NVIDIA and ATI have become more and more interested in PCI Express for a few months now, because of end of the year sales and partnerships with OEMs. For the moment, however, the number of PCI Express is still limited. The lack of PCI Express Athlon 64 platforms and graphic cards has slowed down the development of this market. Aware of this issue and the difficult position of the GeForce FX in relation to the best selling Radeon 9800 Pro, NIVIDIA had to release a GeForce 6 6600 GT version compatible with the “good old” AGP slot!
The GeForce6 6600 GT
In a few words, the GeForce 6600 GT (already studied in this article) is to some extent half a GeForce 6800 GT. The number of pixel pipelines and vertex engines are reduced from 16 to 8 and 6 to 3, respectively. The bus memory was also changed to 128 bits.from 256 bits.
The GeForce 6 6600 GT includes all of the GeForce 6 architecture’s functions. Included are the Shader Model 3.0, which creates longer shaders and introduces dynamic branching, and full compatibility with FP16 format. So the 6600 GT is capable of HDR type lighting with more flexibility and efficiency. Finally, the 6600 GT integrates the PureVideo engine, which, in theory, is able to accelerate MPEG1/2/4 encoding. This function, however, isn’t yet available six months after its release.
What can the GeForce 6600 GT do in its AGP version? The first thing to notice is that this chip is located between the GPU and AGP slot, and is in charge of translating the AGP signal into PCI Express and vice versa. So with this chip NVIDIA is able to use the GeForce 6600 GT (which is inborn PCI Express) for AGP cards, and also the opposite as is the case with the GeForce FX.
Frequencies slightly vary between the AGP and PCI Express versions:
- GeForce 6600 GT PCI Express: GPU 500 MHz, GDDR3 500 MHz
- GeForce 6600 GT AGP: GPU 500 MHz, GDDR3 450 MHz
For the time being NVIDIA uses 2 ns memory with the AGP reference card. We believe this was a choice to reduce the fabrication costs due to HSI integration on the AGP version. We also noticed that unlike the PCI-E, the 6600GT AGP requires an additional power supply connector. The AGP only provides 40 watts to the cards compared to 75 watts for the PCI Express.
