CrossfireX, it's a multi-GPU state which we'll cover a bit more in-depth on the next pages, pretty much you can utilize two or more graphics cards to work together and, hopefully, nearly double up on the game rendering performance.
As stated above, the Radeon HD 6850 and 6870 only have one CrossfireX connector, this literally means that you can place only two cards into a multi-GPU setup. While you might feel merely two cards is a limitation, we think .. it's just fine. As always we do not recommend you to utilize more than two GPUs in a PC anyway as you'd quickly run into driver issues, increased power consumption, more heat in the PC to deal with and well .. it's just that the overall compatibility factor starts to increasingly get complicated once you opt 3 or 4-way CrossfireX multi-GPU setups.
Two is fine really ... so with that said let's grab a reference 6850 and 6870 card from AMD, and then hook them up with some retail cards from HIS, to see where we end up performance wise.
I can already tell you this though, this was the first time ever we had no issues with drivers, and yeah, in most cases the CrossfireX scaling was just extraordinary good.
Oh you're interested now eh ? Good, let's head onwards into the review then.
Multi-GPU gaming explained -- Both NVIDIA's SLI and AMD ATI's Crossfire allow you to combine/add a second, third or even fourth similar generation graphics card (or in more GPUs) to the one you already have in your PC. This way you effectively try to double, triple or even quadruple your raw rendering gaming performance.
Think of a farmer with a plough and one horse. One horse will get the job done yet by adding a second or maybe even four horses, you'll plough through that farmland much quicker and (hopefully) more efficiently. As weird as that analogy sounds, that's roughly the same idea for graphics cards. One card can do the job sufficiently, but with two or more you can achieve much more.
So along these lines, you could for example place two or more ATI graphics cards into a compatible mainboard, or two or more NVIDIA GeForce graphics cards in SLI mode.
A Crossfire compatible mainboard is pretty much ANY mainboard with multiple PCIe x8 / x16 slots.
A SLI certified motherboard is an nForce motherboard with more than two PCIe xc16 slots or a certified X58 or P55 motherboard. If your motherboard does not have the SLI certification mentioned on the box, it's not SLI compatible. Keep that in mind.
Once we seat the similar graphics cards in the carefully selected motherboard we just bridge them together, with a supplied CrossfireX connector or in NVIDIA's case, a SLI connector. Then install/update drivers, after which most games can take advantage of the extra horsepower we just added into the system.
Multi GPU rendering -- the idea is not new at all... if you are familiar with the hardware developments over the past couple of years you'll remember that 3dfx had a very familiar concept with the Voodoo 2 graphics cards series. There are multiple ways to manage two cards rendering one frame; think of Supertiling, it's a popular form of rendering. Alternate Frame Rendering, each card will render a frame (even/uneven) or Split Frame Rendering, simply one GPU renders the upper or the lower part of the frame. So you see there are many methods where two or more GPUs can be utilized to bring you a substantial gain in performance.
Above two R6850 cards. One reference, one model from HIS. We use an unlocked engineering sample Core i7 965 processor and overclock it to 3.75 GHz for this particular system to find a good balance in-between power consumption, and some extra horsepower from the CPU to feed the GPUs data fast enough.
The advantage of a somewhat 6850 mainstream graphics card is that you'll only have one 6-pin power connector per card -- obviously you'll need two (2x 6850) or four (2x 6870) of them depending on what you are installing for a graphics card.
Power consumption
Lets have a look at how much power draw we measure with these graphics cards installed.
The methodology: We have a device constantly monitoring the power draw from the PC. We simply stress the GPU, not the processor. The before and after wattage will tell us roughly how much power a graphics card is consuming under load.
Our test system is based on a power hungry Core i7 965 / X58 based. This setup is overclocked to 3.75 GHz. Next to that we have energy saving functions disabled for this motherboard and processor (to ensure consistent benchmark results). On average we are using roughly 50 to 100 Watts more than a standard PC due to higher CPU clock settings, cooling, additional cold cathode lights etc.
With that in mind. Our normal system power consumption is higher than your average system.
Graphics card IDLE WATT FULL WATT
Radeon HD 6850 1024MB 176 278
Radeon HD 6870 1024MB 173 295
Radeon HD 6850 CrossfireX 186 393
Radeon HD 6870 CrossfireX 184 421
Recommended Power Supply
Here is power supply recommendation:
Radeon HD 6850 x1
On your average system the card requires you to have a 450 Watt power supply unit.
Radeon HD 6850 x2
A second card requires you to add another ~130 Watts. You need a 650 Watt power supply unit.
Radeon HD 6870 x1
On your average system the card requires you to have a 500 Watt power supply unit.
Radeon HD 6870 x2
A second card requires you to add another ~150 Watts. You need a 700 Watt power supply unit.
The more you overclock and tweak, the more power you will use, adapt to that, we always advise you to get a power supply that is more capable then you'll use, have some reserves, please, do not let a PSU be a limitation.
There are many good PSUs out there, please do have a look at our many PSU reviews as we have loads of recommended PSUs for you to check out in there. What would happen if your PSU can't cope with the load?:
bad 3D performance
crashing games
spontaneous reset or imminent shutdown of the PC
freezing during gameplay
PSU overload can cause it to break down
Final Words & Conclusion
We've been dealing with CrossfireX reviews ever since the beginning and surely a lot has changed over the years. The one recommendation we always gave you guys is to keep it simple at 2 GPUs maximum, as after 2 GPUs in a CrossfireX setup you quickly run into weird anomalies that can be irritating. AMD limited the 6800 towards 2-way Multi-GPU gaming as such was a very peasant experience. Most if not all games scaled just really well and the games that are a little GPU bound can scale at 1.9x ... which is very impressive to see.
So over the years Multi-GPU support has improved quite a bit, AMD still isn't up-to snuff at the level of NVIDIA though, multi-GPU supports still literally and directly remains the Achilles heel of ATI's Catalyst drivers. For years now we have been requesting user-based multi-GPU profiles. See when a new game comes out, multi-GPU support will not be supported by the Catalyst driver. ATI will always need to update this through drivers or downloadable profiles. What ATI needs to do is to allow the end user to make custom profiles per game. A small tip, renaming your game-executable towards a game title that is supported can, not always but often, help out.
Now we also do have warn you about the fact that multiple GPUs make more noise and heat inside your PC, so make sure you have some good ventilation inside your PC. Noise wise the R6870 was by far the best, you can expect plain silly old normal noise levels. The R6850 setup was more noisy but remained acceptable and not irritating, but it was borderline though.
Performance wise we see really good numbers, with two 6870 cards you'll see 27.800 points in 3DMark Vantage ( GPU P-score) and 23K5 points for the 6850 setup with two cards. That's sincerely high performance for cards in this price-range anno 2010. Relating that to games then, Dirt in DX11 scored 112 FPS at 19x12 8xaa/16xAF on the R6850 and 124 FPS for the R6870. Considering 60 FPS is all you need you would be future proof for a while alright.
Battlefield Bad Company 2 scores 89 FPS (6870) at 1920x1200 and 8xAA, that's just brilliant as that is a HUGE framerate with 1.9x performance increases. Fact is, you'll beat any single-GPU solution to date in terms of performance, and where the title really is multi-GPU savvy it'll kick in even harder.
Power consumption wise we don't see anything shocking either really, two 6870 cards peaked towards 275 Watt (graphics cards only) which is slightly above one GeForce GTX 480, these are all 'okay' values considering what we are doing.
So let's round things up, personally we always say stick to one or maybe two high-end cards as there is so much less driver fuzz to worry about. It's like this with ATI, once you pass 2 GPUs you'll often find yourself compromising a lot with new game titles versus multi-GPU support. And this is why today's tested products in 2-way CrossfireX mode work so well.
AMD really does needs to step it up a little more on better and even faster game profile support AND user based and created profiles, period. But sure, we also have to acknowledge here, ATI these days has very solid driver releases and release hotfixes and Crossfire support profiles to address to this concern. Credit where credit is due, the overall experience definitely is very interesting.
If you can pick up a second R6850 or R6870 for the right price and can life with some small catalyst driver incompatibilities (as in the future there's bound to be some), then sure .. we'd give a setup like shown today our two thumbs up. Its a relative easy and affordable way to double up on your game performance, if it's properly supported of course.
on XFX homepage they say u need atleast 600w for 2x6870, u say I'll need 700 w. I have 650w . will it work or is the computer only going to shut down ?
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