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 930 MHz core (1% overclock) and 1235 MHz Memory (10% overclock). Seeing only 930 MHz on this card is very disappointing, but I'm sure that we were unlucky with our sample. At this time all cards, reference and overclocked, are built in the same factory during the same production run. On the other hand memory overclocked a bit better than the other HD 6870 card we tested so far, but again, this seems to be within the normal spread of overclocks between cards.

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 3.0%.

Temperatures

Low idle temperatures suggest that there may be some potential for less fan noise here. Under load the card is already at quite high temperatures, so it seems not much can be done here for 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.



Increases to voltage help the card with overclocking, but it is still not enough to pass the 1000 MHz barrier.

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.