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Power Consumption, Temperature, Noise and Overclocking

At first we decided to find out how the electrical characteristics of Asus HD 6870 DirectCU differ from the reference Radeon HD 6870. To accomplish this we tested our today’s hero in our traditional testbed with the following configuration: 

  • Intel Core 2 Quad Q6600 CPU (3GHz, 1333 MHz FSB x 9, LGA775)
  • DFI LANParty UT ICFX3200-T2R/G mainboard (ATI CrossFire Xpress 3200 chipset)
  • PC2-1066 SDRAM (2x2 GB, 1066MHz)
  • Enermax Liberty ELT620AWT PSU (620W)
  • Microsoft Windows 7 Ultimate 7 64-bit
  • CyberLink PowerDVD 9 Ultra/"Serenity" BD (1080p VC-1, 20 Mbit)
  • Crysis Warhead
  • OCCT Perestroika 3.1.0

The new testbed for measuring electric characteristics of graphics cards uses a card designed by one of our engineers, Oleg Artamonov, and described in his article called PC Power Consumption: How Many Watts Do We Need?. As usual, we used the following benchmarks to load the graphics accelerators:

  • CyberLink PowerDVD 9: FullScreen, hardware acceleration enabled
  • Crysis Warhead: 1600x1200, FSAA 4x, DirectX 10/Enthusiast, "frost" map
  • OCCT Perestroika GPU: 1600x1200, FullScreen, Shader Complexity 8

Except for the maximum load simulation with OCCT, we measured power consumption in each mode for 60 seconds. We limited the run time of OCCT: GPU to 10 seconds to avoid overloading the graphics card's power circuitry. Here are the obtained results:

While the ordinary Radeon HD 6870 consumes 124 watts in 3D mode, the ASUS HD 6870 DirectCU needs 22 watts more, although its GPU frequency is only 15 MHz higher than the reference card’s. The explanation is simple: the reference card has a GPU voltage of 1.175 volts and the ASUS card, 1.2 volts. But we must confess we didn’t expect such a notable difference in power consumption due to such a small difference in voltage.

There is another interesting thing about the behavior of the ASUS card’s power subsystem. In the power-saving modes the second power connector has a higher load than the first one, but launching a 3D application changes the situation: it is the first connector that takes the bulk of the total load then, up to 7 amperes or over 80 watts.

Besides, those power-saving modes do not really save much power. The ASUS HD 6870 DirectCU is not as economical as the reference Radeon HD 6870. The GeForce GTX 580 needs only 30 watts for video playback (it drops its clock rates soon after beginning to play video content) whereas the EAH6870 DC consumes 50 to 70 watts then. So, the ASUS HD 6870 DirectCU would not be a good choice for an HTPC, but it is not really meant for such systems, either.

The cooling system should be given credit for copying with its job well and better than the reference card’s, notwithstanding the higher heat dissipation of the GPU with increased voltage. It keeps the GPU cooler by 8 degrees compared to the reference card in 3D applications, which is nice. Let's check out the noise factor now.

Well, the dimensions and overall quality of the cooler make it more comfortable in terms of noisiness than the reference Radeon HD 6870. The fan was rotating at 1430 RPM in 2D mode and accelerated to only 1600 RPM in 3D applications.

Interestingly, the ASUS HD 6870 DirectCU is much quieter than the ASUS ENGTX460 DirectCU TOP that we tested earlier. The latter’s cooler may have been defective or too aggressively set up in order to ensure maximum cooling performance at the expense of acoustic comfort. Overall, the HD 6870 DirectCU is far from noisy. The GeForce GTX 560 Ti is perhaps the only card that is quieter.

As for overclocking, our sample of the ASUS HD 6870 DirectCU refused to increase its GPU voltage above the factory setting of 1.2 volts using the ASUS SmartDoctor utility. We even updated the card’s BIOS but to no effect.

Well, even without any increase in GPU voltage we managed to overclock the graphics core to 1030 MHz and the memory chips to 1265 (5060) MHz. The card was stable at such settings, its GPU temperature rising up to 80°C, but that’s normal for today’s top-end graphics cards. So, we decided to focus our tests on the performance of the overclocked ASUS HD 6870 DirectCU because its factory overclocking (by 15 MHz for the GPU) cannot be greatly rewarding whereas our own overclocking will help us see what a Radeon HD 6870 needs to compete with a GeForce GTX 560 Ti.

 
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