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Curbing Your GPU's Power Use: Is It Worthwhile?

AMD’s Radeon HD 6970

AMD’s Radeon HD 6970

AMD's Radeon HD 6970 is an altogether different beast compared to the company's Radeon HD 5870. We were pleasantly surprised to see that idle frequencies stay the same, regardless of any manual modifications to the core and memory clocks. The presence of a secondary BIOS on the card also means we have another safety net to recover from a bad flash, rather than ending up with a non-functional card.

No matter how hard we tried, the modified BIOS kept crashing the card

Unfortunately, the card we have (Asus’ EAH6970/2DIS/2GD5) refused to work with any modified BIOS settings. Disappointed, we limited ourselves to just changing core and memory clocks. After all, we only modified the 5870’s BIOS to work around its odd clock behavior. To change the card's operating voltage, we used Asus’ SmartDoctor utility.

Asus’ SmartDoctor let us to bypass the BIOS and change the GPU operating voltage directly, though it's limited to changing operating voltage in 3D mode. We noticed that after tweaking voltages, those changes are not reflected in other utilities, such as GPU-Z or AMD Overdrive. They simply report the voltage value written in the BIOS.

We settled on several settings for testing. In addition to default clocks (890/1375 MHz) and UVD clocks (500/1375 MHz), we played with lower memory clocks (890/1030 MHz and 500/1030 MHz). Together with voltage adjustments, we came up with a total of seven settings to test.

Core and Memory ClockChip Voltage
890/1375 MHz (full clock default settings)1.175 V
890/1375 MHz1.1 V
890/1030 MHz1.175 V
500/1375 MHz (UVD default settings)1.0 V
500/1375 MHz0.98 V
500/1030 MHz1.175 V
500/1030 MHz0.86 V

These settings should give us a more complete view of the effects of changing clocks and voltages. Again, keep in mind that variations between cards do exist. There is no guarantee that the settings we've chosen here will work with your card. As is usual with overclocking projects, your mileage will vary.

In order to verify stability, we ran through Crysis, PowerDirector, and Medal of Honor. Crysis quickly turns up rendering errors and triggers driver crashes if your settings are too aggressive. H.264-based encoding with PowerDirector really pushes the card with a sustained load, which works well for catching errors that didn’t crop up in Crysis. Finally, Medal of Honor turns out to be even more demanding from a power consumption viewpoint than Crysis or PowerDirector. Since we were not able to modify the card’s BIOS to change its clock and voltage settings for UVD mode, we skipped H.264 playback and idle power measurements testing.