The architecture in practice
The GeForce 6600 manages only one interface, the PCI Express, and so the first GeForce 6600 graphic cards and the one used for this test will be exclusively in this format.
Just a reminder; the PCI Express bus is a bus series that provides a doubled bandwidth compared to the AGP, from the system to the graphic card and from the graphic card to the system. The bandwidth goes from 2 GB /s to 4 GB / s. In addition, this bandwidth is bidirectional and cumulative, unlike the AGP. Finally the PCI Express is able to provide 75W to the graphic card instead of 40 W for the AGP and is more easily integrated to the motherboard.
In practice, however, the performance gain is limited. We have already discussed this issue in a previous article. So you don’t have to change to the PCI Express unless if you want to buy a GeForce 6600.
Is this choice definitive? No! NVIDIA almost covered every angle with the HSI. This chip, which equips the GeForce PCX (GeForce FX PCI Express), is also able to make an AGP bridge to the PCI Express. These bidirectional chips will allow NVIDIA to release the AGP format GeForce 6600 at the end of October.
SLI
Unlike the PCI Express versions, the AGP won’t have a SLI port. With this technology it is possible to connect two PCI Express NVIDIA graphic cards to combine their performances. Of course to use this capability you have to possess a card with two PCI Express 16x ports. This type of configuration will be more common with the release of the next nForce 4. This is very interesting for the mid-range line of products, because you will be able to buy a GeForce 6600 GT and another one later to use the two graphic cards side by side. Of course the cost of a bi PCI Express x16 motherboard also needs to be included.
Detonator 65.76
For this GeForce 6600 GT test we used the Detonator 65.76, on which the next official drivers should be based. Compared to the 61.77, performance gains were variable depending on the game. In our test replays with the GeForce 6800 GT, we noticed no improvement with Fifa 2004, Warcraft III or Colin Mc Rae Rally 04. Performance gains were 2.7% and 5.6% with UT2004 and Far Cry in 1600 x 1200 AA 4X/Aniso, 3% with Splinter Cell and 6 to 8 % with Doom 3. The most impressive gain was with IL-2: 20% in Excellent 1600 x 1200 4X/8X, 13% in Maximal 1600 x 1200, 34 % in 1024 4X/8X and 28% in 1600 4X/8X! We will update our top-of-the-line graphic card test as soon as NVIDIA releases official versions and ATI the final Catalyst 4.9 version. This shouldn’t be long.
Regarding performance gains observed in games, it’s generally not due to an innovation of a chip’s units. In our last test we mentioned filtering optimizations, or “compromises” integrated to ATI and NVIDIA’s drivers.
These optimizations come in two forms. The first is a new option called anisotropic sample optimization, accessible via the control panel. It “optimizes” the sample position for anisotropic filtering on all but level 1 textures. However, it is not the only optimization as you can see in this test with a fixed image of UT2004, less dependant on the CPU than our test scene in 1600*1200 Aniso 8x :
6600GT, 61.77, Quality, Optis off, 62.1 fps
6600GT, 61.77, Quality, Optis on, 73.9 fps
6600GT, 65.76, Quality, Optis off, 65.2 fps
6600GT, 65.76, Quality, Optis on, 72.3 fps
6800GT, 61.77, Quality, Optis off, 79.5 fps
6800GT, 61.77, Quality, Optis on, 91.9 fps
6800GT, 65.76, Quality, Optis off, 85 fps
6800GT, 65.76, Quality, Optis on, 95 fps
Unlike ATI, NVIDIA allows the total deactivation of these compromises except anisotropic filtering regarding angles. To make this change activate driver High Quality mode.
6600GT, 61.77, High Quality, 59.1 fps
6600GT, 65.76, High Quality, 59.1 fps
6800GT, 61.77, High Quality, 74.6 fps
6800GT, 65.76, High Quality, 74.6 fps
The equal performances obtained in High Quality mode show that the gain probably comes from a filtering compromise. There are two types of optimizations, the first one is documented, the second one isn’t. The latter permits an improvement of the 65.76 performances by 6.9% with the 6800 GT and 5% with the 6600 GT in quality mode and all optimizations deactivated in the driver panel control.
A closer study of screenshots allowed us to conclude that it’s probably due to a slight trilinear filtering modification not activated when using the color tool and the mips maps. In practice, the user won’t notice a difference, but it could be helpful if NVIDIA lets us know more on this optimization and gives us the possibility of deactivating it.
With more and more “compromises” comes the option for their deactivation. Luckily with NVIDIA this is already possible to deactivate these optimisations via the drivers, however a little more information on them would be nice. ATI first needs to start with giving us the option to deactivate them and then the information.
If 61.x Anistotropic Optimization setting had no effect on OpenGL (it forces the bilinear on textures other than 1 level in D3D), with the 65.x the equivalent "Anisotropic mip filter optimization" setting force the bilinear in OpenGL for all textures. It’s useless to mention that it shouldn’t be activated for good graphic quality...
