|AMD FX-8150 Bulldozer Processor|
|Reviews - Featured Reviews: Processors|
|Written by David Ramsey|
|Tuesday, 11 October 2011|
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AMD FX-8150 Overclocking
Like Intel's Sandy Bridge, AMD's new Bulldozer processors are fabricated on a 32nm process. This means they use less power and generate less heat than the older Phenom II CPUs, which were based on a 45nm process. Less power and less heat generally means better overclocking, and the FX-8150 doesn't disappoint: I was able to reach a stable 4.8GHz on all eight cores under extended stress testing, running the CPU at 1.4V and using a Thermalright Silver Arrow air cooler. This is 200MH higher than AMD suggested was feasible for all cores "on air" in their reviewer's guide, so I feel pretty good about it! With the giant Thermalright Silver Arrow cooler, processor temperatures under load maxed out at 59 degrees at an ambient temperature of 24 degrees.
Overclockers were initially dismayed that Intel's Sandy Bridge and its supporting Cougar Point chipset removed two classic overclocking mechanisms: increasing the base clock speed and increasing the base multiplier. You can only overclock Sandy Bridge CPUs by increasing the turbo multiplier, and then only on a "K" series Sandy Bridge CPU and a supported motherboard chipset. Somewhat ameliorating these limitations was the fact that if you did have the right hardware, Sandy Bridge CPUs were capable of immense overclocks.
AMD's FX series CPUs, in contrast, are completely unlocked and the 990FX chipset does not generate the base clock for the entire system, so you have all the classic overclocking mechanisms available. Now, for most real world use, overclocking by raising the turbo multiplier is your best bet: the CPU will ramp up its clock speed under load as needed, but drop back to a lower clock speed when it's idling, using less power and generating less heat. But for my tests I wanted to be sure that the Bulldozer was pushing with its blade all the way down under all circumstances, so I raised the base multiplier to 24, which when multiplied by the 200MHz base clock resulted in a speed of 4.8GHz. I did try a 24.5 multiplier, and I could boot and run at 4.9 but the system would crash under stress testing.
The chart below shows how overclocking affected the 8150's performance on each benchmark, with the stock clocked benchmark score normalized to 1.0 and the overclocked benchmark score represented as how much faster it was than the base clocked benchmark.
The performance improvement is less than what I'd hoped, but bear in mind that the AMD FX-8150 can crank its cores up to 4.2GHz at stock clock speeds, and the difference between 4.2GHz and 4.8GHz is only 14.9%, so the observed 13.3 percent is quite close to what you'd expect from the clock speed difference.
Late note: AMD will be selling the FX-8150 in a kit bundled with a water cooler. Although there isn't an MSRP yet, AMD says the price will be "about $100" more than the CPU by itself. Benchmark Reviews received the water cooler too late to incorporate into this review, but we'll be investigating its performance in a future article.