Power Consumption

Cooling modern video cards is becoming more and more difficult, especially with users asking for quiet cooling solutions, which is why engineers are now paying much more attention to the power consumption of new video-card designs. An optimized fan-profile is also one of the few things that board vendors can do to impress with reference designs where they are prohibited from making changes to the thermal solution or components on the card.

For this test, we measured the power consumption of the graphics card only via the PCI-Express power connector(s) and PCI-Express bus slot. A Keithley Integra 2700 digital multimeter with 6.5-digit resolution was used for all measurements. Again, the values here only reflect the power consumption of the card measured at DC VGA card inputs, not of the whole system.

We chose Crysis 2 as a standard test representing typical 3D gaming usage because it offers the following: very high power draw; high repeatability; is a current game that is supported on all cards because of its DirectX 9 roots; drivers are actively tested and optimized for it; supports all multi-GPU configurations; test runs in a relatively short time and renders a non-static scene with variable complexity.

Power consumption results of other cards on this page are measurements of the respective reference design.

Our results were based on the following tests:

• Idle: Windows 7 Aero sitting at the desktop (1280x1024, 32-bit) with all windows closed and drivers installed. Card left to warm up in idle mode until power draw was stable.
• Multi-monitor: Two monitors connected to the tested card, both using different display timings. Windows 7 Aero sitting at the desktop (1280x1024 32-bit) with all windows closed and drivers installed. Card left to warm up in idle mode until power draw was stable.
• Blu-ray Playback: Power DVD 9 Ultra was used at a resolution of 1920x1200 to play back the Batman: The Dark Knight disc with GPU acceleration turned on. Playback started around timecode 1:19, which has the highest data rates on the BD with up to 40 Mb/s. Playback was left running until power draw converged to a stable value.
• Average: Crysis 2 at 1920x1200, Extreme profile, representing a typical gaming power draw. Average of all readings (12 per second) while the benchmark was rendering (no title/loading screen).
• Peak: Crysis 2 at 1920x1200, Extreme profile, representing a typical gaming power draw. Highest single reading during the test.
• Maximum: Furmark Stability Test at 1280x1024, 0xAA. This results in a very high no-game power-consumption that can typically be reached only with stress-testing applications. The Card was left running the stress test until power draw converged to a stable value.

AMD's biggest enemy in pulling off a successful HD 7990 design is power consumption. If power consumption is high, the card will run hot, be noisy and potentially slower to stay within certain power limits. That's why they have sorted their best Tahiti GPUs with the lowest leakage currents for use with the HD 7990. GPU-Z can read this value (as ASIC quality) and confirms that this card uses very low leakage chips (59.1% and 57.7%; 80%+ would be typical).
AMD's recent cards also include ZeroCore Power. It shuts the unused GPUs in a CrossFire configuration down and only wakes them up during gaming sessions (indicated by a green LED on the card).
Even with all those improvements, the HD 7990 is not nearly as power efficient as the competition from NVIDIA.

When looking at idle, single-monitor power consumption, which has the second GPU in ZeroCore, we see power draw similar to the GTX 690, but roughly twice as high as competing single-GPU cards. Compared to the previous generation, the HD 6990, we do see a sizable improvement, though.
Power consumption immediately shot up, still with one GPU in ZeroCore, once we connected a second monitor. While it is better than cards of previous generations, it is no match for the GTX 690 (48% less power) or GTX Titan that only uses one fifth(!) of the HD 7990's power in this state. The underlying reason is that all recent AMD cards increase memory clock to full, 1500 MHz in this case, while NVIDIA stays at their single-monitor clocks and voltages, even after a second monitor has been added.
Moving on to Blu-ray, it immediately becomes clear that the HD 7990 is a power-sucking vampire during movie playback. The card sits at the end of the spectrum, even with ZeroCore power being active (which looks to be the only reason the card did not come in last). Any other card on the market will basically handle HD movie playback more efficiently.

Let's now look at the card's gaming power consumption. Here, the HD 7990 shows numbers that, honestly, are better than I expected. Overall, the card is not as efficient as other cards, like the GTX 690 or GTX Titan, but Power consumption during gaming hovers at around 300 Watts, so the 375 W limit of the power delivery circuit does not max out.
What is interesting to see is that the HD 7990 only consumes 50-70 W more power than the HD 7970 GHz Edition. Both cards run the same clocks and voltages, but the HD 7990 has an extra GPU, 3 GB of additional memory, and the PCIe bridge chip to power. AMD apparently made some good choices while working on the power consumption of the HD 7990.