Core details

The NV40 core powering NVIDIA’s GeForce 6800 enjoys an impressive feature set. Rather than adapt previous GeForce FX architectures, NVIDIA has employed an entirely new design for the 6800 family.

It all starts with the graphics core’s 16 pixel pipelines, twice that of previous graphics architectures. When combined with the GeForce 6800’s six vertex engines, the graphics core’s pixel processing power is significantly increased as is fill-rate. Basically, this allows the GeForce 6800 to pump a lot of triangles.

NVIDIA clocks the GeForce 6800 graphics core at 325MHz, which may sound like a low figure at first, but when you factor in the core’s 12 pipelines, the GeForce 6800 packs a respectable fill rate of 3.9 Gigatexels/second and a peak pixel fill rate double that of GeForce FX 5950 Ultra.

Paired alongside the GeForce 6800 core is 128MB of DD1 memory clocked at 350MHz (700MHz effective). Like previous GeForce FX 5900 series graphics cards, the 6800 features a 256-bit wide memory interface, which is responsible for keeping the NV40 graphics core fed with up to 22.4GB/sec worth of data. It’s this figure that could be the 6800’s greatest weakness; the memory subsystem of ATI’s RADEON 9800 XT provided its core with 23.4GB/sec of peak memory bandwidth, while the 5950 Ultra tops out at an impressive 30.4GB/sec. This could potentially put the GeForce 6800 at a disadvantage in situations where you’re memory bandwidth-bound. Such cases would occur at high screen resolutions and/or anti-aliasing and anisotropic filtering cranked up.

Board manufacturers can also outfit their GeForce 6800 board with 256MB of DDR1 memory.

If you need a little more performance, NVIDIA also offers the GeForce 6800 GT and GeForce 6800 Ultra. Both cards feature 16 pixel pipelines instead of the 6800’s 12, while the core and memory clock frequencies have been bumped up significantly as well: 400MHz core/550MHz memory on the GeForce 6800 Ultra, and 350MHz core/500MHz memory on the 6800 GT, both ship with 256MB of GDDR3 memory.

Shader Model 3.0

Of course, another key highlight NVIDIA has incorporated into GeForce 6800 is support for shader model 3.0. Shader model 3.0 builds on the specs of shader model 2.0, supporting more instructions and dynamic flow control (looping/branching). FP32 is also the minimum precision in shader model 3.0, versus FP24 in previous shader models.

Finally, support for features such as high dynamic range lighting are provided as is vertex processing with textures and centroid sampling. We provided a more detailed look at the new additions in shader model 3.0 as well as NVIDIA’s new graphics core in our GeForce 6800 Ultra Performance Preview. Please refer back to it for more details.