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Overclockability

We know that AMD Radeon HD 7970s have very high overclocking potential. Moreover, their performance increases proportionally to their GPU frequency. Is the junior Tahiti Pro good in this respect, too? Frankly speaking, we were annoyed at being able to increase the clock rate of our Sapphire Radeon HD 7950 OC to no higher than 940 MHz at first attempt:

Well, that’s not so bad, actually. The frequency is 17.5% higher than that of the reference AMD Radeon HD 7950 and the temperature doesn't grow much:

But of course we had expected something better, especially as the card features such an efficient cooler.

Therefore we increased the GPU voltage from its default 0.993 to 1.2 volts and continued our overclocking experiment. At a GPU clock rate of 1150 MHz the Sapphire card could pass through most of our tests but showed some visual artifacts in certain games (Aliens vs. Predator (2010) and Metro 2033). So we had to roll back to 1100 MHz, which was far better than the original 940 MHz at the default voltage. Then we started to lower the voltage, finding the balance between frequency, voltage and stability at 1.15 volts and 1100 MHz (+37.5%).

The memory chips could be overclocked easily to 7360 MHz (+47.2%).

The GPU temperature of the overclocked card was 74°C under peak load, the fan speed being fixed at 75% or 3000 RPM.

At a lower speed of the fans the cooler couldn’t cope with the overclocked card, provoking visual artifacts and instability in games and benchmarks. Anyway, our sample of the Sapphire Radeon HD 7950 OC card proved to have very high overclocking potential.

Power Consumption

We measured the power consumption of computer systems with different graphics cards using a multifunctional panel Zalman ZM-MFC3 which can report how much power a computer (the monitor not included) draws from a wall socket. There were two test modes: 2D (editing documents in Microsoft Word and web surfing) and 3D (the benchmark from Metro 2033: The Last Refuge at 1920x1080 with maximum settings). Here are the results:

The systems with different graphics cards are close in power consumption in 2D mode, the overclocked six-core CPU being the more important factor. But when it comes to 3D applications, the GeForce GTX 580 system needs about 56 watts more than the Radeon HD 7950 configuration. The latter also needs 62 watts less than the Radeon HD 7970 system.

Interestingly, the HD 7950 needs 35 watts less even when clocked at the same frequencies as the HD 7970. Well, this difference can hardly be noticed in your electricity bill anyway.

 
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