How to Overclock an ATI Radeon Graphics Card

The first thing to do when overclocking a graphics card is to gauge the current performance of your card. You can do this by FRAPSing a section of a game or running a synthetic test, but you need to see what effects (if any) your overclocking is having on your PC’s performance.

If you chose the real-world test remember that you’ll want a test that’s not limited by the speed of your CPU, that’s consistent from one run to the next and that’s repeatable. You’ll therefore need a game that’s graphically demanding, and to find a section of that game that doesn’t differ from one play-through to the next. This can be tricky, so a synthetic test might be better.


Synthetic tests have the benefit of being absolutely consistent from one run to the next, and they require very little setup time. A real-world test can require hours of double-checking numbers, finding and eliminating inconsistencies and general frustration. However, synthetic tests are just that, and while a 3DMark score of 14,000 rather than 12,000 might sound great, it doesn’t tell you whether your PC can now play Crysis and Very High detail.

Make your own decision on which method to use, based on what you want to achieve. For example, if you’re trying to get Bad Company 2 to play smoothly, it’s probably best to try to develop your own real-world benchmark for this game. Good examples of synthetic tests are 3DMark Vantage and Unigine Heaven, while many games have built-in benchmarks to give a semi-real-world test.

Get Overclocking!

Once you have your baseline performance, you’ll need an application to overclock your GPU. Most ATI partners have their own custom applications, but most applications work with most cards, so you could as easily use Zotac’s Firestorm, MSI’s Afterburner or another favourite. You could also use the OVerDrive section of the Catalyst Control Center, but this won't allow you to add extra voltage to your GPU.

Gigabyte has its own OC Guru tool which has all kinds of weird and wonderful features such as telling you how much power you’ve saved if you run your card in Eco mode. However, it’s the overclocking aspect that we’ll focus on here. Click the Profile 1 tab and you’ll see a set of sliders drop out of the lower edge of the window. GPU-Z is an excellent way to determine whether your overclocking application has actually overclocked your card, as you can also see below.


Your overclocking application will present three crucial sliders - Core, Memory and Voltage – plus manual fan control. Some applications have more options, but these are the important ones for overclocking. As ATI uses a single clock speed for an entire Radeon GPU (unlike Nvidia and its split clock speeds), the Core slider affects the frequency of the entire GPU. The Voltage slider is an interesting slider that’s usually only available for Radeon cards – it allows you overvolt your GPU, which should allow you to overclock it further. However, adding extra voltage will also increase the amount of waste heat a GPU creates and so could make your card louder, or if you’re unlucky overheat and crash.

We found that even with the Voltage of our card increased to the maximum that the OC Guru would give us, the card was perfectly stable. This voltage allowed us to increase the GPU speed to 975MHz. We found that this was the limit of the card by steadily increasing the GPU’s frequency in increments of 10MHz from the 950MHz stock frequency of our card – this is still a huge increase from the standard 850MHz clock speed of HD 5870 GPU.

After we applied each overclock, we ran our benchmark test a few times to see whether the card would overheat at its new speed and whether the overclock added any extra performance. By reading our overclocking efforts in our reviews, you should be able to take a short-cut and start overclocking near to the limit of your card, or the final overclock that you wish to achieve.

We next increased the memory speed of the card, again by sliding the bar upward in 10MHz increments. We settled on a final speed of 1,300MHz. This is the actual frequency of the memory, so after the quad-pumping ability of the GDDR5 the effective speed of our memory was 5.2GHz.


As you can see from the graph, our overclock was enough to make Crysis playable, something that even Nvidia's mighty (if loud, hot and power-hungry) GeForce GTX 480 couldn't manage. The overclock added 7-9fps of extra performance, which isn't bad for an hour or so of patience.

Overclocking Cheat List

Can’t be bothered to read all those words? Allow us to be of service:

• Determine your current performance Run a test to determine how fast your PC is before overclocking.
  
• Get a benchmark Whether synthetic or real-world, get a benchmark that allows you to stress your overclock and give you an idea of how much speed you’re adding. You can use FRAPS and play a section of a game, use an in-game benchmark or download a synthetic test such as 3DMark Vantage or Unigine Heaven.
  
• Get your overclocking toolkit Download an overclocking application and GPU-Z to verify that it’s working.
  
• Raise the frequencies gradually, testing as you go You should be able to add something like 100MHz to the Core frequency of a good card, and 100-200MHz to the memory speed. Remember that after applying every overclock you need to run your chosen benchmark a few times to check that it’s stable, and that it’s actually increasing the performance of your PC.
  
• Bragging Once you’re done, and you’ve added 20 per cent more speed for free, you can officially boast your l33t skills to your friends and family. But don’t go on about it too much, or you’ll become Tech Support Guy/Girl for the rest of your life.