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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yacoub - Tuesday, May 31, 2005 - link
Is it just me or do several things about this scream "bottleneck" and "latency"? The 2PCI-E x8 slots instead of x16 slots. The extra Compositing Engine chip. The ability to pair different cards such that it will drop clock speeds and/or pipelines to sync them up. The lack of direct chip-to-chip interconnect.I'm curious to know just how much performance gain is realized if you pair, say, an X800XL and an X850-something, over just the X850-something. And also how much bottleneck and latency there is in this implementation over the NVidia offering of SLI.
The only upside I can see is cost/upgrade since a user can own an X800-based card (assuming they have a Crossfire compatible motherboard) and go out and buy an X850-based card later and use BOTH cards together (assuming they are both Crossfire-capable cards). Then again with those assumptions I'm not sure it's truly any more cost-effective. =\
LoneWolf15 - Tuesday, May 31, 2005 - link
As usual, the fanboys of both sides come to the show to spout their comments.For everyone saying "Man, you have to buy a Crossfire that matches your card, and throw it away when you upgrade"...umm, don't you have to buy two of the exact same matching card for running nVidia SLI, and if you wish to upgrade, you have to sell both? Doesn't sound that different to me. One thing I think a lot of current ATI owners will be happy about is that they won't have to get rid of a card they already own and buy two of a new one; they can just buy a single Crossfire card (and of course a mainboard).
On the other hand, to those thinking ATI has now "0wned" nVidia, it is WAY too early to tell. The solution looks promising, but if you have to sacrifice mainboard performance (i.e., SATA hard disks, memory bandwidth, etc.) it may be a hard sell. Benchmarks in Doom 3 are also not the end-all be-all. We'll have to wait for a more comprehensive performance review, including DirectX benches, and performance/quality with older games using this new AA method, as well as game compatibility reports. We'll also need to know what TRUE pricing is (we've seen claimed pricing vary quite a bit from what it has turned out to be at product release in the past two years).
Do I hope it will beat nVidia's solution? You bet. I like ATI, but even more I like competition that drives the industry. Do we proclaim ATI the winner/loser on this one? Heck no, it isn't even a purchaseable product yet.
ElMoIsEviL - Tuesday, May 31, 2005 - link
23 - They ran Doom3.It's not an ATi game at all as we all know. And it still does REALLY well. And it's not in release stages yet.
;)
ElMoIsEviL - Tuesday, May 31, 2005 - link
hehehehe.. it's better then SLi... heheheheFigures, all the NV on here prolly aren't too happy today.
I can't wait to test out the new AA modes.. :)
vertigo1 - Tuesday, May 31, 2005 - link
This is insane, who on earth will buy this?!JarredWalton - Tuesday, May 31, 2005 - link
30 - Yes. The PCIe bus likely provides slower performance, as it is used for lots of other things (like communication between the CPU, RAM, and GPUs). I believe NVIDIA SLI works without the dongle but at slower speeds - at least, I heard that somewhere, but I haven't ever had an SLI board so I can't say for sure. Anyway, since DVI is a digital signle, using DVI in/out seems about as good as the SLI bridge - at least in theory. Now we just need to wait and see how theories pan out. :)Jalf - Tuesday, May 31, 2005 - link
I was under the impression they were going to use the PCI-E bus for transferring data between the cards. Is the external dongle going to handle that instead?Murst - Tuesday, May 31, 2005 - link
I really don't see how the xfire is better than sli based on hardware compatibility. Sure, you don't need the exact same cards, but you will likely buy only one x850 type card per x850 xfire. It would be extremely unlikely that someone upgrades from x850 xt pro -> x850 xt pe.Basically, in the end, you will buy a specific xfire tailored to your gfx card, and throw it away with the next generation of cards.
gxsaurav - Tuesday, May 31, 2005 - link
Great this just means more heat, man, even a single 6800 nU playes everygame fine, while running coolViRGE - Tuesday, May 31, 2005 - link
#21, yes it is. This is what hurts ATI the most, Nvidia already had 4 release cycles of experience with motherboards(2 of those being highly popular, highly recommended boards) before attempting SLI. ATI has a previous launch for a board almost universally ignored. I would not use an ATI board at this time, so I would also not consider CrossFire. ATI needs to get CrossFire working on Nvidia's boards to have a fighting chance this round.