ATI's Multi-GPU Solution: CrossFire
by Anand Lal Shimpi & Derek Wilson on May 30, 2005 9:00 PM EST- Posted in
- GPUs
Final Words
Anyone need a quick recap?On the hardware side, ATI is launching a multi-GPU solution called CrossFire that can be added to any existing Radeon X800 or X850 graphics card when run in (to be verified) any motherboard with 2 physical x16 PCI Express slots. Also being announced is ATI's push further into the high end chipset space with their Radeon Xpress 200 CrossFire-Edition. This chipset can be used on motherboards for Intel or AMD solutions and will provide 2 x16 physical, x8 electrical PCI Express slots for CrossFire support. ATI CrossFire-Edition motherboards could also support NVIDIA's SLI cards if NVIDIA's drivers were properly adapted.
Setting up CrossFire on a system that uses selector ICs to allow BIOS control of PCI Express slots makes hardware installation easier than SLI. All that is required is to insert the graphics cards and then connect them with the external dongle. Of course, not all ATI solutions will include this feature. Using SLI, a bridge must be installed inside the case. This is a more elegant solution than a dongle, as it is out of sight, but switching from CrossFire mode to a 4-monitor setup is as easy as changing the way cables are plugged into the back of the computer. In order to use multi-monitor configurations on an NVIDIA SLI board, the SLI bridge must be removed. We don't consider the SLI selector card on the motherboard to be an advantage or disadvantage, as some of ATI's partners will be implementing selector cards or terminator cards rather than the BIOS configurable selector ICs. Really, both companies have pluses and minuses, and we leave it to the end user to decide whether the internal bridge or external dongle fits their needs better.
As far as software support goes, CrossFire will offer AFR, split frame, and supertiling rendering modes. Two new types of AA (called Super AA modes) will also be enabled by CrossFire: 8x/10x and 12x/14x with combine MSAA (the latter two modes including SSAA). We expect the same games (or types of games) to run using one of the three performance modes (AFR, split frame, or supertiling) and run well under SLI, while all games will be accelerated under any Super AA mode.
Had enough yet? Our initial performance test on prerelease hardware and drivers shows roughly 50 to 85 percent improved performance under Doom 3 from CrossFire. This indicates that we could see very good performance from CrossFire when it is finally released. Our initial tests aren't enough to draw any firm conclusions, especially in comparison to SLI performance, but we are looking forward to running a full suite of tests on the hardware.
The down sides of CrossFire mainly stem from the motherboard chipset. Either adding cost through the selector ICs or limiting convenience with a terminator card or SLI Style selector card is a tough call for vendors. Supporting two x8 electrical PCI Express slots does limit potential bandwidth and therefore, possibilities open to software developers. This isn't any better than what NVIDIA has to offer, so ATI need not worry much here. With vendors either using a ULi southbridge, or the (currently) buggy ATI southbridge, we may want to pay close attention to whose hardware is on the board. As far as the CrossFire card itself, we would prefer to see the 16 pipe CrossFire card not drop to 12 pipes when paired with a 12 pipe card (at least in split frame rendering). ATI's thinking is that the 16 pipe card would always be waiting on the 12 pipe, but in split frame rendering, giving more work to the 16 pipe card would help balance the performance. We just believe in people getting what they pay for.
If ATI can get CrossFire out to the market in good volume (for its potential demand), we could have an excellent alternative to SLI on our hands. ATI is also working on licensing CrossFire to SiS, so we may see SiS based boards with CrossFire support early next year as well. Exhaustive performance tests remain to be run, but from a feature standpoint, CrossFire looks good. We would like to see CrossFire offerings for Radeon cards slower than the X800, but other than that, we will have to sit back and wait for hardware to draw more conclusions.
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Pollock - Tuesday, May 31, 2005 - link
Looks interesting to me, at least so far. I'll agree that we still have to see how things turn out.Eug - Tuesday, May 31, 2005 - link
Crossfire? Meh. About 0.1% of the population will buy dual GPU setups. Crossfire is essentially just a marketecture exercise.The really interesting part is the H.264 acceleration, which will have much, much more impact for the general computing world than Crossfire.
nitromullet - Tuesday, May 31, 2005 - link
Interesting... They gave AT stock photos of a Intel based motherboard, but the benchmarking was done on an AMD rig. Anyone know if the chipset(s) support Athlon X2 and/or Pentium D?To the person that mentioned that Doom3 is not a good benchmark for ATi: My guess is that Doom3 is probably a good benchmark to use for this purpose. ATi is most assuredly GPU bound in Doom3, so any increase in GPU power will yield a positive result. Whereas in HL2 where ATi has really strong single performance, I would imgaine that the Crossfire rig is CPU lmited, so there is not as drastic of an increase.
Either way, Crossfire looks to be pretty interesting. Can't wait to see some in depth benches and some screenies of the super AA modes.
A request to AT: how about some benches in standard and widescreen resolutions. I know that SLI had compatibility issues with widescreen in the past, and it would be nice to know if those are still around and/or if Crossfire also suffers from this.
Nice article, especially with the limitation of not being able to run a full suite of benchmarks.
jiulemoigt - Tuesday, May 31, 2005 - link
So what about the fact the new mode does not work in OpenGL? I happened to love playing with directX api but knowing that half the engines will not be able to use the new filtering? I like the idea of the new chip they are putting on the board, I'm disguested most of the ATI stuff is marketing not hardware I have to develope for the hardware in peoples machines and the baises that people have toward tech and i'm getting sick of finding a new way of doing something not being able to use it because it only works on nvidia and ati bashes till they sorta get it working then they claim it's the best thing since sliced bread. Lets try and force nvidia and ati marking people to focus on what is there not what there side has.DerekWilson - Tuesday, May 31, 2005 - link
I suppose we should add a disclaimer to the statement about Super AA working with everything ...From what we *hear* from ATI, all games will work with CrossFire. This means that all games will work with at least one of the performance or quality modes. Even if a game doesn't work under AFR, split, or supertiling, it should work with Super AA ...
But we will have to test compatibility for ourselves.
Derek Wilson
porkster - Tuesday, May 31, 2005 - link
I can't see why they can't just use one PCIe card with a extra socket. Wheny ou ened to upgrade for more power then you buy just the chip and put the extra GPU chip in the socket to make a dual graphics card.SLI is a waste of time in that it's a direction in motherboard layout that isn't going to last, it's a dead end road for the future. So rather than was all the time developing cards that work in tandom, make the card to work with more GPU chip ont he same daughter board.
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AdamK47 3DS - Tuesday, May 31, 2005 - link
"all games will be accelerated under any Super AA mode"I hope Anandtech isn't pulling my leg here. I'd love to see Halo PC or Splinter Cell using AA. Currently no form of multisampling allows AA in these games. There are probably more games out there that have the same multisampling limitation, but these are the two I know of.
matthieuusa - Tuesday, May 31, 2005 - link
And should I had that investors seems to feel like ATI is taking its place back. NVDIA stocks already dropped 59 cents witht the announcement of ATI crossfire and R520 playback display...#37: totally agree, it is going to be a nice fight! If R520 is overall better than the G70, NVDIA will have to worry and counter it as fast as they can (which is going to be great for us).
matthieuusa - Tuesday, May 31, 2005 - link
I agree with #35. It is a little early to know which solution will be considered the best, even if it seems that ATI is bringing sone very interesting features along with their Crossfire. Not everybody care about playing Doom3 at 110 fps. I rather play at 80fps and have all the eye candies, and even more, since they are going to propose heavier FSAA.Since SLI and Crossfire will probably come to be close, it is going to see which one of the r520 and g70 will be the fastest with the most interesting features. But if ATI did as good with the R520 as they seem to have done with the Crossfire, they could take back the crown.
NVIDIA seems in hurry to put the G70 on the shelves, which seems kind of suspect, since there is are no real reasons to do so. They acually do have the most popular cards and the fastest configuration with SLI.
Did they heard about ATI R520 specs and fear to be at a disadvantage? Do they need two G70 to beat it?
Wait and See
#36 2PCI-E 8X -> that is exactly what SLI is right now with NVDIA.
Compositing Engine chip -> Do you remember the discussion about the PCI-E bridge implemented on GeForce 6 cards? Experience has shown no performance drop. Instead, in ATI's "SLI" solution, it seems even better since it is not part of the die -> less heat... It is not new to them, since there are using it in professionnals products
kyaku00x - Tuesday, May 31, 2005 - link
I think the next chipset king will be the one producing the best next-gen graphics cards. if NV70 is better performing than r520 then I wouldn't think that people are going to care about going ATI in the mobo department, but if r520>nv70, then nvidia may start losing the chipset market.this will be real interesting to watch, the first chipset war determined by graphics cards :P