We’ve had a fair amount of time to play with the Radeon HD 5850 now, and let us begin by saying that this card packs a serious punch. Even at its factory defaults, the 5850 offers significant performance, but it’s capable of so much more. To that end, follow along as we show you how to squeeze up to 25% additional performance out of your HD 5850.

As with all jobs, we need to begin by gathering the correct tools. While we can make a certain amount of progress with the Overdrive feature of the Catalyst Control Center, the imposed limits are nowhere near what the card is actually capable of achieving. To get around this problem, we’re going to need some extra programs.

Utilities

• AMD GPU Clock Tool: The AMD-approved overclocking utility which bypasses BIOS limitations.
• MSI Afterburner: Needed to control the card’s fan speed.
• Furmark: Stress-testing application for your overclock.
• Unigine Heaven: DirectX 11 Benchmarking tool.

Test setup

Memory overclocking

The first thing you’ll want to do is determine the quality of the RAM on your 5850. This can be a slightly tedious process, but it is worth doing this first, because the 5850’s core clocks do not affect RAM stability. Therefore, whatever maximum stable setting your RAM achieves can be used later while experimenting with core clocks.

To begin, fire up Furmark and begin a stability test in a 1024×768 window; it doesn’t matter if other applications are placed on top, but make sure that it is not minimized. Give Furmark a couple of minutes to get the card warmed up, and then open the AMD GPU Clock Tool. The stock VRAM speed on the 5850 is 1000MHz, and that is the setting you should see to begin with.

Most 5850s are capable of exceeding the overdrive limit set in the Catalyst drivers, so we suggest setting your memory clock to 1150MHz as your starting point. After you apply the setting, bring the Furmark window to the foreground, and allow the test to run uninterrupted for about 15 minutes. If at the end of 15 minutes the PC has not rebooted and the graphics driver has not thrown a VPU recovery, begin a process of gradually increasing the memory clock by 5-10MHz and testing after every increase.

If the driver undergoes a VPU recovery or the PC restarts, you have discovered the point at which the memory on your graphics card is unstable. Reduce the memory clock by 10MHz, and allow Furmark to test the setting for at least three hours. We recommend this test be run for at least six hours if you believe you have determined your final memory clock.

If the test fails after an extended period of time, reduce the memory clock by another 10MHz and re-run the stability test. At this point, your memory clock should be stable. Our Gigabyte HD 5850 demonstrated a maximum stable memory setting of 1175MHz.

Testing the VRAM overclock with Furmark.

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