Corsair Overclocking Guide Part 1: The CPU


Overclocking is one of those subjects I’m always a little antsy about with newer enthusiasts. It’s something with a storied history. Way back in the day, from the nineties into the oughts, overclocking was a means of extracting the performance of a higher-specced CPU from a budget model and essentially saving some cash. These days, though, that isn’t the case; while AMD continues to be fairly overclocker-friendly, Intel locks down their budget CPUs and isolates overclocking to specific, more expensive K versions in their lineups. It’s gone from being a way of extracting more value from an inexpensive investment to almost exclusively breaking performance ceilings.

So how does it work? To understand overclocking, you need to have a very rudimentary understanding of how computer chips are made. For this three part series I’ll be talking about CPUs, memory, and graphics cards, but the principle is essentially the same. When you look at Intel’s desktop lineup, there are twenty different models between their Core i5 and i7 series; would you believe me if I told you that the vast majority of those are all based on literally the exact same silicon?

No two chips are alike. When they’re manufactured, they undergo testing to see what speeds they can hit at what voltages. Chips that underperform for some reason or have nonfunctioning parts are binned to be lower performing models, while higher performing chips get binned as more powerful models. The net result is that the exact same silicon can produce a “lowly” Core i5-4430 or a screaming fast Core i7-4770K. This same process essentially applies to how memory and graphics cards are manufactured.

So why overclock? Because it can be fun, and because free performance is awesome. A lot of our enthusiast market is built on the back of overclocking and extracting as much performance as we can out of our hardware. With that in mind, though, remember that the hardware you buy is only ever guaranteed to run at its listed spec. When you overclock, you exceed that spec, and from there it’s a lottery. In my home system I’ve tried two different i7-4770Ks; one wouldn’t go past 4.3GHz without needing a ridiculous amount of voltage, the other gets to 4.5GHz easily but won’t budge past it. I’ve heard of i7-4770Ks that won’t even go past 4.2GHz, and the i7-4930K in my workstation is a comically poor overclocker. The point is that people in forums will tell you that you can reliably hit a certain overclock with a given chip, but you’re really playing the odds: if 80% of 4770Ks can do 4.4GHz, that still means that 20% of them can’t, and you can still wind up being the poor sod that gets stuck with a dud chip.

For overclocking, I’m just going to cover the basics. There’s a lot more fine tuning that can be done later on as you learn more and more about it, but basic overclocking is fairly simple. What you need is a chip that can be overclocked (any AMD or Intel chip with a K or X suffix, or any AMD FX chip) and a motherboard that allows for overclocking (any Intel motherboard with a Z-series chipset, most AMD motherboards). A CPU’s clock speed is calculated by a base clock (typically 100MHz) and a multiplier. So a 3.4GHz CPU would have a 100MHz base clock and a multiplier of 34.

Overclocking a CPU used to be convoluted and involved; today it’s largely just increasing the multiplier until the system isn’t stable anymore. So the knobs that you’re going to turn are the multiplier, the Vcore (the voltage going into the CPU), and the Load-Line Calibration or “LLC.” With most good motherboards you can leave the rest of the settings on “Auto.”

The performance boost you get isn’t going to be entirely free, though. Hitting higher clock speeds on your chip is going to mean increasing voltage, and increasing voltage means more heat, which in turn means that you’re going to have to keep the CPU cool. Intel’s mediocre stock cooler was already barely enough for running their chips at spec, you’re going to need something with more oomph to keep your processor from overheating when you start putting the screws to it. Even our entry level Hydro Series H55 cooler will get you a lot more headroom over Intel’s stock cooler, but if you want to extract as much performance as you can, something beefier like the H100i or H110 is going to be the way to go.

Also important to understand is that individual CPUs tend to have an inflection point. You can gradually increase clock speeds with very minimal increases in voltage, but there’s a certain point where they’re going to require much more voltage for every incremental gain in clocks. So while your chip may be able to go from its stock 3.5GHz to 4GHz or 4.1GHz without increasing voltage at all, going from 4.1GHz to 4.3GHz or so may require a modest voltage bump, and then going from 4.3GHz to 4.4GHz may require a much larger boost. Personally, I don’t like overclocking past that inflection point, as heat just becomes too much of an issue and the substantially increased voltage can significantly reduce the lifespan of the chip.

Finally, understand that if you need a 100% stable machine, you probably shouldn’t be overclocking. You can have an overclocked system that’s 100% stable, but there really are no guarantees here. Sometimes you can have an overclock that you think is totally stable, and all of a sudden your system will just up and crash for no reason, at which point you’ll either have to bump the voltage to the CPU a little or knock the multiplier down a step. You also do this at your own risk; CPUs are full of safeguards to prevent you from toasting them, but you void your warranty nonetheless. Overclocking is fairly safe these days, but I’ve fried chips from pouring too much voltage into them, so this guide is going to be pretty conservative.

Since overclocking can make your system unstable (and since we’re testing for stability in the first place), it’s a good idea to get your software ready before you dig in. You’ll want these four programs:

  • HWMonitor, which is used to monitor core temperatures.
  • OCCT, which is one of three stability tests.
  • POV-Ray 3.7.0, the second of the three stability tests.
  • PCMark 8, the third of the three stability tests.

All of these programs are free; there are paid versions but you won’t need them.

The actual act of overclocking your CPU is fairly easy and iterative. When your computer is booting, enter your BIOS by hitting the Delete key on your keyboard. Amusingly, I’ve found that backlit keyboards like our Vengeance K70, K90, and K95 are incredibly useful because the backlighting lets you know when the keyboard is detected during boot. You’ll want to use your motherboard manual to track down the three settings you need, but you’re specifically looking for the VCore Offset (you may have to set your VCore Mode to Manual first), your core multipliers, and Load-Line Calibration. On the Offset, just set it to the lowest setting above 0 you can. For Load-Line Calibration, find the highest setting, then choose one step down.

As for the core multipliers, on almost any modern processor, you can safely bump all of them up to 40 (for an effective 4GHz) to use as a starting point. From there, try to boot into Windows. If you’re successful, run OCCT for five minutes, then run POV-Ray’s benchmark. If your system remains stable, nothing crashes, and your CPU core temperatures remain within their safe thresholds, you can go back into BIOS and bump the core multipliers by one. OCCT actually includes temperature monitoring, and it’ll stop the test if your thermals are too high, but having HWMonitor running in the background is also helpful.

If your system doesn’t pass these stability tests, but thermals are still acceptable, add 0.025V to your VCore Offset and try again. If you have to add more than 0.05V to go from one multiplier to the next, you’re probably at your inflection point and heat is going to be a serious problem if it isn’t already. Safe load temperatures on the CPU cores (and these are the temperatures you’ll want to watch) are typically below 85C on Intel chips, while AMD chips vary, with the safe margin often being a much lower 65C.

When you’ve found a combination of voltage and multiplier that you’re pretty confident is stable, run the three tests in PCMark 8. PCMark throws varied workloads at your CPU and is fairly well rounded overall. If your system fails PCMark, you may need either a small bump in voltage or to back down your overclock by a step.

Ultimately, this is a quick and easy way to get some free performance. From here there’s fine tuning that can be done, but for the most part this is how I was able to get my desktop to where it is, and it’s hard to be down about a 4.5GHz Core i7-4770K.


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