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Power consumption
We measured total system power consumption at the wall socket using an Extech power analyzer model 380803. The monitor was plugged into a separate outlet, so its power draw was not part of our measurement. The cards were plugged into a motherboard on an open test bench.

The idle measurements were taken at the Windows desktop with the Aero theme enabled. The cards were tested under load running Left 4 Dead at a 2560x1600 resolution, using the same settings we did for performance testing.

Even the Radeon HD 5870 consumes less power than the GeForce GTX 285, so there's really no contest between the Nvidia card and the new 5850. AMD's DirectX 11 offerings both have about the same idle power draw—a testament to Cypress' power efficiency—but the 5850 draws a good 36W less than its big brother under load.

Noise levels
We measured noise levels on our test system, sitting on an open test bench, using an Extech model 407738 digital sound level meter. The meter was mounted on a tripod approximately 8" from the test system at a height even with the top of the video card. We used the OSHA-standard weighting and speed for these measurements.

You can think of these noise level measurements much like our system power consumption tests, because the entire systems' noise levels were measured. Of course, noise levels will vary greatly in the real world along with the acoustic properties of the PC enclosure used, whether the enclosure provides adequate cooling to avoid a card's highest fan speeds, placement of the enclosure in the room, and a whole range of other variables. These results should give a reasonably good picture of comparative fan noise, though.

The 5850's lower power consumption pays off, allowing for much lower noise levels under load. The Radeon HD 5850 is nevertheless a tad louder than the 5870 at idle, although it still does better than the GTX 285 across the board.

GPU temperatures
For most of the cards, we used GPU-Z to log temperatures during our load testing. In the case of multi-GPU setups, we recorded temperatures on the primary card. However, GPU-Z didn't yet know what to do with the 5870, so we had to resort to running a 3D program in a window while reading the temperature from the Overdrive section of AMD's Catalyst control panel.

The Radeon HD 5850 runs considerably cooler than either the 5870 or the GeForce GTX 285—an unexpectedly strong showing, seeing as the 5850 has a smaller cooler than the 5870 and lower noise levels under load. What a refreshing change from the blistering-hot temperatures of previous high-end cards.