The New Face of CrossFire

There haven't been any changes to the way CrossFire works from an internal technical standpoint, but a handful of changes have totally revolutionized the way end users see CrossFire. NVIDIA's SLI approach has always been fundamentally better from an end user standpoint. Internal connectors are cleaner and easier to use than ATI's external dongle, and the ability to use any X1950 Pro in combination with any other X1950 Pro is absolutely more desirable than the dedicated master card approach. ATI has finally done it right and followed in NVIDIA's footsteps.

At the heart of the changes to CrossFire is the movement of ATI's compositing engine from the card onto the GPU itself. This does add cost to every GPU and thus every graphics card, but the added benefits far out weigh any negatives. In early versions of CrossFire, digital pixel information was sent between cards using TMDS transmitters (the same transmitters used to send display information over DVI and HDMI). While this format is fine for displays, it isn't as well suited for chip to chip communication.

With the compositing engine built into every GPU, ATI is now able to send pixel data through an over-the-top NVIDIA style bridge directly to another GPU. This also eliminates the necessity of a TMDS link for use in transmitting pixel data. ATI hasn't talked about what type of communication protocol is used between the compositing engines on each chip, but we suspect that it is a little lower speed than NVIDIA's 1GHz connection. ATI is using a higher bit-width connection split into 2 12-bit parallel channels. At full capacity, ATI states that these connections can support resolutions of up to 2560x2048, but that communication doesn't happen any faster than the old style TMDS method.

ATI did make it clear that even though this incarnation of CrossFire supports a higher resolution than we are currently able to test, it won't necessarily run well. Of course, we'd much rather see a situation where we aren't limited by some technical aspect of the hardware. The first incarnation of CrossFire was quite disappointing due to its low maximum resolution of 1600x1200.

One of the oddities of this multi-GPU implementation is the splitting up of the connector that links the GPUs. Both are required for the driver to enable CrossFire, but only one is technically necessary. As bridges will be bundled with graphics cards, everyone who purchases 2 X1950 Pro cards will have two bridges. This eliminates the need for end users to buy bridges separately or rely on them shipping with their multi-GPU motherboard. When pressed further about why two connectors were used, ATI asked us to envision a system with 3 or 4 graphics cards installed. With 2 channels, cards can be easily chained together. This does offer ATI a little more flexibility than NVIDIA in scaling multi-GPU configurations, but it is also a little more cumbersome and offers more small parts to lose. Overall, though, the 2 channel configuration is a good thing.

Now that we have a chip built specifically for the $200 price point with a robust, full featured, CrossFire implementation, we are very interested in seeing what type of performance ATI is offering.

RV570 and the Demise of the X1900 GT The Test
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  • Zoomer - Thursday, October 19, 2006 - link

    Is this a optical shrink to 80nm?

    Answering this question will put overclocking expectations in line. Generally, optically shrunk cores from TSMC overclock to the about the same as the original or perhaps slightly worse.
    Reply
  • coldpower27 - Friday, October 20, 2006 - link

    Well no as this piepline configuration doesn't exist natively before on the 90nm node. It's a 3 Quad Part, so it's basedon R580 but has 1 Quad Physical removed as well as being shrunk to 80nm. Not to mention Native Crossfire support was added onto the die. Reply
  • Spoelie - Friday, October 20, 2006 - link

    Optical shrink, this is 80nm and the original was 90nm. You're normally correct because the first optical shrink usually does not have the same technologies as the proces higher up (low-k and SOI for example, this was the case with 130nm -> 110nm), but I don't think it's the case for this generation. Regardless, haven't seen any overclocking articles on it yet so I'm quite curious. Reply
  • Spoelie - Friday, October 20, 2006 - link

    oie, maybe I should add that it's reworked as well, so both actually. Since this core didn't exist before (rv570 and that pipeline configuration), I don't think that they just sliced a part of the core... Reply
  • Zstream - Tuesday, October 17, 2006 - link

    Beyond3D reported the spec change a month before anyone received the card. I think you need to do some FAQ checking on your opinions mate.

    All in all decent review but poor unknowledgeable opinions…
    Reply
  • DerekWilson - Wednesday, October 18, 2006 - link

    Just because ATI made the spec change public does not mean it is alright to change the specs of a product that has been shipping for 4 months.

    X1900 GT has been available since May 9 as a 575/1200 part.

    The message we want to send isn't that ATI is trying to hide something, its that they shouldn't do the thing in the first place.

    No matter how many times a company says it changed the specs of a product, when people search for reviews they're going to see plenty that have been written since May talking about the original X1900 GT.

    Naming is already ambiguous enough. I stand by my opinion that having multiple versions of a product with the exact same name is a bad thing.

    I'm sorry if I wasn't clear on this in the article. Please let me know if there's anything I can reword to help get my point across.
    Reply
  • Zoomer - Thursday, October 19, 2006 - link

    This is very common. Many vendors in the past have passed off 8500s that run at 250/250 instead of the stock 275/275, and don't label them as such.

    There are some Asus SKUs that have this same handicap, but I can't recall what models that were.
    Reply
  • xsilver - Tuesday, October 17, 2006 - link

    any word on what the new price for the x1900gt's will be now that the x1950pros are out?
    or are they being phased out and no price drop is being considered?
    Reply
  • Wellsoul2 - Monday, November 06, 2006 - link

    You guys are such cheerleaders..

    For a single card buy why would you get this?
    Why would you buy the 1900GT even after the
    1900XT 256MB came out?

    I got my 1900XT 256MB for $240 shipped..

    Except for power consumption it's a much better card.
    You get to run Oblivion great with one card.

    Two cards is such a scam. More expensive motherboard..power consumption etc.
    This is progress? CPU's have evolved..
    It's hard to even find a motherboard with 3 PCI slots..
    What a scam! Where's my ultra-fast HDTV board for PCI Express?
    Seriously..Why buy into SLI/Crossfire? Why not 2 GPU's on one card?
    Too late..You all bought into it.

    Sorry I am just so sick of the praise for this money-grab of SLI/Crossfire.

    Reply
  • jcromano - Tuesday, October 17, 2006 - link

    Are the power consumption numbers (98W idle, 181W load) for just the graphics card or are they total system power?

    Thanks in advance,
    Jim
    Reply

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