The PowerTune mechanism in AMD's Hawaii-based Radeon R9 290X and 290 graphics cards is a little different from the clock boosting schemes typically employed by GPUs and CPUs. Turbo mechanisms usually ramp up from a base clock speed that guarantees a minimum level of performance. PowerTune, on the other hand, scales back from a maximum frequency based on thermal conditions. There's no base clock speed to establish a performance baseline.
Since the new Radeons debuted, we've seen reports that retail cards are running slower than expected. Radeon R9 290X cards purchased by Tom's Hardware and one of our own readers, JohnC, maintain much lower clock speeds than the 1GHz peak advertised by AMD. Fan speeds may be part of the problem—specifically, the blowers on some Radeon cards may not be spinning fast enough. AMD says it has identified "variability in fan speeds across AMD R9 290 series boards," and that the new Catalyst 13.11 Beta9.2 drivers will ensure the blowers are running at the correct speeds.
According to AMD, the 290X's blower should spin at 2200 RPM in quiet mode. The default fan speed for the 290 is higher: 2650 RPM. The review samples we've received from AMD come pretty close to those targets. However, the XFX 290X card purchased by JohnC appears to be spinning its blower at only 1955 RPM. That's the sort of scenario the new drivers are meant to address.
The only Hawaii-based Radeons available for sale are reference units with the same AMD cooler as review samples, so I'm surprised to see so much apparent variability in fan speeds. Maybe the blowers on the affected cards came from a different batch. There certainly appears to be little room for error with the new Radeons, which run at the ragged edge of their thermal limits. The 290X even has an "uber" mode that puts the blower into overdrive to help sustain higher clock speeds.
Tom's Hardware has tested the latest Catalysts, and the drivers do reduce the performance differences between the site's 290X press sample and the Asus and Sapphire cards it purchased. However, there are still small gaps between those cards, likely due to the characteristics of their individual GPUs. The fact remains that some chips are more comfortable running at higher speeds—and at lower voltages—than others. With Hawaii so close to its limits, and with PowerTune lacking a baseline clock speed, users may have to deal with some variability in Radeon R9 290 and 290X performance.
I'm curious to see how JohnC's Radeon fares with the new drivers. We'll keep following this story as it develops.