A little more than 14 months ago, NVIDIA released the GeForce 6800 Ultra, which was up until now this company’s most powerful graphic chip. 14 months without any innovation in high end products is very long time indeed even if we keep in mind that production issues and the change to PCI Express delayed the availability of this processor, and that SLI opens the door to higher performances with supported applications.
Now NVIDIA releases the GeForce 7800 GTX, previously known as the G70, the first GPU of the GeForce 7 line.
The GeForce 7800 in short
Because of the excellent performance of the GeForce 6 architecture, there was no necessity to start all over again like with the change from the GeForce FX to GeForce 6. The GeForce 7800 GTX architecture is more an evolution of the GeForce 6 rather than a revolution.
The first modification is in chip size. The number of transistors changes from 222 million with a 130 nm fabrication process for the NV40 to 302 million with a 110 nm fabrication process for the G70. TSMC is still in charge of production and despite the smaller fabrication process, the chip is slightly bigger and more expensive to produce.
The main innovation isn’t in frequency increase. It only goes from 425 to 430 MHz for the GPU and 550 to 660 MHz for the GGR memory restricted to 256 MB for the moment. Despite the increase in the number of transistors, NVIDIA claims 110 Watts power consumption comparable to the previous generation.
Let’s now move on to the real improvements of this chip. First off in terms of geometry, the number of vertex shading pipelines is increased from 6 to 8 (+33%). The most important progression, however, is in pixel shader processing power going from 16 to 24 pipelines (+50%). In addition, these pipelines have been modified to have a higher IPC (instructions per clock) for some uses (see pages to come for more details).
The number of ROP Engines (ROP means Raster Operation) remains unchanged. This is logical, because memory bandwidth isn’t significantly improved, and they write directly in this bandwidth. We remind you that they are also responsible for anti-aliasing, blending, Z-Buffer compression and double Z (the possibility to calculate twice as much Z data than full color + Z data with the GeForce FX/6/7).
In terms of functionalities, the GeForce 7800 GTX is a Shader Model 3.0 GPU like the GeForce 6. This shader model is not yet supported by ATI and will only be available with the next chip. Like the GeForce 6, it provides almost complete support of FP16 floating point textures. Therefore, it includes a floating point buffer, but is also capable of carrying out, unlike ATI’s current architectures, operations such as blending or filtering. It helps support HDR with more flexibility and efficiency. Only multi-sampling anti-aliasing isn’t supported with the FP16 format.
The main innovation in terms of functionality is, in fact, transparency anti-aliasing, which is supposed to provide an efficient anti-aliasing for transparent textures at a lower cost than the full-scene supersampling anti-aliasing. Also, the PureVideo engine, which was bugged with the NV40 and didn’t allow WMV9 HD video decompression acceleration, is now fully functional.
Finally, you should know that this GPU is natively PCI Express. For now, NVIDIA has not mentioned a possible AGP graphic card with an AGP <-> PCI-E HSI bridge.
