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In search of higher frequencies
These days, amazingly enough, motherboards will overclock your processor for you. I've been aware of this fact for a while, especially since Geoff has been testing auto-overclocking features in motherboard reviews, but I've never actually bothered to try them. Not for years, at least, since those features were in their infancy and didn't do an especially good job.

You see, I have mad skillz involving multiplier and core voltage settings. I can change both variables at once in the BIOS, yo. F10 and it's on, friend.

But I figured this time around, I'd give MSI's OC Genie button a try. Seems like a gimmick, putting a push-button right on the motherboard itself that says "overclock this thing," but the actual concept appears to be sound in theory. MSI maintains a set of profiles for common CPUs and will invoke a fitting profile when you press the OC Genie button. What you'll get probably won't be the highest possible speed for your processor, but it should be a reasonably decent overclock with a high probability of success. Why not start there?

I hit the OC Genie button, powered on the system, and BAM! Error message. Overclocking failed. Press F1 for the BIOS menu and whatever.

I made several more attempts, but no dice. The board threw an error every time I tried to boot with OC Genie enabled. I'm not sure what exactly the problem was, because this feature is kind of a black box. Were the memory timings too aggressive? Did it need a little more CPU voltage? Impossible to say.

Being the curmudgeon that I am, I brushed off this problem with a shrug and went to work in the firmware menus myself. Who needs a genie, anyhow? I've got this.

To be clear, what I've got is a really simple approach to overclocking an unlocked CPU: strap on a big-ass tower cooler, crank up the multiplier to something plausible, and raise the CPU core voltage as needed. Repeat the mult and voltage tweaks until something breaks.

With a little coaxing, I was able to get the retail Core i7-4790K running and reasonably stable at 4.8GHz and 1.32V.

I tried for 4.9GHz, and the chip was able to boot into Windows at that speed, but it quickly crashed when I started up our Prime95 load test. I tried raising the voltage in steps, going as high as 1.424V, but the chip just wasn't happy at that clock speed.

4.8GHz at 1.32V ain't bad. We were able to benchmark our pre-release sample of the 4790K at 4.7GHz, but it needed 1.45V to get there, which is quite a bit of juice for a 22-nm processor. And that earlier 4790K was a little iffy at 4.7GHz. Given everything, I'd call this retail chip 200MHz better, if you're looking for a realistic overclock for long-term use. (Those retail CPU voltages, by the way, come from MSI's monitoring software. I found that if you asked the board for 1.3V in the firmware, you'd get 1.32V. Ask for 1.35V, you get 1.368V. And so on. It errs on the side of more juice, which is a little scary when you're hitting the limits of your chip or cooler.)

That clock speed improvement isn't gonna set the world on fire, and this one sample isn't enough to establish any sort of a trend. Still, every data point we've seen points to something in the range of 4.7 to 4.8GHz being the most common limit for a Devil's Canyon CPU—which is awfully similar to a regular Haswell K-series part.

And, you know, it's really fast.

With the retail CPU at 4.8GHz and running Prime95, our Z97 MPower-based test rig drew about 210W under load at the wall socket. CPU temperatures peaked at about 80°C. The system's power use dropped down to about 54W at idle on the Windows desktop, which is almost exactly what Geoff saw from the Z97 Gaming 7 with a stock-clocked, default-voltage processor.

It may well be possible to squeeze even higher clock speeds out of a Devil's Canyon CPU with extreme cooling and the like, but that is a question for the dudes with liquid helium pots. I am not one of those dudes.

That said, I'm gonna geek out over these things in my own way soon, with broader performance testing of a whole range of the latest CPUs. That's a task we've neglected for too long around here, and I intend to rectify the oversight. Stay tuned for more CPU coverage coming up shortly.TR

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