Introduction

Four months ago, ATI officially announced their first multi-GPU solution called CrossFire.

Two months ago, we previewed and benchmarked it.

And today, ATI lifted their NDA on CrossFire performance with the Radeon X850 XT.

Contrary to what we were all led to believe, CrossFire cards are still not available, so today, we have little more than what we had two months ago when we previewed the platform.

Obviously, drivers have improved tremendously since we first benchmarked CrossFire, but as you will soon see, the platform still isn't entirely perfect. You will also find that CrossFire performance is decent, however plagued by an unfortunate GPU limitation limiting current CrossFire setups to a 1600 x 1200 maximum resolution.

The timing of today's NDA lift is curious at best, given that ATI's next-generation GPUs are literally just around the corner. In fact, given things such as the current 1600 x 1200 resolution, we honestly wonder why this performance introduction wasn't delayed until ATI's R520 launch.

Meanwhile, NVIDIA has steadily been improving the quality and availability of their SLI platform, which was announced over a year ago. Across the vast majority of their product lines, ATI is playing a seemingly never-ending game of catch-up. From the delayed release of the R520 to CrossFire, things haven't been looking up for ATI. Let's see if the trend continues here today.

The Details of the Resolution Limit
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  • erinlegault - Tuesday, September 27, 2005 - link

    quote:

    CrossFire is limited to a peak resolution of 1600x1200 at a 60Hz refresh rate. CrossFire relies on the single-link DVI output of existing Radeon X800-family graphics cards, and that connection tops out at 1600x1200 at 60Hz.


    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.
    Reply
  • 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?
    Reply
  • vijay333 - Monday, September 26, 2005 - link

    Valid points, don't see why some people are ranking this post down. Reply
  • 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.)
    Reply
  • 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.

    Reply
  • 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. Reply
  • 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.
    Reply
  • 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. Reply
  • OvErHeAtInG - Monday, September 26, 2005 - link

    Or watts for the wattage graphs. :) Reply
  • 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?
    Reply

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