Monday, August 5, 2013

[Article] Haswell overclocking woes - Super high temps and why that is

In the last post I mentioned that I bought a new Haswell processor - the top of the line Core i7 4770K - and a board with the Z87 chipset - Asus ROG Maximus VI Hero. We all know that retail version of Haswell CPUs don't overclock well, and luck plays a big role when it comes to overclocking. It was kinda like that in SandyBridge and IvyBridge as well, but now the weight has moved even more towards the luck factor. I wanted to believe that I was on that top 5% of the crowd that were lucky enough to get a chip that could boot into Windows at 4.6GHz with just 1.2V. Well, it turns out that I am not that lucky. But my chip isn't that bad either.

I managed to get mine up and running at 4.4GHz on all cores, 4.1GHz on "uncore", with a Vcore of 1.285V set in BIOS. Oops, sorry, UEFI. That Vcore doesn't sound too bad for SandyBridge, but for Haswell, it is a big Vcore. Not electrically, but thermally. Usually, this is the custom water cooling territory. However, the CPU managed to pass 6.5hrs of AIDA64 stress test overnight. The max temps it hit was 89C, but that's only briefly. Most of the times it was below 80C. My Silver Arrow SB-E Extreme was doing a pretty sweet job it seems. And that's not even at 100% fan speed. Just 1600RPM on average. I can go all the way up to an ear deafening 2500RPM if it deems necessary.

Reasons for high temps

First let's deal with the obvious stuff. Why does Haswell CPUs run hotter than their predecessor? There are three reasons. 
  • It uses Tri-gate transistors that don't like to scale with voltage. We saw this with IvyBridge as well
  • There is a voltage regulator module onboard the CPU, called the IVR (Integrated Voltage Regulator). That's additional circuitry and circuitry that handles voltages.
  • The die is not soldered to the heat-spreader. There is merely a thermal paste in between the die and the heat-spreader. And a very bad one at that.
Hence, as you increase the voltage when you are overclocking, the core temps go up rapidly. Don't be mistaken though: it's not heat. The heat output should be less than SandyBridge and about the same as IvyBridge. It's the temps that go out of control because the heat is not properly transferred from the die to the heat-spreader.

Solution

What's the answer? There are two. Neither of them are happy solutions though. 

First one is, lowering the Vcore. You will have to give up your current overclock. That's definitely not a happy solution. 

Second one is, delidding. Delidding means, you remove the heat-spreader, clean out the crappy thermal paste, put high quality thermal paste and putting back the heat-spreader. That's a bit adventurous and definitely voids warranty (and perhaps you won't be able to sell it back), so again, it is not a happy solution either. But if properly done, you would see a drop of about 15C by delidding. That's a huge amount. Even if you don't exploit that added thermal overhead, you will have a cool running CPU that even uses less power. (Heat causes more resistance and thus increases power consumption. On IvyBridge that was like a 30W difference at 4.6GHz. It should be similar on Haswell.)

I haven't decided if I want to delid or not. That's a big decision to make. But I will talk about how to do it on another post.
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