We proceed with our tests of "duets" of video cards based on GeForce 6800/6600.
In this part of the material we'll analyze the work of such tandems based on the new NVIDIA product – nForce4 SLI. ASUSTeK was practically the first manufacturer to release such production motherboards on the market, so we have carried out our tests on the basis of the A8N SLI Deluxe motherboard.
You can get more details about this motherboard from the corresponding article in the Motherboards section of our web site. I will just remind you that nForce4 was the first chipset to offer not only support for modern AMD solutions but also simultaneous use of two PCI-Express x8/16 video cards, which means that such motherboard can have two PCI-E slots.
Of course not all nForce4 chipsets support this feature, that's why the series: nForce4, nForce4 Ultra, nForce4 SLI. And only the last one supports two-slot video card solutions, and consequently SLI.
So, our testbed got a new look, it has become dark-brown (the color of the motherboard PCB) and acquired a fashionable illuminated cooler from Gigabyte.
The main heroes are the same, though – video cards :), so let's get right to them.
Actually, there is little sense in describing them, because we used the same accelerators as in the first part of our material.
Installation and Drivers
VSync is disabled.
A pair of GeForce 6800GT PCI-E video cards
A pair of GeForce 6600GT video cards
Note that the ASUS product provides for selection of motherboard operating modes: two video cards or one, this can be done with the help of a special module between the PCI-E slots, which resembles SO-DIMM. The module has two sides and works as a switch: insert it one side into the slot – the first mode is enabled, insert it the other side – the second mode will be enabled. If you need to activate two video cards, each one will operate as PCI-E x8. If you switch to a single video card mode, the video card in the first slot will get PCI-E x16.
There is an additional power connector right over the first PCI-E slot: you should plug the cord from the power supply unit into this connector in case of SLI mode (this is a requirement set by designers to increase operating stability).
The first slot is marked blue, a monitor is connected to the video card inserted to this slot. Another nuance: the slots are placed farther from each other than NVIDIA intended, so the SLI connector from this company will not do in this case: there are two slots between these video cards instead of only one. However ASUS designed a similar proprietary SLI connector (synchronizer) and ships it with the motherboard (you can clearly see it on the photos).
Test results: performance comparison
We used the following test applications:
Unreal Tournament 2004
TR:AoD, Paris5_4 DEMO
Here is a striking example of a test, for which NVIDIA drivers were fine tuned. The lion's share of performance in this test is up to GPU, and practically pure SM2.0, which makes it easy to fine-tune software.
The results are practically similar to the previous ones. Obviously, the performance turns on the system resources and that does not allow large yield from SLI (but these are the conditions. And potential buyers of such systems shouldn't forget about it: having paid about 1000 USD for a couple of video cards, you will not necessarily get stunning performance gains even in the heaviest modes, because the lion's share of games will turn on the capacities of CPU and FSB long before the video card capacities are depleted).
And this test demonstrates what happens if the game depends much on CPU (or a separate game scene) or when everything is up to geometry calculations, which are not duplicated by SLI. So the effect of SLI usage is minimum here. Moreover, there are many percentage minuses and thus defeats.
Half-Life2, ixbt01 demo
The picture is repeated again. Yes, the SLI effect is present, but it's weakened by factors, where SLI is powerless. It's geometry and system resources. Even with 2400 MHz Athlon 64 (this is quite an expensive processor). But the picture gets even bleaker for both SLI tandems, when we see that X850 XT PE, which is certainly less expensive, is often more powerful. To say nothing of the pair of 6600GT, which was completely defeated by X800 XL.
Half-Life2, ixbt02 demo
I think there is no need in comments, this test provided almost no good news for fans of new superpowerful SLI systems. There are some gains, but on the whole the competitors from the Canadian manufacturer turned out stronger.
Half-Life2, ixbt03 demo
The same picture. And the situation is even worse. On the whole it's obviously useless to buy a SLI system for Half-Life2. Probably the same applies to other games based on this engine.
Perhaps NVIDIA will improve its drivers, but still, the game is so CPU-dependent that even the Californian programmers can do nothing about it.
That stiffens the spirit of SLI fans! Yes, this test again demonstrated huge performance gains from SLI reaching doubled values. It's DOOM III, you know – favourite child of the American manufacturer, and its drivers are fine tuned. :) And the advantage over ATI competitors certainly reaches incredible values! We'll see what results will be demonstrated by games based on this engine. But the picture looks optimistic for SLI so far.
Quite naturally, this test and DOOM III are the first priorities to fine tune the drivers for. That's why we see brilliant SLI results, which should be ideally the case for each game not turning on CPU and geometry.
So, final conclusions on two large analyses.
The main conclusion: SLI operates well and is even very effective in applications, which do not turn on CPU and FSB capacities, and also where geometry calculations generally do not slow down GPU performance.
There is still much criticism about the quality. The drivers are far from perfect. Especially it concerns 1600x1200 resolution, where the screen sometimes displays a cacophony of colors instead of the sky image, for example.
Detailed analysis of the performance in time graphs from the first part of our review by the example of 3DMark05 Game1/2/3 made it clear that, for example, Game3 uses the frame-by-frame switching between the cards (as in ATI MAXX between the chips) and so instant FPS changes at great amplitude. That's why I think that I have made the wrong conclusion in the first part about this mode being unavailable. This mode is available, but it can be enabled/disabled only by the driver, users cannot do that.
Fourthly: Obviously, the SLI efficiency completely depends on the given game support by the drivers. That is SLI does not operate well absolutely in all games. The process complexity has grown by orders since 1998 and so very much is up to software. Consequently, we are waiting for guys from NVIDIA to fix the existing bugs and to improve SLI efficiency where possible.
And the last thing: it's clear that to buy two 6600GT video cards for this mode is often inexpedient, X800 XL sometimes turning out advantageous. It's up to users' tastes. It is reasonable when your purchase of 6600GT and then of the second card is only an intermediate solution before you buy a couple of 6800GT or 6800Ultra. Motherboards on nForce4 SLI promise to be not that expensive, you don't have to change RAM (the same DDR400), processors are quite affordable, so these are all pros for SLI. One should also note that the new platform was stable, we had no problems or gripes about it, which is a pleasant surprise.
In our 3Digest you can find more detailed
comparisons of various video cards.
Theoretical materials and reviews of video cards, which concern functional properties of the GPU ATI RADEON X800 (R420)/X850 (R480)/X800XL (R430)/X700 (RV410) and NVIDIA GeForce 6800 (NV40/45)/6600 (NV43)
We express our thanks to
for the provided devices for the testbed
Andrey Vorobiev (firstname.lastname@example.org)
December 21, 2004
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