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WAN show featured! LLC no longer affects vcore stability in Haswell or Devil's Canyon processors, as all the voltage regulation happens on the cpu. LLC only affects Vin (the voltage supplied to the cpu as a whole), and as far as I can tell, Vin stability has no effect on Vcore stability. More information can be found in this thread. First a disclaimer: this is my experience with Load-Line Calibration (LLC) during my overclocking. Some of the information in the post may be incorrect, although I will try to only post information which I feel is validated given my experience. I don't have any certification in making motherboards or programming, so this is simply my understanding of how this stuff works. Please remember that every motherboard manufacturer may use a different bios setting to implement LLC, so make sure that you look at what YOUR motherboard/manufacturer says about their LLC implementation. Why I'm writing this: This subject has been briefly addressed by several people on several different forums and several different overclocking guides. But a quick google search for load line calibration gave an article from 2010 (http://www.overclockers.com/load-line-calibration/) concluding that LLC was good and overclockers should use it. Other threads that come up with a google search are usually two-liners asking whether they should use LLC for their overclock, with the general consensus being yes they should. I couldn't find anything about LLC on the LinusTechTips forum, and I felt that this should be addressed. There seem to be no recent go-to beginner-level threads about LLC, and there seems to be no general understanding of what it is actually doing. This thread is intended to be an introduction to what LLC is actually doing, and why you should use it with care. Background on LLC: For those of you who don't really know what LLC is: LLC was a featured added to motherboards several generations ago to combat vdroop. Vdroop is a drop in voltage supplied to the CPU as load increases; basically when you go from idle to load, the voltage would decrease. Given the small voltage tolerance that overclockers are working with (increased voltage is proportional to the CPU frequency/multiplier that an overclock can achieve), a droop in voltage applied to CPU can make a theoretically stable overclock unstable (dropping the voltage below that required to achieve the set frequency). LLC applies additional voltage to the CPU to combat vdroop so that when switching to load, there is sufficient voltage to keep that frequency stable. So LLC is great and you want to turn it on? Yes, but... For most modern motherboards, there are different levels of LLC that you can set in your bios. At certain levels of LLC (these may be different for each motherboard), the LLC can overcompensate for this vdroop, and actually apply vboost. Vboost is when the voltage actually supplied to the CPU is above the value that you set in your bios. This can be a nice way of ensuring that your overclock will be stable, but you have to be careful, because each CPU has a death voltage (the voltage where, if applied to your CPU, it will likely die). If you are toeing the line near your CPU's death voltage to try to squeeze every last MHz out of your overclock, LLC can bring your actual voltage above this level, which is a great way of killing your CPU (or making it degrade much faster). So although LLC is great for overclockers, it should be used with care, because you may just end up killing your CPU. Now each motherboard is different, and may label their LLC settings differently, and this thread will be based on my settings on my ASUS Rampage IV Extreme. Make sure that you check your motherboard manual (and do a bit of googling for other people's experience) for how LLC is implemented in your case. (For instance, Asrock motherboards from the H77 generation had their LLC values reversed from the values that ASUS uses.) Now I had heard of all this LLC mumbo-jumbo (actually it was thecrazyrussian who told me to be careful with my overclock), and I wanted to see just what actually happened when you try different levels of LLC. So I went through my motherboard and tested each LLC setting and ramped up the set voltage, seeing what the actual read voltage was. I used a digital multimeter (just a basic one that I bought at the Source), but even that is more reliable than the values that your motherboard bios (or software) can read. Testing Setup: ASUS Rampage IV Extreme, i7 3930k, 16Gb Corsair Vengeance CL8 ram in quad-channel, XFX PRO 1000W PSU, Corsair H100i cooling. The amount of Vdroop changes with the CPU frequency, so I set my multiplier at 40 (stock is 32, and I have a stable overclock for this CPU at 45). I started at an arbitrarily chosen Vcore of 1.325V and ramped up until 1.4V (the voltage past which my CPU degrades much faster, and is considered by some to be the near death voltage of the CPU), or until the temperatures hit about 78 C. To avoid having to reboot with every voltage change, I applied all of my voltage tweaks using ASUS' AI Suite 2. Idle voltages were taken at the Windows 7 desktop with no programs open, load voltages were taken after Prime95 (small FFTs) completed its first pass. My motherboard has five settings for LLC: Regular (0%), Medium (25%), High (50%), Ultra High (75%), and Extreme (100%). My Vcore (CPU voltage) can be changed by steps of 0.005V, which may seem very small, but keep in mind that a change of 0.005V in Vcore can destabilize an overclock. Results At a LLC setting of Regular (0%), the voltage at idle was an average of -0.018V from set (idle: blue line, set: black line), the voltage at load dropped an average of -0.054V from set (red line), with a droop from idle to load of -0.036V. Immediately we can see that not enabling LLC can seriously destabilize an overclock. Moving up to an LLC setting of Medium (25%), the average voltage changes from set were -0.007V at idle, -0.023V at load, with an idle to load droop of -0.016V. The idle voltage isn't that bad, being pretty close to the set voltage, but the load droop is still more than enough to destabilize an overclock. Now up to an LLC of High (50%), the average voltage changes from set were +0.005V at idle, +0.011V at load, with an idle to load boost of +0.006V. This LLC appears to be pretty good, with the motherboard actually putting out a similar voltage to the one we set in the bios. There is a small amount of Vboost, but the magnitude is unconcerning, putting us nowhere near the death voltage of the CPU. For this LLC setting I only went to a setting of 1.380V, because CPU temperatures were becoming concerning. This is where things start to get interesting. Setting a LLC of Ultra High (75%) gave average voltage changes from set of +0.018V at idle, +0.045V at load, with an idle to load boost of +0.028V. This is hugely different from what we set in the bios, idling at ~3x and loading at ~9x the increments we can increase and decrease by in the bios. Here I stopped increasing values for two reasons: the first being that the CPU was at 77 C, and the second being that the actual read voltage was just barely below the fast-death voltage for my CPU. I was ready to stop at Ultra High, but to do my due diligence, I tried Extreme (100%) LLC. The idle voltage was +0.031V above set, and the load voltage was an insane +0.086V above set. Just switching it to load brought the voltage well above my 1.4V ceiling. I didn't even let my prime95 get to the first pass, I just took the reading and brought the computer down as fast as I possibly could. Conclusions Quite frankly I was shocked to see the effect that LLC setting has on actual voltages, especially at Ultra High and Extreme. I do understand that that every motherboard may implement LLC differently, and the Vdroop/Vboost changes may not be as incredible as I saw on my board. I can easily visualize someone trying to get the highest overclock possible, but ignoring the LLC setting (or worse setting it to extreme) and frying their CPU. I hope this thread illustrates my experience with LLC and persuades the reader that LLC should be used when overclocking, but must be used with care. Personally I chose an LLC setting of High (50%) for my overclocking, because it resulted in no Vdroop, but didn't result in enormous Vboosts. I also took into account the small observed Vboost, and made sure to never bring my voltage to a level where the Vboost would touch the fast-death voltage of my CPU. I have what I consider to be a stable overclock with this motherboard and CPU at 4.5 GHz at a Vcore of 1.325V (stable for 24h of prime95 small FFTs). Note to the reader after additional testing: Vdroop and Vboost will not behave in a fixed manner! Idle and load voltages follow a linear trend, but the slopes of those lines are not equal. Read my follow up post for more details. TL;DR: LLC should be used while overclocking, but used with care. If you don't and you're not careful, you could kill your CPU or degrade it very quickly under load voltages. It can also be chosen logically, see part 2 for more details. Read Part 2 here!