Gaming Power Consumption Details
Measuring Power Consumption
We’re using a current clamp to measure power consumption at the external PCIe power cable and, using a special PCB, directly at the PCIe slot. These measurements are recorded in parallel and in real time, added up for each second, and logged using multi-channel monitoring along with the respective voltages. All of this results in a representative curve over the span of 10 minutes. That's all we really need, since these cards reach their operating temperatures relatively quickly.
The curve isn’t just representative; it's also exact. Measuring system power introduces bias, since a number of factors can affect consumption other than the graphics card. A faster GPU might cause the CPU’s power consumption to go up as well, for example, since a limiting factor holding it back is gone.
We're using Nvidia's GeForce GTX 780 as the “competitor”, since its performance comes the closest to Radeon R9 290, making it a good basis for comparison. You'll also find a GeForce GTX 770 and Radeon R9 280X in the line-up as well.
AMD Radeon R9 290 Gaming Loop Power Consumption
The feedback we received on the forums after our AMD Radeon R9 290X launch article prompted us to question if the efficiency of Hawaii-based graphics cards changes if the temperatures are purposefully kept low. For this reason, we’re presenting three sets of results for the Radeon R9 290.
Default Mode and Settings with Catalyst 13.11 Beta v7
This mode is similar to the Radeon R9 290X’s Quiet mode with its 40 percent maximum fan speed. Let’s have a look at a 10-minute benchmark run consisting of Metro: Last Light looped at maximum settings. It’s interesting to see that the power consumption is significantly higher before the target temperature is reached, after which time it drops noticeably. The average in the graph only takes the values after the limiter kicks in to make the outcome more representative of real-life usage.
Temperature Target of 70 °C and Maximum Fan Speed of 80 Percent with Catalyst 13.11 Beta v7
The second benchmark run shows the card’s power consumption after setting the target temperature to 70 °C and the maximum fan speed to 80 percent, while leaving the power limit alone. Better cooling gets rid of the peak and smoothes out the curve. The power consumption is higher overall, though. We aren’t exactly in love with a very busy chart that’s characterized by many erratic jumps, which can only partially be explained by the wildly jumping GPU clock frequency.
The massive power consumption drops shown by the force-fed Radeon R9 290 and its more constant clock rate curve confirms the theory that reaching the target temperature results in frantic regulation attempts by the power limiter, which leads to the observed jerkiness.
Default Mode and Settings with Catalyst 13.11 Beta v8
Right before the 290's original launch date, AMD told us it was pushing back the introduction to accommodate a new driver that was supposed to bolster performance. In reality, the driver update is a compromise between the Quiet and Uber modes of the already-launched Radeon R9 290X. A 47 percent maximum fan speed and a target temperature of 95 °C is exactly in the middle between the two modes. Let’s take a look at the power consumption and the actually achievable clock frequencies.
Two things are interesting here. First, the power consumption peak is gone, and the card levels off at exactly the same point as the force-cooled board once the temperature limit is reached. Second, the clock frequencies are similarly consistent and only slightly lower than those of the much cooler card. Looking at these results, and taking into account how often AMD asked us for our impressions of the Radeon R9 290’s cooler and performance, the new driver's trick becomes clear: you get a cooler, but louder, graphics card with a small performance boost.
Nvidia GeForce GTX 780 Gaming Loop Power Consumption
Now, how much power does the GeForce GTX 780 need to achieve similar performance? Just like before, we’ll help the card out a bit by lowering its temperature to 70 °C, which we achieve by increasing fan speed.
The first thing to note is that the GeForce GTX 780’s curve also sports a small peak when the temperature target is reached. This peak is a lot less pronounced than the 290’s, though. Cooling the card down barely changes the curve.
What makes this comparison different from AMD's card is that the curve is a lot smoother and doesn’t show the same extreme power consumption fluctuations. Even more interesting are the minimum and maximum power consumption, which stay the same when the card is cooled down. Only the average increases.
Nvidia GeForce GTX 770 and AMD Radeon R9 280X Gaming Loop Power Consumption
Let’s take a look at a couple of lower-end cards. This will be important later when is comes time to look at efficiency.
The differences are massive in light of the fact that both boards performance very similarly. This nicely demonstrates just how much of a jump ahead AMD has taken with this graphics card generation.
AMD is doing a great job catching up, but it isn’t quite there yet. According to our measurements, the former 40 W difference between the two rebranded graphics cards is down to approximately 20 W separating R9 290 and GTX 780. Then again, slightly higher gaming performance might be something to take into account as well.
Either way, Nvidia’s power consumption curves are smoother and free of short, sudden drops. This should give AMD a reason to tune its drivers a bit more.