GeForce 6800 GS: Where Two Generations Meet
Today’s graphics processors are often pin-compatible with their predecessors for the developers not to spend time and money on designing new PCBs. An example of this approach is the RADEON X8 series from ATI Technologies: the entire series, from X800 GT to X850 XT Platinum Edition, use unified PCBs with minor variations.
NVIDIA’s GeForce 7800 and GeForce 6800 GPUs are also physically compatible, so the company didn’t have to develop the PCB for the new product from scratch. They already had the GeForce 7800 GT printed circuit board. Simple (i.e. cheap) and rather compact, it could normally power up a 20-pipelined GPU working at 400MHz and memory clocked at 1GHz. So, it was sure to suffice for the 12-pipelined NV42, even clocked at a high frequency. As you have already guessed, that PCB became the foundation of the GeForce 6800 GS graphics card:
If it were not for the cooler and the connectors (DVI-I and D-Sub), you wouldn’t tell the new card from a GeForce 7800 GT. NVIDIA abandoned the efficient but noisy cooling system of the GeForce 7800 GT, but equipped the reference sample of the GeForce 6800 GS with the cooler from the GeForce 6800 GT. In brief, the cooler consists of three parts: a plastic casing with a blower, a GPU heatsink and an L-shaped heatsink with a heat pipe for cooling the memory chips.
The L-shaped heatsink on our card was electrochemically blackened for better heat transfer, while in the original cooler it had been just painted black. The pipe transfers heat to the heatsink section which is blown at by the fan. This way the GDDR3 memory clocked at 500 (1000) MHz is effectively cooled. For comparison, the memory chips on RADEON X800 GTO and RADEON X1600 XT cards is not cooled at all.
The GPU heatsink is made of copper, although NVIDIA had earlier used all-aluminum heatsinks of the same shape. It was ASUS Computer that first employed a copper heatsink on a GeForce 6800 in its unique V9999 Gamer Edition graphics card which actually had the same technical characteristics as the today’s GeForce 6800 GS, but worked on the AGP platform. Generally speaking, copper has better heat conductivity but worse heat capacity than aluminum. In other words, a copper heatsink takes heat off the GPU faster and more effectively, but requires a stronger airflow. The blower installed in the GeForce 6800 GS cooling system can create this airflow, but its noise characteristics may be too much for a sensitive ear – we’ll talk about that in the next section of the review. The main radiator is fastened to the PCB with four spring-loaded screws, so a proper contact with the GPU is guaranteed.
The fan speed control system lacks feedback, which we have on graphics cards from ATI Technologies, but it can work in three fixed-speed modes: 2D, Low Power 3D and Performance 3D. The speeds in these modes can be adjusted to some extent with the RivaTuner utility, so you can reduce the noise from the card a little in a particular mode.
Typical dark-gray thermal paste with low heat resistance is employed as a thermal interface between the heatsink’s sole and the GPU die. The memory chips touch the heatsink through cloth pads soaked in white thermal paste like on other NVIDIA products. The cooling system is overall satisfactory. It used to cope nicely with 0.13-micron 16-pipelined NV40/45 chips, so it should handle a 0.11-micron 12-pipelined NV42 as well.
We removed the memory heatsink to check the marking. NVIDIA employed popular K4J55323QF-GC20 chips of GDDR3 memory from Samsung here. They have 256Mb capacity, 2.0 voltage, and 2.0ns access time. It means they are rated to work at 500 (1000) MHz frequency.
And then we took off the main heatsink to see an ordinary NV42 chip that we described some long time ago in our MSI NX6800 review . As you remember, this GPU has 12 pixel and 5 vertex processors and can work at frequencies over 400MHz. The GPU frequency is declared to be 425MHz in the GeForce 6800 GS specification. This is 100MHz above the frequency of the GeForce 6800. Combined with 500 (1000) MHz memory frequency, it should ensure a tremendous performance gain – the GeForce 6800 GS seems to have much more raw power than the GeForce 6800.
The card is not equipped with a VIVO chip, although there is a place for it on the PCB. NVIDIA probably tried to reduce the cost of the product as much as possible, but some graphics card manufacturers will probably equip their versions of the GeForce 6800 GS with an appropriate chip from Philips.
The GeForce 6800 GS fully supports NVIDIA’s SLI technology. Unfortunately, we couldn’t test it in this mode since we had only one sample of the GeForce 6800 GS on our hands. But as soon as we get a second one, we’ll tell you how fast such SLI configurations may be.