OverclockingThe 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.
Maximum stable clocks of our card are 1075 MHz core (22% overclock) and 1775 MHz Memory (42% overclock).
PowerColor's HD 7950 PCS+ shows just as impressive overclocking potential as the AMD reference design boards. This is evidence that PowerColor did a great job with their PCB design and didn't cripple OC capabilities.
Overclocked PerformanceUsing these clock frequencies we ran a quick test of Call of Duty 4 to evaluate the gains from overclocking.
Actual 3D performance gained from overclocking is 18.9%.
Temperatures are great and even lower than on the HD 7950 with the AMD cooler, even though the card runs higher clock speeds and a lot quieter.
Voltage TuningIt 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 default, memory will not be overclocked either. If a card has thermal throttling we will 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 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. An additional graph shows full system power draw in orange, measured at the wall socket when running at the given voltage, clock & temperature.
Gains from voltage are not that big. At around 1.25 V we reach a maximum clock speed of 1160 MHz. Any further voltage increases yield lower maximum clock. Beyond 1.35 V the card will randomly shut off itself like the AMD reference design, probably due to OCP being triggered.
Clock ProfilesModern graphics cards have several clock profiles that are selected to balance power draw and performance requirements.
The following table lists the clock settings for important performance scenarios and the GPU voltage that we measured. We measure on the pins of a coil or capacitor near the GPU voltage regulator.
|GPU Voltage |
|Desktop||300 MHz||150 MHz||0.85 V|
|Multi-Monitor||350 MHz||1250 MHz||0.95 V|
|Blu-ray Playback||501 MHz||1250 MHz||0.95 V|
|3D Load||880 MHz||1250 MHz||1.09 V|
|CCC Overdrive Limits|