|Intel Core i7-3820 Extreme Edition CPU|
|Reviews - Featured Reviews: Processors|
|Written by Hank Tolman|
|Tuesday, 06 March 2012|
Page 15 of 17
Core i7-3820 Overclocking
I have to tell you, without the K or the X moniker at the end of the i7-3820, I was initially very skeptical of its overclocking ability. Sandy Bridge doesn't have the greatest track record in my mind with its ability to easily overclock. For the most part, you are limited to overclocking just the turbo boost. I was pleasantly surprised by what I found, however.
To get started, let's get into some background on Sandy Bridge overclocking. It's important to realize that, for the most part, Sandy Bridge CPUs are locked at their base clock speeds. Any Sandy Bridge CPU that supports Turbo Boost is partially unlocked simply due to the fact that they support Turbo Boost. Turbo Boost in itself is an overclock, boosting the base clock up to higher frequencies. All Turbo Boost enabled Sandy Bridge GPUs can be overclocked to run 400MHz higher than their base Turbo Frequencies. K and X series CPUs have a limited unlocked Turbo Boost and fully unlocked memory, power, and graphics capabilities. Obviously, graphics overclocking isn't something that comes into play on the Sandy Bridge-E CPUs.
To explain this further, I'll talk specifically about the Core i5-2500 and i5-2500K processors. The i5-2500 has a base frequency of 3.3GHz and a Turbo Boost Frequency of 3.7GHz with 1 active core, 3.6GHz with 2 active cores, 3.5GHz with 3 active cores, and 3.4GHz with 4 active cores. With the limited unlock capabilities of this CPU, you could boost each of those Turbo frequencies by an additional 400MHz, making the maximum overclock 4.1GHz if only 1 core is active. The i5-2500K is virtually the same, except for the fact that the unlocked K-series CPU has a limited unlocked modifier that lets it go above that 400MHz threshold. It's still limited, however, so that the max overclock you could potentially achieve is 5.7GHz with 1 active core.
While the two, higher end Sandy Bridge-E CPUs are both X or K-series CPUs and are thus unlocked, the i7-3820 is not. This makes it potentially more difficult to overclock than the other Extreme Edition CPUs. Since the i7-3820 uses Turbo Boost and has a max Turbo of 3.9GHz, it reasons that you should be able to overclock to 4.3GHz by just using the standard, limited multiplier adjustments available with any Turbo Boost enabled Sandy Bridge CPU. Remember that the 4.3GHz mark would only be for a single active core. With all four cores running, the best you should be able to see is 4.0GHz. Pretty boring stuff for an Extreme Edition CPU, right?
Luckily for us, Sandy Bridge-E made some other changes that affect overclocking. While normal Sandy Bridge platforms use a bclk of 100MHz, the Sandy Bridge Extreme can use a bclk of 100MHz, 125MHz, 166MHz, or 250MHz. Just crunching the numbers, if that 4x the bclk ratio is in effect, then with the multiplier at 43, as it was for the single core turbo overclock with the 100MHz bclk, we are looking at a potential overclock of 5.375GHz with a bclk of 125MHz, 7.138GHz at a 166MHz bclk, and 10.75GHz at a 250MHz bclk. Obviously, pushing the bclk to 250MHz, or even 166MHz, is really out of the question. Even using the base clock as the multiplier at 3.6GHz, you're trying for a 5.9GHz overclock with the 166MHz bclk. But 125MHz bclk is right up our alley.
Just by pushing the bclk up to 125MHz, you are already looking at a base overclock to 4.5GHz. That's quite respectable, considering that would run on all 4 cores as opposed to the standard max of 4.3GHz on a single active core. To get all I can out of the i7-3820, I'll probably need to change some of the other settings besides just the blck frequency. I used the ASUS Rampage IV Formula motherboard for this overclock. To find out more about the specific settings I tweaked, watch out for my review of that motherboard. I'll tell you just what I did to get to 4.75GHz on the i7-3820.
The X79 chipset brings a separate base clock back into the overclocking world, so this time-honored mechanism is again available. The CPU itself adds a new twist: in addition to increasing the voltage to the chip to support higher speeds, you can now increase the sustained maximum and burst maximum current draw as well.
A nearly 32% increase in base clock speed improved performance on average by 24% during our tests. I'd call that very successful for a locked CPU. I'd bet with a little more tuning we could probably see 5GHz on the i7-3820 without many issues. Remember that each component is different and each individual CPU or motherboard will result in different overclocking speeds and capabilities.