So recently, in another thread. People said a lot of bad things about SLI (For the uninitiated - Scalable Link Interface)
Like for instance “Almost no games utilize it properly”,
and “At doesn’t actually make much difference”
and “GTA IV doesn’t support it”.
and “SLI smells and it’s nose keeps running”
But surely for a game it is the easiest thing in the world to make use of - “For the next frame, use that other GPU I can see there”
And surely it isn’t even something the game has to worry about. Surely the decision on what GPU to use and whether to alternate frames between the two (or four if you have too much money and no life) is actually done in the DirectX or OpenGL drivers??
But I don’t know these things, so if you know a bit more about Directx/sli/graphics cards then I do then please educate me.
eta: And this graph (which admittedly must be biased) suggests that frame rates almost double…
(I actually found a different graph before that one, which showed actual frame rates and had Far Cry2 and FO3 on it, but I can’t find it now)
General consensus around my group of moderately-geeky PC builders is that it’s still too inefficient and widely unsupported. For the money, you’ll still get better performance by upgrading a SINGLE GPU rather than purchase two slower ones to parallel process.
Eventually I’m sure this will change - perhaps it already has an the years of useless SLI have jaded me. I will follow this thread with interest but without much hope that SLI will prove to be a good investment.
ETA: I’m also pretty skeptical of that graph. Why use relative framerates? I suspect the actual framerates are extremely low and that SLI works better with slow FPS and post-render processing (antialiasing and anisotropic filtering) turned way up. This chokes even expensive, modern cards and probably makes SLI look better than it really is.
Your last sentence is why I mentioned that I had seen a graph that showed actual frame rates. Because I’d asked myself the same question: Why use relative frame rates.
And I was hoping that in my case where the SLI is done with one ‘product’ in one slot (I have the GTX 295) they’d have more room to make it more efficient.
Even though I have the “absolute highest end” card on the market, it still isn’t a miracle worker. GTA IV still has it’s sliders at about one third away from the low end, and one particular physx demo has a noticable stutter when the number of objects is particularly high.
In fact so far, it hasn’t shown itself to be significantly better than the card it replaced (A single GPU Geforce 8800 Ultra)
eta: I’m just glad that what enabled me to purchase it was a semi-disposable income in the form of a will windfall. Overall I’m pleased about the purchase. And I look forward to the games that will better use this card.
Here are more frame rate charts than you can shake a stick at. The closest match to one of the NVidia stats I can find is HL2:Ep2, 1680x1050, 4xAA 8xAF. There, the 8800 GTS SLI got 78.7 fps, the single card 75.8. By contrast, for HL2:Ep1, 1600x1200, 4xAA 16xAF NVidia claim the SLI setup is almost twice as fast. Obviously they’ll be using different testing rigs so the results can’t be directly compared, but it still sounds like bollocks to me.
I don’t have a good understanding of the technical reasons, although I do have some idea, you’d be better served by searching a techie forum like [h] or anandtech.
But practically, I never recommend SLI to anyone. The practical gain of running 2 cards isn’t anywhere near 200% performance of one card - usually it’s anywhere from 90% (a decrease) to on the high end 130-140%. You’re always better off spending more money on a single card.
The possible exceptions are when you are an asshat with tons of money to blow and you want the absolute best possible performance - then sure, buy several of the highest end cards and put them in SLI. The other option is when you have an SLI motherboard anyway, and the card you bought a year ago is now pretty cheap, it may be a cost effective upgrade to buy a second card and throw it in there.
According to Wiki, Windows 7 is going to offer “support for systems using multiple heterogeneous graphics cards from different vendors (Heterogeneous Multi-adapter)”.
The thing about frame rates and details on graphics card performance provided by graphics card manufacturers is that they fudge… no that’s not right: they’re lies. Out and out fabrications. They’re rigged in the worst way possible.
Tom’s Hardware, on the other hand, runs a nice battery of tests with a variety of things. I still wouldn’t look at the 3dMark since more than one card manufacturer have set up drivers to have better performance on it than they do in real world applications (nVidia in particular on that one) but you can look at how a card behaves with different games and applications and get a better feel for it.
And you’ll note looking at the Tom’s Hardware charts that SenorBeef’s comment that you’ll see around a 30% to 40% performance increase as a maximum (and often much less than that) is accurate.
In pretty much every gaming application I can think of, the only reason to have SLI is to brag online that you have an SLI rig. To get anything out of it, you need to be running either multiple monitors, or an aboslutely huge monitor, and even there, as noted a above the increases are pretty minor for the cash you spend.