HIS Radeon HD 6990 Crossfire review

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Overclocking The R6990


Overclocking the R6990

As most of you know, with most videocards you can apply a simple series of tricks to boost the overall performance a little. You can do this at two levels, namely tweaking by enabling registry or BIOS hacks, or very simply to tamper with Image Quality. And then there is overclocking, which will give you the best possible results by far.

What do we need?One of the best tools for overclocking NVIDIA and ATI videocards is our own AfterBurner which will work with 90% of the graphics cards out there. We can really recommend it, download here.

Where should we go?
Overclocking: By increasing the frequency of the videocard's memory and GPU, we can make the videocard increase its calculation clock cycles per second. It sounds hard, but it really can be done in less than a few minutes. I always tend to recommend to novice users and beginners, to not increase the frequency any higher than 5% on the core and memory clock. Example: If your card runs at 600 MHz (which is pretty common these days) then I suggest that you don't increase the frequency any higher than 30 to 50 MHz.

More advanced users push the frequency often way higher. Usually when your 3D graphics start to show artifacts such as white dots ("snow"), you should back down 10-15 MHz and leave it at that. Usually when you are overclocking too hard, it'll start to show artifacts, empty polygons or it will even freeze. Carefully find that limit and then back down at least 20 MHz from the moment you notice an artifact. Look carefully and observe well. I really wouldn't know why you need to overclock today's tested card anyway, but we'll still show it.

All in all... do it at your own risk.

Original This sample Overclocked
Core Clock: 830MHz Core Clock: 880MHz Core Clock: 955MHz
Shader Clock: 830MHz Shader Clock:880MHz Shader Clock: 955MHz
Memory Clock: 5000MHz Memory Clock:5000MHz Memory Clock: 5600 MHz

Now we had a bit of an issue with 3rd party overclocking, so we opted to use the internal OverDrive function in the AMD drivers. AMD gives a lot of tweakability in terms of MHz versus sliders.

AMD Radeon HD 6990

We are not overclocking the CrossfireX configuration by the way. I was seriously concerned about the PSU load.

Now there is a little room left for overclocking, but you need to wonder ... why you should do it. The card already runs pretty hot and noisy -- the performance however is already beastly. You can imagine that overclocking won't help you out a lot at this perf level.

Regardless of that, with Overdrive make sure you do the following:

  1. Enable AMD Overdrive
  2. Increase power control settings to +20%
  3. Adjust FAN RPM as required
  4. Find your preferable overclock
  5. MAKE SURE you do the above with each of the two GPUs. See the blue colored pull down in the screenshot, you need to apply the settings for each GPU.

We left the fan RPM control at default in all circumstances. We reached a very decent overclock showing a decent increase in overall performance. Voltage tweaking is not yet option. Our stable end result was 955 MHz on the core and 5600 MHz on the memory. Here as well the temps did not change very much, DBa levels remain roughly similar but noisy. For overclocking, as stated, we set PowerTune to it's maximum +20 value. 

Above we have Battlefield Bad Company 2, maxed out image quality settings as before with 8xAA 16xAF

Above we have Metro, maxed out image quality settings as before with AAA mode and 16xAF.

Above we can see 3DMark 11 - the Performance mode is applied here. Alright, enough benchmarks we say, let's head onwards to the conclusion.

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