VPU (cont’d)

In the case of playback of HD-DVD and Blu-Ray, the programmable VPU is used primarily for decoding the video such as MPEG-4 AVC (H.264) decoding. While the VPU across the GeForce 6 and 7 line is identical in design, performance is dependent on the core clockspeed. The advantage of this is that you won’t have to buy the top-of-the-line GPU to get H.264 decode acceleration. Likewise, as new features are developed for the GeForce 7, it’ll often trickle down into the older GeForce 6 models. Still, this also means that the VPU in the GeForce 7950GT at 550MHz is slower than the VPU in the GeForce 7600GT at 580MHz. Of course, this performance difference is purely theoretical.

The shaders definitely do not come into the picture for H.264 decoding. However, NVIDIA’s de-interlacing and noise-reduction algorithms are accelerated by the shader portion of the GPU to some degree. Although the current algorithms run fine on standard 7600GT, it is possible that NVIDIA will have new algorithms in the future that will benefit from the added shader performance of the 7950GT.

Fixed Function Pipeline

The GeForce 7 GPUs have a 4x5 tap video scaler for both upsampling and downsampling. This means that for each pixel, the GPU is analyzing a total of 20 pixels when scaling the image up. For comparison, the latest AVIVO Radeon’s are 6x10 tap, high-end Faroudja chips are 12x12 tap, and Silicon Optix’s Realta and ReonVX with HQV processing are 32x32-tap. The older GeForce FX and Intel GMA950 were 5x3, and pre-AVIVO ATI Radeon’s were 4x4. In general, the higher-tap filters have had better results however variations in the actual algorithm being used prevent direct comparison.

HDCP encoding is also a feature that is performed by a fixed function portion of the GPU. In order to have full HDCP support, the graphics board needs a secure CrytoROM with the HDCP passkeys on the chip. If you want to play HD-DVD or Blu-Ray content over a DVI or HDMI connection, you will need HDCP. If you want to play HD-DVD or Blu-Ray content over VGA or component video, you won’t need HDCP. However, in 2009 you will probably lose 75% of the resolution:

	DVI or HDMI (w/HDCP)	DVI or HDMI (no-HDCP)	VGA or Component Video
Home-made HD-DVD/BD (no AACS, no ICT)	Full Resolution	Full Resolution	Full Resolution
HD-DVD/BD made in 2006 (AACS; no ICT)	Full Resolution	No display	Full Resolution
HD-DVD/BD made in 2009 (AACS and ICT)	Full Resolution	No display	No display or 1/4th resolution