Let's go a bit more into detail:

We all know that the higher the clock frequencies of the video card are, the better your score will be. But sometimes the memory is limited by the gpu. Should the shader be linked to the gpu? What overclocks can I expect with what cooling?

Solving these questions is important if you want to get the most out of your card. The answers are different for every card as not every card overclocks the same. If you want to be thorough, the following figures are a must.

Overclock versus Voltage

During the weeks of the preparation of the final bench session, I had the chance to test the clock frequencies with stock air-cooling. I have graphs ready to show, but they are not useful as a lot depends of the temperature of the environment and the card itself. Though, I will give you a few pointers.

- The memory is very sensitive for higher voltages. Be careful when overclocking, because if you kill one memory chip, you're card is not useful anymore. Tests will show that raising the memory clock doesn't really help to get more FPS.
- The GPU can clock very high with relatively low voltages IF the temperature stays low. When testing in the attic (room temp around 15°C) I reached 850MHz GPU stable with 1,35v.
- Check where the limit of the shader clock lies. With my card this is 2150MHz, more Vgpu doesn't help.

GPU, shader and memory clocks

The frequency you set is not always the actual frequency! Most cards work with certain levels of frequencies. For instance, if you set 712MHz as GPU frequency, the actual frequency might be 718MHz. The same goes for shader and memory frequencies.



Notice how +100MHz set in Rivatuner equals exactly +100MHz real speed. It's very easy to calculate what speed you'll be working at now.



The shader clock can now be set unlinked, which means that you can overclock it separately. In theory both clocks are now working independent from each other; however, please know that the following rule always counts:

Shader clock >= 2 x Core clock



GPU, shader and memory performance scaling

Next up: how does increasing the frequencies translate into performance increase? We used 3DMark03's Nature test to calculate the performance and Rivatuner to overclock our card.



Gpu and shader clock are linked, as we can't overcome the rule we've stated above.. Two sets of data, one with the memory clocked at 1000MHz and one with the memory clocked at 1100MHz.

The GPU/Shader overclock is pretty important as it keeps increasing the performance. Higher clocked memory means that the GPU/Shader performance scaling will be a lot higher. As a matter of fact, the score scales almost linearly with the raise in clock frequencies!



Many people tend to hype the Shader clock as the most important of all three. In fact, this isn’t the whole truth. The shader clock is important, but in some cases it doesn't really matter whether the shader is increased or not. As you can see, in some cases, we only get 5FPS more when clocking the shaders 150MHz higher.

In our previous video card overclocking article with the 8600 GT, we saw less impact of the shader clock, but with the 9600GT, the shader seems to play a bigger role in the graphics card's power.

When overclocking the card on air we noticed that the shader clock maxed out at 2150MHz. Even higher voltages didn't help us to go higher.



Is it interesting to risk to kill your memory chips due to over voltage? No, not at all. At 1000Mhz, the card is almost as fast as at 1100MHz. Raising the voltage to get higher clocks is not recommended, however, raising the voltage is interesting for another reason, which we'll get to later on in this article