ATI's X8xx CrossFire Graphics Arrive
by Derek Wilson on September 26, 2005 1:00 PM EST- Posted in
- GPUs
Final Words
The final verdict on CrossFire is very mixed. It is clear from our Game tests that SLI has a worthy competitor with parts in its price range at 1600x1200@60Hz and below. However, we have a hard time buying the idea that many gamers are going to shell out the money necessary for CrossFire with that kind of limitation. With cards like the 7800 GTX out there, and more interesting hardware from ATI coming soon, we are very inclined to recommend a single card upgrade. That recommendation is especially true for users who have 1280x1024 LCD panels or want larger than 1600x1200 resolutions from their graphics card.Fortunately, ATI has stated that near term future products will utilize dual-link TMDS receivers and allow users to run monitors like the 30" Apple Cinema display under CrossFire. While the TMDS communication is a very interesting solution to the multi GPU problem, limiting resolution based on available bandwidth just doesn't make sense to us. Scaling at the high end doesn't matter as much as compatibility. As long as bandwidth does limit output resolution, though, we are very happy to see ATI move to dual-link TMDS communication for their future parts.
It is very hard for us to support Super AA having seen the abysmal performance scaling we have shown here. With single cards using 4x and 6x AA more than doubling the performance of CrossFire with 8/10x and 12/14x AA, we can't understand why anyone would suffer the performance hit. In order for this to actually be useful, users would need to be monitor limited to 1280x1024 or below - in which case a CrossFire purchase is severely misplaced. At the high end, it is hard for us to believe that an increase in resolution to 1920x1440 (or even higher) would have as much of a performance hit. Maintaining a standard AA level on a high resolutions will likely provide better image quality than a low resolution with Super AA. It is also probable that performance would decrease less when scaling resolution beyond 1600x1200 than when enabling Super AA. Unfortunately, we don't even have the ability to test this theory properly with current hardware and drivers.
Despite exceptional performance at its target resolutions, we have to strongly recommend against the purchase of an X800/X850 series CrossFire card. (You also would probably need a motherboard upgrade for Crossfire anyway, making it even less attractive.) We have a hard time recommending all but the absolute top end NVIDIA 7800 GTX SLI as a viable solution. As an upgrade path, it makes generally much more sense to buy the next single card solution that comes out instead of spending money on older technology that won't scale as well, takes up a lot of space, eats up a lot of power, and likely incorporates fewer features. The only way we truly say that multi-GPU technology is a better solution than a similarly classed single card solution (even when upgrading from one card to two) is at the absolute highest end where there is no competition from a single card. And right now the king of the mountain is still a 7800 GTX SLI. But just how long will that last? Only time can tell.
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erinlegault - Tuesday, September 27, 2005 - link
Well because the 1600x1200@60Hz is only a limitation because of the existing x800 family of cards and not the x850 family and definately not Crossfire itself.
Pete - Wednesday, September 28, 2005 - link
It's a limitation of the X8xx esries, as they all feature single-link TDMS transmitters, and so the Master cards have single-link TDMS receivers. They should be good for more than 16x12@72Hz, per DVI spec; hopefully future drivers will up this a bit.Plus, didn't The Inq show a pic of 19x12@52Hz?
vijay333 - Monday, September 26, 2005 - link
Valid points, don't see why some people are ranking this post down.Pete - Monday, September 26, 2005 - link
I really like how concise and readable the first few pages are.I do agree that comparing XF directly to the "2nd gen" SLI of the 7800 is a little unfair, but it's still potentially useful to some people, and you obviously left in XF's direct competitors, 6800 SLI and a single 7800. This does take the article in the 'too much info' direction, as opposed to the first few pages' 'just enough' method.
I have a few suggestions and corrections, if you don't mind.
* Perhaps you could elaborate on how XF will remove the res/refresh limitation with the R520 line-ups dual-link TDMS transmitters? This is appropriate in terms of the 7800 SLI comparison, although who knows when X1800 XF will show up.
* On that note, I've read elsewhere that SuperAA is so unbelievably slow because XF is actually using PCIe (bandwidth- and latency-limited) lanes and then the "master" GPU (for inter-GPU communication and then to composite the image, respectively), and not the dongle and CE (as with "normal" XF operation). This will supposedly be corrected in a future driver, but (IMO) it's as big a shortcoming (however temporary) as the (permanent, hardware-imposed) resolution limit. And I'm quite skeptical about future driver fixes, though it seems essential that ATI solve this one.
* p.6, you write "pre" instead of "per."
* p.7, "worth" instead of "worthy."
Will you be examining these issues at Ibiza, or will you have time before packing your sunscreen? :D
(And no, I'm not ignoring you, I'm just an incredibly slow and unimaginative thinker at times.)
DerekWilson - Monday, September 26, 2005 - link
I did mention that ATI's next gen part should remove the limitations of the single-link TMDS somewhere in there ... I am unable to go into detail at this time.I'll have to follow up on the PCIe rather than TMDS angle. That would make some sense to me though. All the subsamples from a single pixel may need to be in the same framebuffer in order for ATI to perform proper AA on them. It may be that the gamma adjustment causes some problems with doing a straight blend between the two scenes. Of course, that's speculation about speculation, so I wouldn't put much stock in my musings :-) As I said though, I'll follow up on this.
I fixed my typos. Thanks.
Glad you liked the article. And where I'm going next sunscreen won't be of much use. :-(
Also, I didn't think you were ignoring me. I've actually been pretty busy myself lately, so I completely understand.
tfranzese - Monday, September 26, 2005 - link
I'd appreciate it if all graphs had units attached. Numbers are certainly not good if they don't have units attached.OvErHeAtInG - Monday, September 26, 2005 - link
Is it the mode scaling you're worried about?From p 6: "Our graphs show frames per second on the y-axis and AA mode across the x-axis."
The rest of the sideways-historam-thingies show fps. That is pretty standard.
OvErHeAtInG - Monday, September 26, 2005 - link
I meant histogram, not historam. D'oh! And yes, I realize it's not really a histogram. Bar chart ? Ah! Who cares.OvErHeAtInG - Monday, September 26, 2005 - link
Or watts for the wattage graphs. :)Stefan - Monday, September 26, 2005 - link
Shouldn't we be comparing the Crossfire to the 6800 Ultra SLI and not the 7800 GTX SLI?I thought ATi's new X1800 Crossfire was going to be the 7800's counter. Or am I mistaken?