Crossfire: ATI's Answer to SLI - Part 2
Both Crossfire and SLI took some news time the past weeks with NVIDIA and ATI making the annoucement of supporting Havok FX physics. NVIDIA was the first to announce their support, back at E3 and ATI has followed suit in Computex. In general we think this is a good thing, particularly with SLI. This means if you don't experience a performance increase with a Havok FX enabled game in SLI, you can either use SLI to have SLI AA or physics. At the moment, ATI certainly have the better offering here, because you can pair different cards - say a X1900 with a X1600 - one to do the graphics and one for the physics. God knows you don't want to use such a combination for graphics.However, what is a dissapointment is the two manufacturer's insistence to enable physics acceleration only on their own platforms - ATI with Crossfire and NVIDIA with SLI. Those who use Intel processors with Intel dual PCI Express x16 slots may get them (or may not). So, users with AMD processors most likely have to make a choice, it's either Crossfire or SLI. The only platform independent solution at this time is Ageia's PhysX and that hasn't impress many people, users and reviewers alike.
We all can guess why ATI and NVIDIA choose to only support physics accelaration with their own platforms, but it is dissapointing nonetheless. It's probably as dissapointing as having those dual GeForce cards, apparently you still have to use NForce 4 and 5 SLI series to use these cards at all. Thankfully, since both manufacturers support the same software (Havok), there will likely be no such issues with Havok FX enabled games (once they arrive).
Since there are no Havok FX enabled games that support physics acceleration in the market at this time, we'll have to evaluate each manufacturers' solution by what's possible right now - graphics performance and quality.
After seeing what Crossfire has to offer with the Radeon X1600XTs, we really want to know just how far you can go. Thankfully, we've managed to snag a Radeon X1900 Crossfire Edition and a Radeon X1900XTX for some Crossfire testing. Like we promised last week (actually that's two weeks ago - ed), we will not only be looking at what a pair of Radeon X1900 can offer in Crossfire mode in terms of performance, but quality as well.
In case you don't know, if you want to use two Radeon X1900 in a Crossfire setup, you'll have to put up with the Crossfire cable sticking out of the case. These high end cards still use the old version of Crossfire. Obviously, this has aroused some complaint from many reviewers and users - us included. After all, the Radeon X1800GT (and quite possibly the Radeon X1900GT) can be used in Crossfire mode without cables and a master card. Well, only ATI knows the answer to that, however we think there's a technical explanation for this. With dongless (and masterless) Crossfire, all card to card communication have to go through the PCI Express bus. The bandwdith used to send the second image (in AFR mode) to the first card can be very high (think 1600 x 1200 at more than 60 fps). That's true even if the two cards use full x16 slots. There's also the additional latency to account for. Since there's no bridge or internal connector like those present in GeForce 6 and 7 series of cards, ATI have to make do with an external cable. Since it's an external cable, that means its very susceptible to improper installation or worse, faulty parts and manhandling.
This article took longer than expected because of some problems we have with some of our testing procedures. Mind you, these are not technical problems concerning either the Radeon cards or the Crossfire motherboard. Unlike the two Radeon X1600XTs, you still need to use a Crossfire cable for the Radeon X1900. Like most external cables / connectors, improper installation can cause some distortion. When we did our preliminary testing with the two Radeon X1900s, there's a faded, vertical white line on the left side of the screen. This line is only noticeable at bootup (or desktop resolution changes). It's not necessarily distoring the screen, it's just simply annoying that it's present. After all, a Crossfire setup like this cost quite a lot of money and we certainly don't appreciate something like this. We also notice some flickering issues with some games. Once we make sure the cable is properly installed (the second time), most of these issues went away (or at least become less noticeable).
However, the most important problem to mention is image quality comparison, which we will elaborate.
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