Gigabyte’s card is based upon NVIDIA’s NV43 chip, which is a derivative of the NV4x architecture announced last year. The 6600GT has 8 pixel pipelines, the same as the high-end from the year before. With a clock speed of 500MHz, the 6600GT has a fill rate of 4 Gigapixels a second and 4 Gigatexels a second. The 6600GT has 3 Vertex Shader pipelines with 1.5 vertices outputted per clock.

NVIDIA has been at the forefront of evangelizing Shader Model 3.0. Microsoft first introduced programmable shaders in the DirectX 8.0 API back in 2001 with the release of the Xbox and GEFORCE3 from NVIDIA. 2002 saw the release of DirectX 9.0 with two shader models 2.0 and 3.0. The key ingredients of SM 2.0 are Pixel Shader 2.0 and Vertex Shader 2.0.

Key features of Pixel Shader 3.0 include nearly unlimited shader lengths (65,536 limitation by DirectX 9.0c), looping a branching of Pixel Shader programs, a back-face register, vertex texturing and more. The NV4x architecture was the first to fully support Microsoft’s PS 3.0 specification recently joined by ATI’s R1K family of cards. NVIDIA has the advantage of having their SM 3.0 hardware out first so developers were using their hardware to work on games needing the advanced pixel shaders.

Vertex Shader 3.0 key features include: nearly unlimited shader lengths (65,536 versus 256 for SM 2.0), dynamic looping and branching support, geometry instancing, and vertex texturing. Geometry instancing allows the developer to take one model and use vertex streams to modify that object. For example a forest of trees can have variation in height, in leaves etc.. With Instancing you can vary the attributes of the trees in a forest without rendering each tree separately.

SLI stands for Scan Line Interleave err, that was 3DFX’s definition. NVIDIA calls SLI Scalable Link Interface. To enable SLI you need an SLI-ready motherboard like an ASUS P5N32-SLI board, two NVIDIA based video cards that are the same model, and the drivers. SLI modes include: AFR or Alternate Frame Rendering. In AFR, each card renders a frame one after the other. The second mode of SLI is called SFR or Single Frame Rendering. SFR has both cards working together to render a scene.

The human eye can distinguish color contrasts of a range of millions to one. A computer monitor, on the other hand, has limited contrasting capabilities. Video cards prior to floating point color precision had a limitation of 255:1 contrast ratio. With the advent of cards with FP color precision a range of 65,536 contrast ratio is possible. Valve has released a new demo based upon HL2, the Lost Coast demo. In this demo you can easily see the difference between HDR on/off and Blooming. If you’ve ever walked into bright sunlight after being in a cave or dimly lit area, the glare that blinds you momentarily is the Blooming effect. Valve implemented both the Blooming effect and HDR in HL2 Lost Coast. Here are three screenshots, one showing no HDR, one the Blooming effect and the other full HDR.