit that 2gb frame buffer so a 4gb card would be worthless in a single monitor setup though if you are running 3d surround you would need more vram to drive multiple displays. What does matter in terms of fps on a single monitor is the GPU in the card and the speed its running at. I would recommend one powerful card over two weaker cards since few games are properly optimized for multi gpu setups. however if you have the cash and you drop in the highest end video card you can find and you want more power feel free to drop in another if you wish lol.

[RFMarine]

usually video card memory size is a poor indicator of performance.

if you are old enough you may remember the 512mb geforce 9800gt which totally outclasses the 1 mb geforce 9400


a noob friendly rule of thumb way of finding out which GPU to buy is to simply set a budget, get several models within that budget and google for benchmarks. the faster the benchmark usually the faster the card

Edited by RFMarine, 27 November 2012 - 10:02 PM.

[DV McKenna]

TLDR Version

Single - Dual Monitor gaming = 2GB
Tri Monitor + = 4GB to be on the safe side.

[Catamount]

Sen, on 27 November 2012 - 08:39 PM, said:

Actually scaling on crossfire is fairly substantial. That's not to say that any card with 4Gb wouldn't beat. . say. . a pair of 6970s, but it REALLY depends on the cards.

Ease of setup, the higher powered single card is the win.

And. . wtf is microstutter? are we back on the 9.x Drivers? >.> I haven't microstutter since Burning Crusade ;D

I'm afraid you've been misinformed. Microstutter has gone nowhere. SLI doesn't suffer it as badly as Crossfire (demonstrated here), but it also doesn't scale as well (~60% for 2 cards, instead of ~100%), so you get the same almost meaningless performance increase. If all you want to do is watch benchmarks play, then sure, at 60fps it's reasonably smooth, but the input lag introduced still makes the game play like it's going at 40fps, which makes having the second card almost pointless. That's why a couple days ago I finally traded my two 5770s for a single heavily OCed 5850; I lost about 5% performance (as measured by 3dMark11), but basically doubled the actual responsiveness of games, even at higher fps. Same fps, substantial upgrade. I made a BIG mistake not just paying the $100 and getting a 5870 instead of two 5770s when I built that comptuer, but oh well, live and learn.

At lower fps microstutter gets so bad, it even visibly chunks video. Run 3dMark or Heaven, and get those two Crossfired cards down to 30fps or less, and then compare them to a single card getting the same fps. The single card will look like it's going twice as fast because of MS.


Here's BF3 suffering MS at 30fps

https://www.youtube....h?v=MMPFfjupeq8

Here's a more visible example

https://www.youtube....h?v=zOtre2f4qZs


Past 40-50fps (that number purely from my own experience, it might vary for you), non-interactive video appears to stop suffering MS, but input lag stays bad. Again, this is the "responsiveness" of games, and it's something that, sadly, can't be demonstrated with a youtube video. It's also something you get "used to" with a Crossfire/SLI system, or at least I did playing with two 5770s for almost 3 years, but that's like saying you get "used to" low fps. It's still a huge difference moving to a single-GPU system. Moving to playing a 149kph Jenner with a single faster GPU vs two slower ones for the same framerate was probably the best thing I never did for MWO.


As an odd caveat to all of this, though, 3 or 4 GPUs (tri/quad xfire/SLI) do not suffer this problem nearly as badly, barely at all, in fact. The above Tom's Hardware link shows that. Why? I have no idea. Maybe somehow having more GPUs makes it more likely that one of them will finish the frame at the proper interval, or something, but it's more likely that I'm just talking out of my *** there. The why goes well beyond this poor bio major's knowledge of computing, I just know it does. Still, getting 3 or 4 GPUs is a complex and expensive proposition when one can just get one fast GPU and avoid all this headache altogether.

Edited by Catamount, 28 November 2012 - 10:26 AM.

[Hakkukakt]

hello ... just for exemple ... on tri screen 27" 5880x1080 no 3D ... MWO use 1.5 Go Vram on my GTX680 4Go ...

so if you often update your CG ... go for a 2 Go ... if you will take for a long road in futur .... go for 4 Go ....

[DegeneratePervert]

Gonna go ahead and weigh-in here. The single 4GB card will generally give you fewer problems than two 2GB cards, since you always get the same performance and don't have to rely on crossifre/sli drivers. As it has been mentioned before, the memory pool of cards in sli/crossfire does not stack.