NVIDIA GeForce 7800 GTX GPU Review

7800 GTX Features

We have already looked at how NVIDIA designed the new G70-based 7800 GTX GPU to be the most powerful consumer-level vertex and pixel processing chip on the planet.  But NVIDIA didn’t want to stop there and looked at how else they might improve the user’s experience in the world of PC gaming by introducing a couple of new features and enhancements to the core.

First up is a feature NVIDIA has dubbed Transparency AntiAliasing.  This feature addresses a problem that has been brought up by many of an image quality analysis called the “alpha texture problem.” The issue involved the inability for all past generation hardware to support antialiasing of any kind on the interior of a texture mapped object.  For instance, when a game designer makes a fence, they create a single polygon and then apply a chain link texture to it in which much of the texture has its alpha setting enabled.  When the renderer sees that the alpha channel on a texture pixel is enabled, it is deemed to be transparent, thus allowing the user to see behind and forcing the GPU to render the details seen through it.  However, since there are no edges along this hypothetical fence, current antialiasing techniques didn’t improve the alpha texture’s appearance and this stood out in many instances.  To see for yourself, enable 4xAA on Half-Life 2 and load up any map with a fence in it and you’ll see what I am referring to.  I have a detailed look at the feature on later pages to see the image quality difference.

NVIDIA’s release 75 driver and the GeForce 7800 GTX are able to detect the alpha setting on the texture and then apply a new AA algorithm that samples the interior of these textures to provide a better image with fewer of the ‘jaggies’ we all despise.  Both multisampling and super sampling options are available in the Rel75 driver and both have positives and negatives.  For one, the super sampling method is actually much more processing intense as it does a full run of all the calculations and texture fetches four times, while multisampling does an estimate on the shaded color.  In most cases, multisampling is acceptable and provides enough performance benefit to tip in its favor of supersampling.  There is at least one case where this doesn’t work out, but we’ll see that later.

High Dynamic Range lighting is another feature that NVIDIA has included in the 7800 GTX.  While it was an option on the NV40 as well, performance has been increased substantially this time around to the point where playing games with it enabled might be worth a look. 

For those unfamiliar, HDR is the method of attempting to map the entire spectrum of brightness that light has and the human eye can perceive in a much more realistic way than the current 8-bit lighting system uses.  The 7800s new higher precision FP16 floating point render targets allow for the HDR to be rendered more efficiently and thus gives the game the opportunity to provide more realistic lighting in games. 

I have a section after our initial benchmarks that looks at HDR performance increases from the 6800 Ultra to the 7800 Ultra as well. 

PureVideo has been improved with the release of the 7800 GTX as well; gone are the days with the flagship GPU having crippled video support!  Inverse 2:2 pull-down is now supported as well as a 3:2 to answer the cries of many overseas.  And while ATI was heavily pushing their support for H.264 accelerations in their upcoming R520 core, NVIDIA claims to have support for that as well.  High Definition video decoding performance has also been improved, but mostly due to the additional power of the extra pixel pipelines of the G70, not because of any fundamental changes to the PureVideo core itself. 

We’ll evaluate HD decoding performance later.

SLI is still very much a part of the G70 core and the 7800 GTX product launch, and you’ll see benchmarks for both single and dual GPU setups in our review.  There are some minor changes to the SLI setup and configurations options that are being announced with the 7800 GTX, but aren’t directly tied to it, so read the next page for a look at the Release 75 and 80 driver information. 

Finally, we come to the power usage of the 7800 GTX.  While it has been hinted at several times, you may have been dreading to hear the power supply requirements for this new 300M transistor chip.  Have no fear though, the 7800 GTX actually uses LESS power than the 6800 Ultra does.  The single slot cooler on the card pictured on the first page should have tipped you off, but I’m not going to blame anyone for fearing the worst.  But in fact, the 7800 GTX uses approximately 10-20 watts less power than the NV40, thanks to some insightful engineering. 

Much like the newly released dual-core Athlon 64 X2 processors, a lot of work went into the G70 to improve the performance and keep the power consumption low.  The G70 heavily depends on clock gating to keep its power low and as such you’ll see that the idle power of the 7800 GTX is lower by a wider margin than it is when under a full load.  And of course, if you can lower the power used AND increase the performance, you are guaranteed mathematically to have a better performance per watt part than in previous generations.