HD Decoding and Overclocking

High Definition Video Decoding

Since just before the release of the NVIDIA PureVideo technology late last year, one of the key features that both graphics card giants have been touting is their ability to accelerate the decoding of high definition video.  Microsoft’s Windows Media Video 9 codec is one of the main candidates for the HD DVD video standard and in fact you can already find a few movies on the shelf that use this codec for outstanding visual quality. 

NVIDIA told us that the new 7800 GTX had even better acceleration than the previous generation parts, mainly due to the increased pixel pipelines that the architecture sports.  These same shader units are used for programmable HD decoding as well as typical game acceleration. 

NVIDIA GeForce 7800 GTX GPU Review - Graphics Cards 87

Comparing the 7800 GTX to the 6800 Ultra and the ATI X850 XT PE shows that indeed as claimed, the NVIDIA GeForce 7800 GTX is the fastest card we have tested for HD decoding for the gaming user.  While the 7800 GTX had a 6.5% lower average CPU utilization than the ATI offering, even more noticeable is the 13% lower spikes of CPU utilization that it showed consistently. 

Overclocking the 7800 GTX

While it is often the case that engineering samples of hardware are not as high quality as the retail boards that will ship, and thus initial overclocking results may not be a useful point to look into, that is not the case with this 7800 GTX release.  Not only has NVIDIA had these cards working and running for quite some time, but they have also had the chance to tweak the chips and get the boards more than ready for the media and end users. 

Using the integrated Coolbits hack of the NVIDIA Detonator driver set, I went about overclocking the GPU core and memory clocks independently to find their highest points of stable usage.  Usually, when running two GPUs in SLI mode, the overclockability is slightly lower, but that was not the case in this instance.  For both a single and dual card setup I was able to overclock the default 430 MHz core and 1.2 GHz memory clock to 489 MHz core and 1.31 GHz memory clock.  That is a 13% core overclock and not to shabby for standard cooling and voltages, etc. 

NVIDIA GeForce 7800 GTX GPU Review - Graphics Cards 88

Our overclocking results on the 7800 GTX

I ran the overclocked setups through a multi-hour loop of 3DMark05 looking for artifacts as well as any potential crashing, and I came up empty handed, which is good.  Here are the results of the overclocked cards in a 3DMark05 run at 16×12 with 4xAA and 8xAF enabled:

NVIDIA GeForce 7800 GTX GPU Review - Graphics Cards 89

Very impressive scores, and a single card sees a healthy 11% gain from our 13% core increase. 

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