Given that this is a "speed demon" architecture and that AMD managed a Guinness world record frequency of 8.4GHz using an FX-8150 cooled with liquid helium, we were really looking forward to doing a little overclocking with our copy of the FX-8150. We didn't have any dangerous liquids in play, but we did have a fairly beefy tower cooler, at least. We set our mobo to use its most aggressive fan speed profiles and fired up AMD's Overdrive software, which makes dialing up new speeds on an unlocked CPU like this one a snap, to see what we could do.
Our starting point was the stock operation of the chip. Our FX-8150 runs at 3.6GHz and 1.2625V by default. When Turbo Core kicks in, the CPU ranges up to 1.4V and 4.2GHz. We figured we'd begin at just 200MHz beyond that top Turbo speed, 4.4GHz, at 1.4V. Seems like an easy first step, right? When we fired off Overdrive's CPU stability test, however, it quickly came back with an error. We had to raise the voltage to 1.425V in order to get the chip to pass just three minutes in that stability test. The rest of our overclocking work log looked like so:
4.6GHz, 1.425V - BSOD
4.6GHz, 1.4375V - Error
4.6GHz, 1.45V - AOD crash
4.6GHz, 1.4625V - AOD crash
4.6GHz, 1.4625V - AOD crash
4.5GHz, 1.4375V - AOD crash
4.5GHz, 1.45V - Error
4.5GHz, 1.4625V - AOD crash
Yep, 4.4GHz was about it. Perhaps we were a little timid, but raising the voltage beyond 1.465V on a brand-new, pre-release 32-nm processor felt like asking for trouble to us, especially with just air cooling. Then again, the crashes and errors we were seeing came quickly, well before the chip had a chance to heat up beyond the capacity of our cooler. We'd almost surely run up against a frequency limitation in the chip—and that's unusual. CPU these days tend to be primarily thermally constrained, and you can usually push them a fair ways past their default frequencies before running into stability issues.
Worried that we weren't reaching our chip's full potential, we pinged AMD PR on the matter, who pointed us to a section in the reviewer's guide (a document we shamlessly ignore after extracting any useful info) that suggests 4.5GHz is a reasonable expectation for FX-8150 overclocking with an air cooler. We also discovered, at the same time, that AMD had disabled three of the chip's four modules during the Guinness World Record run. That's not something we'd expect, you know, real users who care about performance to do.
The FX-8150's performance does appear to scale well with clock frequency increases. Had AMD been able to ship a Bulldozer-based part at close to 4.4GHz, the story told on the preceding pages might have had a different feel to it.
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