New memory interface/Ultrashadow

256-bit memory interface

If you recall the original GeForce FX 5800 Ultra, the card often outperformed ATI’s RADEON 9700 PRO when running without antialiasing and anisotropic filtering enabled. Once these features were turned on however, GeForce FX 5800 Ultra was often left eating ATI’s dust. This is partially because GeForce FX 5800 Ultra was giving up nearly 4GB/sec of memory bandwidth to the RADEON 9700 PRO. Once you turn on these visual quality features, the demands on the memory subsystem of the graphics card increases, especially as you crank up the screen resolution. The memory subsystem in GeForce FX 5800 Ultra literally became a bottleneck.

To address this, NVIDIA has doubled the width of the memory interface to 256 bits. This wider path to and from memory allows twice the amount of data to be transferred each clock cycle; resulting in greater performance than if a 128-bit interface had been used.

This 256-bit interface is paired to 425MHz DDR memory (850MHz effective), resulting in up to 27.2GB/sec of peak memory bandwidth. In comparison, ATI’s RADEON 9800 PRO offers 21.8GB/sec of memory bandwidth.

Did you notice that we said GeForce FX 5900 Ultra sports 425MHz DDR and not DDR2 memory? While GeForce FX 5900 Ultra’s memory controller supports both memory types, NVIDIA has decided to go back to traditional DDR memory in GeForce FX 5900 Ultra for cost reasons. As it’s still a brand new memory type, DDR2 memory is more expensive than DDR and isn’t widely available. And while it does offer reduced power consumption, we’ve also noticed that current DDR2 modules generate a lot of heat.

UltraShadow technology

Since its announcement, id Software’s Doom III has been one of the most hotly anticipated titles on the market. In addition to the game itself, its underlying game engine will be used in a number of upcoming titles for years to come. Quite frankly, the jaw-dropping graphics in this game are going to move lots of video cards as gamers will upgrade their current graphics card to experience all of the visuals of John Carmack’s latest creation.

NVIDIA and ATI realize this, so they’re both coming up with ways to enhance the performance of their products with this and other next generation titles. Advanced shadows and lighting will be one of the keys to drawing end users into these immersive environments, as witnessed in Tom Clancy’s Splinter Cell. NVIDIA’s UltraShadow technology has been developed to address this need.

NVIDIA's UltraShadow technology

With UltraShadow, shadows can be calculated more quickly by defining the areas that need to be calculated, allowing the graphics core to only render the area of the shadow that is necessary, increasing efficiency. (Much like the z-buffer is used to cull unnecessary pixels.) This is accomplished by the programmer, who must define the bounded portions of the scene, depicted as “depth bounds” in the image above. The graphics core limits all calculations of lighting effects to this area, allowing the shadow to be rendered more quickly and with greater efficiency -- the more complex the scene (for example a room with multiple light sources and objects), the more significant the performance improvement. Unfortunately, UltraShadow is only currently exposed through OpenGL, not Direct3D. NVIDIA plans to address this shortly however.