How to overclock the Radeon HD 6850 and HD 6870

Do the Barts, man…

Based on the successful Cypress GPU, the HD 6850 and HD 6870 aren’t direct replacements for AMD’s top-end HD 5870 and HD 5850 cards, despite the fact those have now been discontinued. Instead the HD 6870 is a designed as a cross between the HD 5850 and, frankly irrelevant, HD 5830, with the 6850 featuring an even more cut-down core.

But with GPU overclocking being on the Abbi Titmuss side of easy why don’t we see if we can put some bounce back into their stride?

The apps of choice
With the help of MSI’s Afterburner, the Furmark GPU stress-tester and Unigine’s Heaven 2.1 benchmark you can increase the clocks on pretty much any GPU out there.

But even though it is easy and safer than ever, we have to say there is always a risk pushing your card beyond the clockspeed it is rated at, and any overclocking can invalidate your warranty too. So, you’ve been warned.

Each manufacturer does have its own software, and if you want to get down and dirty with the voltage tweaking then using the OC suite created by your card’s maker is generally your only option. Their application will give you full access to the voltage tweaking elements of your card.

But if not you can still do all the memory, core clock and shader you need using MSI’s Afterburner. Voltage tweaking is probably the easiest way to shorten the life of a GPU, so be wary.

MSI’s Afterburner is a solid bet for GPU overclocking. The detachable hardware monitor allows you to keep tabs on the temperature.

In terms of tweaking software, we use Unigine’s Heaven 2.1, but if you can’t be dealing with its long loading time we’d suggest using FurMark. You can leave this application running on your Windows desktop as you tweak, helping you look out for artefacts as you go.

Keep on, keep on clocking
The process for overclocking graphics cards hasn’t changed much recently, which requires stepping up the memory frequency by increments of 5 to 10MHz, applying the settings, then check the FurMark window for signs of artefacting for at least a couple of minutes. If everything appears satisfactory then step it up another notch.

Keep doing this until signs of artefacting appears. Once you hit the limit, step it back a notch and hit Heaven 2.1 Benchmark for a serious stress-test.

Move over to the core/shader clock slider and start again, remembering to reset the memory slider to its default position.

Essentially, it’s the same drill as with the memory clock. Once the core limit is found, bring up the memory clock to the previous stable overclock and stress test with both clocks.

The overclocking results
We managed to boost the clockspeeds on both cards, but in each case we had to push the fan speed too by 50 to 60 per cent. But the AMD stock cooler isn’t the quietest at high speeds. Heaven 2.1 was tested at 2,560 x 1,600 and the rest of the benchmarks are at 1,680 x 1,050.

Taking the HD 6850 first, the news isn’t great on the overclocking front. From the original 775MHz core clock and 1,000MHz memory clock we could only boost that to 840MHz and 1,080MHz respectively.

The memory clock was especially resistant to change, but the 65MHz jump on the core clock should do good things. Unfortunately the whole overclock only managed an extra 4fps and we had to push the fan speed up to a wind turbine-esque 60 per cent.

The overclock may smooth your gaming out slightly but the noise will be more noticeable than the extra frames.

The news is a bit better for the pricier HD 6870, but not by much. The new AMD card comes with a core clock of 900MHz and a memory clock of 1,050MHz; We managed to push that to 970MHz and 1,170MHz respectively.

On the whole that still doesn’t add up to a hell of a lot extra performance in games, bizarrely apart from Far Cry 2. The jump in clockspeeds gave a huge boost, especially at the 1,680 x 1,050 resolution. Here we saw the HD 6870 garner an extra 16fps, which will really make a noticeable difference in-game.

In DiRT 2 and Just Cause 2 however the boost was much less tangible, giving us almost as few extra frames per second as the HD 6850 produced.

So, as well as being limited in vanilla flavour the new, DirectX 11 cards from AMD are also quite poor overclockers too. That shouldn’t be surprising however as the Barts core is a slightly refined version of the Cypress GPU found in the HD 5870 and HD 5850 and so is already performing at near its peak.

Posted on Friday, December 10th, 2010 at 10:31 am under Articles. You can subscribe to comments. You can leave a comment, or trackback from your own site.

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