Intel Core i7-6900K: Overclocking, Power & Temperatures
Base Clock Frequency, Turbo Boost & Overclocking
Intel’s Core i7-6900K is the -5690X's direct replacement. The company's least-expensive Broadwell-E models have six cores each, while the -6900K and -5690X sport eight. The Core i7-6900K’s stock base clock rate is 3.2GHz; Intel has to turn this down to fit in the platform's 140W TDP with eight cores active.
No matter how much voltage we pushed through this CPU, our highest stable overclock was 4.3GHz. Beyond that, the system wouldn’t even boot up.
Again, let’s take a look at the individual core frequencies for the three configurations we tested. Despite a 3.2GHz base clock rate, Turbo Boost pushes the CPU to 3.7GHz in lightly threaded workloads. Our sample managed to maintain this frequency across all cores during the stress test. One core even reportedly hit 4GHz.
Core Voltage Necessary For A Stable Overclock
The 1.38V needed to hit 4.3GHz isn't particularly impressive. This improves at 4GHz. Then again, that's barely much higher than Intel's maximum Turbo Boost bin.
Overclocking beyond 4.0GHz results in a massive power consumption increase, and even 1.5V can’t get the CPU over 4.3GHz.
Resulting Power Consumption
Unless a game scales perfectly according to available resources, the power consumption is similar to what we saw from the six-core models. Intel's Core i7-6900K doesn’t really draw any more power than the lower-end implementations of Broadwell-E; it stays under 100W all the way to 4.0GHz.
It's only when all eight cores are fully utilized that the Core i7-6900K really gets going. For the first time in our review, we record a result greater than 200W. This has us curious where the flagship -6950X is going to end up.
Temperatures During Continuous Operation
Again, we averaged all of the cores together as reported by the sensors for each measurement interval and split them into our various workloads. The results reveal a general problem with Broadwell-E: the 14nm process makes for denser CPUs, which are harder to remove heat from quickly. Our high-end water cooling setup has more trouble cooling the Core i7-6900K than it did with the -5690X, which consumed about the same amount of power at 4.5GHz.
Also, the Core i7-5690X ran stably up to 4.8GHz, and it was possible to get it going at 5.0GHz with a core voltage of 1.5V. Intel's Core i7-6900K can't even come close to matching those numbers.
Bottom Line
At the risk of sounding like a broken record, the Core i7-6900K is reasonably efficient at its stock frequency. Overclock it, though, and this changes quickly and drastically. Every 100MHz step up comes at the cost of a hefty core voltage increase. And it can’t be overclocked beyond 4.3GHz at all, no matter how much voltage you add.
Thus, the Core i7-6900K only makes sense if you're using software that scales perfectly with core count. It could be considered suitable for pure gaming workloads, as long as those games don’t just use a single thread.
But if you're an overclocker, the Core i7-5930K is a better alternative to the -6850K, and Intel's Core i7-5960X trumps the -6900K. At the same clock rates, Intel's Haswell-E generation is easier to cool.
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