OverclockingThe overclocking results 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 which is why our results here can only serve as a guideline for what you can expect from your card.
Maximum overclock on our card is 1130 MHz GPU clock (11% overclocking) and 1640 MHz memory (9% overclock).
Overclocking looks good on paper, but these clock speeds will rarely be active. The card usually starts out at high clocks (when it's cool), but clocks drop down once it runs hotter and power consumption goes up, which our real-life OC results coming up confirm. The OC frequencies are also not anywhere near the 1200+ MHz that we see on single-GPU HD 7970 cards, or the ARES II, but they are promising enough, and I think LN2 overclockers might have fun with the HD 7990.
|Maximum Overclock Comparison|
|Max. GPU Clock||Max. Memory Clock|
|HD 7990||1130 MHz||1640 MHz|
|ASUS ARES II||1220 MHz||1810 MHz|
|ASUS HD 7970 Matrix||1230 MHz||1790 MHz|
|Sapphire HD 7970 Toxic||1275 MHz||1885 MHz|
|AMD HD 7970 GHz||1185 MHz||1635 MHz|
Important: Each GPU (including each GPU of the same make and model) will
overclock slightly differently based on random production variances. This table
just serves to provide a list of typical overclocks for similar cards, determined
during TPU review.
Overclocked PerformanceUsing these clock frequencies, we ran a quick test of Battlefield 3 to evaluate the gains from overclocking.
Actual 3D performance gained from overclocking is 4.1%.
Voltage TuningIt has been a long known fact that overclocking headroom increases as soon as you increase the operating voltage. Software voltage control on VGA cards has, until recently, been the exception, and most users were not willing to risk their warranty by performing a soldering voltmod. Almost all current graphics cards have voltage control to lower the power consumption by throttling voltage during idle and slight load.
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 through software, not actual measured voltage. The card was installed into a case with fan settings at default. Memory will not be overclocked. We will, with a card that has thermal throttling, reduce the operating frequency to keep performance as high as possible 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 too 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 card's overclocking potential over its base clock. Temperature is plotted in red using the °C scale on the right side of the graph. An additional graph shows full system power draw in orange, measured at the wall socket while running at the given voltage, clock, and temperature.
Once I started adjusting the voltage, PowerTune would immediately reduce GPU clock to 950 MHz, no matter what actual frequency was set. To overcome this, I set the Power Limit slider in CCC to its maximum. This allowed testing to continue and showed some frequency gains while quickly increasing power consumption and GPU temperature. At 1.35 V, the card reached a toasty 95°C with the default fan profile already running the fans at 100%. Any further voltage increase got applied to the circuitry, but had no effect on overclocking as some sort of safeguard became active. Whether that is due to the temperature of 95°C or some high-power draw condition, I cannot say, since I have no way of reducing GPU temperature to verify or debunk such theories.
Overall, voltage tuning only provided relatively slim clock gains. It is still nice to see voltage control available, unlike on NVIDIA cards, which could make this card attractive to extreme overclockers.