Overclocking

To find the maximum overclock of our card we used a combination of GPUTool and our benchmarking suite.
The overclocks listed in this section were achieved with the default fan and voltage settings as defined in the VGA BIOS. Please note that every single sample overclocks differently, that's why our results here can only serve as a guideline for what you can expect from your card.



The overclocks of our card are 945 MHz core (20% overclock) and 1165 MHz Memory (17% overclock). Both overclocks are phenomenal and show that AMD has mastered the 40 nm production process. Such an overclocking potential enables willing users to buy the cheaper HD 6850 and overclock it to HD 6870 performance levels.

Overclocked Performance

Using these clock frequencies we ran a quick test of Call of Duty 4 to evaluate the gains from overclocking.


The actual 3D performance gained from overclocking is 16.2%.

Temperatures

Temperatures are low across the board, I would have preferred to see slightly higher temperatures in return for less fan noise.

Voltage Tuning

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It has been a long known fact that overclocking headroom increases as soon as you increase the operating voltage. Until recently, software voltage control on VGA cards has been the exception and most users were not willing to risk their warranty by performing a soldering voltmod. Nowadays almost all current graphics cards have voltage control in order to achieve low power consumption by lowering voltage when in idle or slightly loaded.
In this section we will increase the GPU operating voltage step by step and record the maximum clock speed possible. Voltage is listed as the value that the voltage regulator reports via software, not actual measured voltage. The card was installed in-case, with fan settings at the default, memory will not be overclocked either. If a card has thermal throttling we will reduce the operating frequency to keep performance at maximum for a given voltage. Please note that the fan profile will have an effect on observed temperatures: if the card gets hotter the fan will ramp up to reduce temperatures or keep them from rising fast.

The following graph shows the overclocking potential we saw on our sample. GPU clock is represented by the blue line, which uses the vertical clock scale on the left. The scale starts at the default clock to give a feel for the overclocking potential over the base clock. Temperature is plotted in red using the °C scale on the right side of the graph.



The card gains nicely with voltage increases, but once we set a voltage beyond 1.4V the voltage regulator circuitry would run too hot and the card would throttle down. In order to still reach maximum performance we had to reduce clock speed until the throttling stopped.

Clock Profiles

Modern graphics cards have several clock profiles that are selected to balance power draw and performance requirements.
The following table lists the clock settings for major performance scenarios and the GPU voltage that we measured. We measure on the pins of a coil or capacitor near the GPU voltage regulator.