Revisiting SLI
Admittedly, we are skeptical of new technologies and products. After all, we think a healthy dose of skepticism is good since that means we reserve judgment until we saw proof to the contrary. When we first looked at what multi rendering has to offer with SLI, we were dismayed to say the least. From our experience, SLI doesn't always make good on its promise of performance. But at least, SLI have made good on the promise of quality, every time with every game.Seeing how successful NVIDIA is with SLI, the once critic of consumer multi rendering solution, rival ATI, decided they want a piece of the pie as well. Though reviewers generally felt ATI's Crossfire was late to do any good for their aging X800 and X850 cards, most agree the platform has the potential to rival SLI. With their latest X1K series of cards, Crossfire seems to deliver on both performance and quality. The only thing they need now is a much simpler setup, which already made its way to the mainstream parts.
Faced with this new threat from the Canadian manufacturer, NVIDIA answered with fervor in a two headed assault - Quad SLI and the GeForce 7950 GX2. Undoubtedly, these are meant for the high end market. However, the more interesting update from NVIDIA is actually under the hood of the updated GeForce 7600 and 7900 series. The GeForce 7600 family now comes with a much higher clocked core, 5 vertex shader units, 12 pixel shader units and 8 ROP units. In comparison, the GeForce 6600 series comes with 3 vertex shader units, 8 pixel shader units and 4 ROP units. On the high end of the spectrum, the GeForce 7900GTX is now running at a much higher clock, very close to ATI's Radeon X1900XTX. Most of the design of the GeForce 7800GTX is left intact (8 vertex shader units, 24 pixel shader units, 24 ROP units). NVIDIA is determined to win the mainstream parts battle.
We have reviewed these high end parts, but not the mainstream parts. It's not until this month, that we will be publishing our comparison of various GeForce 7600 cards. Since we now have several GeForce 7600GT cards in our lab, we think it's time to see what SLI has to offer with these new cards. Most of our experience with SLI have been with older cards, the GeForce 6600 and 7800GTX.
After looking at what Crossfire has to offer with both low and high end cards, we begin to see more than just potential in multi rendering solutions. We also mentioned that the performance limiting factor seems to vertex and polygon processing power. NVIDIA's latest products, the GeForce 7600 and 7900 series have all come with more vertex shader units than the previous generation. Having a much higher clock core will certainly not hurt them either. We're very interested to see whether this theory is true or not, so we put two GeForce 7600GT cards together for some SLI testing. We were pretty anxious to see if NVIDIA had a stronger offering for SLI with their GeForce 7600GT cards. Of course, it would've been more interesting to retest SLI with the high end GeForce 7900GTX, but we think both setups don't behave that much differently from one another.
At the same time, NVIDIA have also released a new reference driver, Forceware 91.31. No doubt, this latest driver is meant to support the recently launched GeForce 7950 GX2. For those who are not in the loop, the GeForce 7950 GX2 is actually two GeForce 7900 graphics cards put together into a single packaging that you can install on a single PCI Express x16 slot. The new drivers is updated with more game profiles, mostly to enable SLI support for these games. That makes it particularly interesting for our SLI testing.. However, after some time testing with these new drivers, we decided it would not be wise to use them for our performance evaluation.
Problems
Generally, we will use the more up to date drivers for an article or review. However, that is not the case here. For the time being, we will stick to Forceware 84.21 for most of our reviews. Although the new drivers offer some interesting features, like additional options for SLI multi rendering, we had a lot of issues and problems with Forceware 91.31 (and it's not the new control panel).
Starting with Forceware 91.31, NVIDIA have followed ATI's lead in many ways. It's not just the control panel, but also the handling of applications that made use of overlays, including FRAPS. So now, when FRAPS is active, you will not see changes to AA and AF settings from the control panel immediately applied, much like with ATI's Catalyst drivers. The safest way to enable AA and AF is to stop FRAPS first and then make the changes. Simple really. However, Forceware 91.31 have a very annoying bug regarding this behavior. The driver seems to fail purging the overlay and the screen after we exited a full screen application - like we usually do after benchmarking a game. So, after a benchmarking session, we can see the desktop, but can't interact with it. Or worse, all we see is a blank screen. There is a workaround to this: we simply have to switch to the desktop before quitting, stop FRAPS, then switch back and finally exit the game. This bug shouldn't affect ordinary users and gamers, but it really is annoying if you're trying to benchmark a game with FRAPS. Hopefully, NVIDIA will fix this in a patch or a new driver.
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