ATI's X8xx CrossFire Graphics Arrive
by Derek Wilson on September 26, 2005 1:00 PM EST- Posted in
- GPUs
The Details of the Resolution Limit
The foremost issue we want to address in this section is that of the 1600x1200 resolution limit and the Single Link TMDS receiver on the CrossFire master cards. Much speculation has been passed around on the subject, and we wanted to get to the bottom of the issue. It is true that digital operation of the vast majority of ATI X8xx series parts are limited to single-link DVI speeds per display. ATI's position is that since most current X8xx series cards do not support dual-link output, a single-link receiver is all that is needed. This is a fine solution. The problem is that ATI is currently fixing maximum CrossFire resolution to 1600x1200@60Hz. While they have stated that it is technically possible for them to run resolutions at a similar pixel clock, they will not allow asymmetric timings between the TMDS receiver and the final output. In general, this means that any resolution larger than 1600x1200 will require a lower refresh rate than 60Hz. While this may be ok at HDTV resolutions or on a digital flat panel, CRT owners may elect to drop resolution even lower than 1600x1200 in order to play their games with a decent refresh rate. For an expensive, high end solution, a 1600x1200 60Hz limit is simply unacceptable.We asked ATI why the capabilities of the TMDS receiver on the master card must limit the resolution of CrossFire output to 1600x1200@60Hz. The answer is that scaling would diminish at higher resolutions due to the limited ability of the slave card to contribute in a balanced way. Granted, AFR (alternate frame rendering) modes could not be run and SuperTiling would have to be tweaked or dropped, but ATI does support 60/40 and 70/30 split frame load balancing as well. Enabling high resolutions only under their scissor mode should give some additional performance along with the ability to run at higher resolutions. To us, including the option for a customer to choose how the hardware he or she owns will work is absolutely a good thing. In our minds, a lower performing 2048x1536 is definitely better than not having the option at all. We would strongly urge ATI to consider adding such options in future driver releases if it is at all possible.
On top of that, multiple other options spring to mind on how resolutions could be increased. PCIe bandwidth could be used heavily to transfer screen data. NVIDIA has multi card configurations working with no direct physical link. In addition, it shouldn't be impossible for ATI to use both outputs on the slave card to send data to the master. Two single-link connections are the building blocks of a dual-link connection after all. But in the end, ATI stands behind their decision to implement CrossFire with a single-link resolution limit.
With maximum resolution limited, we must rely on features and quality to drive the decision to purchase a CrossFire setup. And the feature that ATI hopes will push CrossFire is their Super AA.
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waldo - Tuesday, September 27, 2005 - link
wow, that commment sure brought a lot of attention.I would agree that Thom's appears to be "outright-bought" in this article as they don't post the limitation of hte card at 1600x1200 @ 60hz, or at least not as clear as Anand, but they do make some valid comments that Anand's article didn't post either.
Perhaps they are targeting different audiences? No idea, but why are their numbers on par with the 7800 SLI in many situations? That sounds fishy somewhere.
DerekWilson - Tuesday, September 27, 2005 - link
Just to cover what others haven't yet --Adding an X8xx card to an R520 CrossFire card would either not perform well at all or would not work.
Personally, dual-GPU as an upgrade solution is not really a plus unless you are just deffereing purchase for a couple months while prices drop and your wallet heals from the first GPU purchase. If your personal upgrade cycle is a year or more, you'd be much better off just buying a new card from a new architecture.
Everyone else has pretty well hit it on the head. The 1600x1200 limit is a killer. We also have no availability and we are butted right up against the launch of ATIs next gen parts.
I wouldn't recommend SLI either -- as I said -- unless you want absolute maximum preformance. My recommendation may change to CrossFire after the R520 comes along. But who knows what the results of that comparison will be :-)
Mixed modes would perform slightly lower than the dual x850 xt setup and still at most 1600x1200@60 ... Yes, the X850 XT CrossFire does well in performance, but if I'm not going to recommend the X850 XT CrossFire, I'm certainly not going to recommend a mixed solution that will perform worse.
waldo - Tuesday, September 27, 2005 - link
I wasn't saying that you would recommend the other, but it would have been interesting for the readers (who attempt to be congiscent, autonomous beings, and only act at the whim and will of god Anand!) to be able to compare for themselves, per chance see what a mixed solution looks like as that is a selling point of ATI over Nvidia.I don't think SLI from NVIDIA is much of a solution. If you have $1k to shell out for graphics out of the starting gate, great. But you have to get the same manufacturer, the same card, and then the motherboard to match. But I won't be buying an ATI Crossfire setup just yet either.
JarredWalton - Monday, September 26, 2005 - link
Here's my personal take:1) If the 1600x1200@60 Hz problem doesn't bother you, that continue. For me, it's a deal-breaker.
2) Do you already own an X8xx card of some form?
3) Do you have a motherboard with two PCIe X16 slots?
4) Using the ATI Crossfire chipset?
If all of those are true, X800 Crossfire is worth consideration. Personally, 1, 3, and 4 eliminate it from contention. That said, this is current X8xx Crossfire we're looking at. We're not reviewing R520 Crossfire yet, and it will address at least the first point in some fashion.
Brian23 - Monday, September 26, 2005 - link
pwnedfishbits - Monday, September 26, 2005 - link
Yeah, accusing a site of corruption could seem like an attack.
1600 res limited to 60 hz is a deal-breaker for me right away. I can't tolerate playing at 60 hz for any length of time. I'm not a snob about this, it makes me physically feel ill. Pairing two powerful and pricey cards in one system should offer better, easily. I would not plunk down that kind of money to not be able to play at 16x12 when others do it at liveable refresh rates. Nvidia has better price-to-performance single and dual card solutions available right now. ATI should have the same shortly. The mega AA sounds great, but if as soon as you turn it on you say "I need to upgrade now," then what's the point? While the reviewed Crossfire is certainly nice in performance, there's better to be had for the money from both GPU suppliers. It would be irresponsible to recommend it at this time at the current price.
Now if there's a confluence of specifics where this setup makes gaming and financial sense to a handful of people out there, more power to them, they should enjoy this. For the teaming masses of readers though, you shouldn't be suprised by the lack of recommendation.
TrogdorJW - Monday, September 26, 2005 - link
LOL... attack an enthusiast site? Say it isn't so!How about the THG article? They review the platform as a whole, so that's a bit different. I won't comment much on their review, but consider a few points.
They have a page entitled, "Advantages Of CrossFire Over SLI" that reads like marketing hype, and yet they make no mention of the resolution limitation or "Advantages of SLI Over Crossfire". Clearly, they know the limitation exists - ATI hasn't tried to hide this fact, and the lack of any benches at higher than 1600x1200 is telling in and of itself. You do the rest of the math. (Also, some of the results are at best suspect.)
IMO, the writing of the THG article was a bit higher quality, but the content was far more suspect. They come off making everything sound rosey for ATI, and only a fool or a marketing department would believe that. ATI isn't dead yet by any means, but Crossfire is doing little for me right now. Did you realize that it's still not available for purchase at retail? Hmmmm.....
Oh yeah, Catalyst Control Center is pure garbage. Slow, clunky UI, memory hog, and causes as many problems as it fixes. Anyone that tries to tell me how great CCC is (i.e. THG) is immediately under suspicion.
fishbits - Monday, September 26, 2005 - link
Oh, I wasn't making a blanket statement that a review site couldn't be accused of corruption. Just that if you're going to do it, don't then wuss out and pretend it's not an attack :)My experience with THG is mostly second-hand, so I don't say much about it. That they chose to not mention the 16x12 refresh rate limitation, especially with all the debate over it before today, well... that's scandalous.
erinlegault - Monday, September 26, 2005 - link
The TechReport review was the best. Anand seems to give poor Graphics reviews, and definately not up to par with their CPU, motherboard and memory reviews. It must be the authors differences of opinion.overclockingoodness - Monday, September 26, 2005 - link
Could you clarify why Anand's video reviews suck? Just because Anand doesn't benchmark and show 100 diff. graphs of the cards based on the same architecture doesn't mean AnandTech's video reviews suck. TR is quite redundant from one article to another, if you didn't notice.