Power Consumption: Gaming
It took quite a bit of experimentation to find a realistic and repeatable gaming workload that'd allow us to generate meaningful power readings. Fortunately, we found what we were looking for while running the benchmarks for our 2014 VGA Charts: Unigine Heaven. Once we switched over to a platform that wasn't processor-limited, we started seeing consistent GPU loads in the 95% range, giving us the power levels expected from most of our benchmarked games. These tests happen at 1920x1080 in full-screen mode, using the Ultra preset, normal tessellation, and 2x AA.
AMD's Radeon R9 295X2 draws less power than two Radeon R9 290X cards together, amazingly enough. We checked with AMD, which confirmed for us that the dual-GPU board's chips are specially-binned. Presumably, that means the processors are lower-leakage parts, though it's also possible that more effective cooling helps bring down consumption compared to the hot-running reference design. After all, we've seen the 290X's power use drop 30 W just from a better heat sink and fan.
The two-generation-old Radeon HD 6990 pulls way more power from the PCI Express slot, with peak values that exceed the PCI-SIG's 75 W specification.
AMD’s Radeon HD 7990 turns out to be more frugal than two single-GPU graphics cards, drawing less power from the motherboard’s PCI Express slot compared to the Radeon HD 6990. But it also tends to throttle back after reaching a certain thermal limit.
Zooming In For More Detail
A sampling rate of 1 μs is as precise as we're able to get. It's impossible to start each card's test at exactly the same time when we're zoomed in this far. Still, the charts are pretty definitive: the Radeon HD 7990 throttles slightly after hitting its temperature ceiling, demonstrating the most inconsistent curve progression, followed by the extremely hot Radeon HD 6990. Meanwhile, the Radeon R9 295X2 runs at a comparatively low temperature, giving us the most stable chart.