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TweakTown's Ultimate Intel Skylake Overclocking Guide

By: Steven Bassiri | Guides | Posted: Dec 21, 2015 3:11 pm

Order of Operations




The flow chart is designed to get you to your targets and to spell out how you overclock. First you aim for the CPU core frequency, then add in FCLK (it is very easy to OC the FCLK), then Cache, and then memory. You can either overclock with multipliers (recommended for K-SKU CPUs) or BCLK (only way to OC non-K SKUs). If you overclock with BCLK then keep in mind BCLK increase will increase the CPU, Cache, FCLK, and Memory speeds. Remember that temperature is your ultimate speed limit (around 80-85C should be your maximum temperature under very heavy stress tests like IBT or Prime95).



Notes about Non-K SKU Overclocking


There are two ways to overclock frequency, either by increasing the multiplier or by increasing the BCLK. On "K" SKUs both the multiplier and BCLK are fully unlocked, but on "non-K" SKUs, Intel locked both. It turns out that while multiplier overclocking is fully locked down on "non-K SKUs", BIOS engineers have found a way to unlock BCLK overclocking. This recent development has many people very excited because now you can theoretically overclock all SKUs. There are a few caveats.


First, you must watch out and lower other multipliers because BCLK overclocking increases the final frequency of all domains (Core, Cache, FCLK, and Memory). Second, these new BIOSes are not perfect because the changes that allow overclocking not only screw up temperature sensor reporting but also break power savings features (your CPU will always run 100% frequency). Third, overclocking the BCLK can introduce jitter and might even require more VCore for stable overclocks than multiplier overclocking. Fourth, Intel does not support this, and it might be reversed soon. These issues might be mitigated in coming UEFI releases, but Intel might fight this by implementing locked UEFI updates, which do not allow flashing back to previous versions after upgrading.


The good news is that the BIOSes are already out there in the wild, and you can get away with overclocking non-K SKUs. However, if you have the money, I would recommend sticking with K-SKUs for 24/7 overclock at this time (because of BETA BIOSes with broken power savings features).



Base Clock and Multipliers


BCLK (Base Clock) x Multiplier = Frequency | e.g. 100MHz x 45 (CPU Multiplier) = 4.5GHz (or 4500MHz)




Skylake offers control over the CPU Cores, Cache/Uncore, Memory, FCLK, and the iGPU frequency domains. This guide won't cover the iGPU, but overclocking the iGPU is pretty straight forward just like CPU Core overclocking. The chart above displays how the base clock (BCLK) is multiplied with the multipliers of different CPU domains (Core, Cache/Uncore/Ring, Memory, and FCLK) to produce the final frequencies of each domain. The voltages shown are what you need to change to stabilize the different frequency domains after overclocking, and I will go into detail later. It is important to note that the FCLK is a minor frequency, the CPU cores and what people refer to as the cache/uncore/ring share the same input voltage, and the memory is impacted by multiple voltages.




This guide utilizes five Z170 motherboards from five different manufacturers, what makes these boards special is that they are all primarily focused on overclocking. I have gone and found the equivalent settings in each manufacturer's BIOS and posted them in the image above. Many of the same buses are labeled differently depending on the manufacturer.BCLK and FCLK are labeled the same thing on all boards, but FCLK's effective clock frequency is called System Agent Clock in HWinfo (one of the few programs that report it).


While all boards have the ability to run 10x FCLK multiplier, EVGA's motherboard always runs at 10x and the option isn't present to lower it. I use certain terminology such as "Multiplier" to simplify things because you multiply these against the BCLK, but "Ratio" is the correct technical term. Many manufacturers call the cache/uncore/ring multiplier either cache or ring, and GIGABYTE calls it the uncore multiplier, but they all effectively control the speed of the cache, so I will call it the "Cache" from here.


I also want to take a second to discuss the DRAM/Memory frequency. The DRAM frequency is interesting because it is simple to set, but not as straightforward as you might think. On some boards, you have the ability to pick multipliers based on either a 100MHz or 133MHz bus, and the simplest way to visualize it is as a 1.00x or 1.33x multiplier for the DRAM/memory multiplier. Using 100MHz offers memory multipliers up to 31x, utilizing 133MHz offers 41.33x (Intel's maximum for Skylake). Since the setting does not affect the actual BCLKfor other domains and since you might increase the BCLK, thinking of the setting as an extra multiplier is just easier. So why do they give you the option? Some lower-end multipliers can work with either 100MHz or 133MHz, and sometimes that multiplier might work better with either 100 or 133.

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