Skylake Overclocking Unlocked - Extract maximum performance from non-K series Intel 6th-gen CPUs

Skylake Overclocking Unlocked - Extract maximum performance from non-K series Intel 6th-gen CPUs

Get the most from your machine - without have to buy a K-series CPU!

Until now, PC enthusiasts who wanted to push their Intel Skylake CPU (aka 6th Gen Core) beyond the speed printed on the box had to buy one of the special K-class CPUs along with a Z170-chipset based motherboard. This combination was officially sanctioned by Intel to allow overclocking, with the CPU’s unlocked multiplier making it a breeze to push these chips over and above their rated speeds. If you didn’t own a K-class CPU with the relevant motherboard, you were stuck with the default speed of your chip… until now. As we saw with the last generation of CPUs, a batch of hacked motherboard BIOS updates have enabled overclocking across every single Intel Skylake CPU, regardless of whether or not it’s part of the K-class. Before we show you how to do this, let’s delve into the muddy waters surrounding this issue. 


Intel probably isn’t too happy about the ability for all of its chips to be overclocked, as it means users no longer have to pay the higher price of a K-class CPU. It also means that much more affordable chips can now compete with their most expensive models; why spend $520 on an i7 6700K when you can buy a $275 i5 6500 that will run even faster than the default speed of the 6700K?  


The news that non-K chips could be overclocked first leaked in December of last year, with users of special Supermicro BIOS’ able to push their chips to higher speeds despite the locked multiplier. This new BIOS didn’t magically unlock the multiplier on non-K chips; instead it allowed the user to push up the base clock (BCLK). A CPU’s overall speed is calculated by multiplying the BCLK by the multiplier, so increasing either one will increase the speed of the CPU. All Intel CPUs have a BCLK of 100MHz, with only the multiplier changing. BCLK overclocking isn’t new, but in the past we were limited to increasing this by a maximum of 5%, as it was linked to the DMI and PCIe buses. Pushing the BCLK too high meant that both the DMI and PCIe buses were running way out of spec, causing the system to crash.

However, with Skylake Intel introduced individual reference clocks for these various buses, meaning it’s possible to increase the BCLK without pushing the other buses beyond their limits. This ability to increase the BCLK so greatly wasn’t included with the original range of Z170 boards, but Supermicro’s release of a hacked BIOS suddenly made it possible to push it by up to a whopping 70%.


It wasn’t long before ASRock joined the party with a hacked BIOS for their boards, and other manufacturers soon followed suit. Yet it seems that Intel has put pressure on motherboard makers not to do this since then, as it’s impossible to find these special BIOS versions on the official motherboard websites. From what we’ve heard, Intel can impose certain pressures on companies who break the terms of service that stop them selling products than can overclock non-K CPUs; these could be fines, higher prices, lower co-marketing budgets or even reduced allocation of silicon. We’re not sure exactly what Intel is doing to stop these BIOS spreading, but they’re doing something, as we asked several large makers about the leaked BIOS. MSI refused to comment at all, while Asus told us that “No Asus products will ship with non-K OC capability/feature due to the inherent drawbacks of the implementation and the fact that this is not officially endorsed by Asus.” Gigabyte echoed Asus’ sentiments, stating that “We won’t have it on official download site nor do we mention the ability in beta bios that supports it.” Yet all of these companies sell Z170 boards that support non-K overclocking, provided you know where to find the right BIOS – on community websites. 

When we asked Intel about the matter, and whether they would introduce microcode in their Skylake chips to halt this ability, they gave us a very short reply, claiming “Intel does not recommend overclocking processors that have not been designed to do so. Intel does not warranty the operation of the processor beyond its specifications.”

So it appears nobody officially wants to talk about this new form of overclocking, yet it’s out in the wild and taking place. It seems that any Skylake CPU can be overclocked, but it appears that it’s still limited to Z170 motherboards. 

When we asked Gigabyte about why this is, they replied that the H and B series of motherboards need a special buffer chip to increase the BCLK effectively. There’s also the matter of the power and voltage design on low-end boards, which aren’t as stable as those found on the Z170.


If you’re going to overclock a Non-K Skylake CPU, there are a few caveats to bear in mind. For starters, as with any overclock, you risk damaging the CPU. Intel won’t cover the warranty on Non-K CPUs that have been damaged whilst overclocking, but then again there’s absolutely no way to prove that this is how a CPU was damaged. Just saying. The easiest way to limit the risk of damage to the CPU is by keeping the voltage as low as possible; increasing it too high is the number one way of frying an overclocked CPU. Secondly, you’re going to need to upgrade the cheap Intel cooler that comes with the CPU – a dedicated overclockers heatsink is a must, especially due to the additional voltage that is necessary.

When overclocked, Non-K CPUs automatically have their integrated GPU disabled, so you’re also going to need a dedicated graphics card. The temperature monitoring will also be buggered, with the chip reading 100C or other crazy temps, so you’ll need to disable any features on your mobo that shut off the chip if the temperature goes too high. Most power-saving features, such as C-states, will also be disabled, so the overclocked CPU will always be running at top speed using full power. Finally, and this is a biggie for those who do a lot of media transcoding, scientific or financial applications, the Intel Advanced Vector Extensions (AVX) performance plummets. We’re not exactly sure why this is, but gamers and general desktop users shouldn’t be fussed about this, as these kinds of scenarios don’t use the AVX instructions. 

As you can see, overclocking Non-K chips has more limitations than K series chips, but we think it’s a worthwhile trade-off if you’re able to run your $260 i5-6400 at 4.5GHz! 
Also, the issue of accurate and reliable temperature monitoring can be gotten around by buying an external temperature monitor, which allows you to stick a probe near the CPU. 


Now that you know the warnings and limitations, let’s take a look at the actual process of overclocking a Non-K Skylake CPU. For our test we used a Gigabyte Z170MX Gaming 5 motherboard with the special F4D 8A09AG0Q BIOS, dated 8th of Jan. Intel kindly lent us an i5-6500 CPU, which has a default multiplier of 36, resulting in a top speed of 3.6GHz. Corsair’s H80 All-in-One cooler was tasked with handling thermal duties, while twin sticks of Crucial Ballistix DDR4 memory supplied 16GB of system memory. Two more Corsair SSDs held our Windows 10 operating system and benchmarks. 

Please note that the directions that follow are specific to our motherboard – different manufacturers use different BIOS layouts and terminology. However, you should be able to find the same settings on your motherboard, but they may be in different menus and with slightly different wording. 

1. First things first, you’re going to need to dig around the Internet to find the right BIOS. As motherboard makers aren’t officially hosting these on their sites, you’ll need to do some Googling to find it – the chances are that if you’re running a Z170 board, there should be a hacked BIOS that allows BCLK overclocking. Once you’ve found the BIOS, stick it on a USB thumbdrive, plug it into your motherboard and head into the BIOS as it boots (usually hitting delete or F1 does this). From here you should find an option to flash your motherboard’s BIOS. Select the new BIOS version and let the software do its job. Reboot the PC, and run a quick benchmark to ensure everything is working and stable as is. We use 3DMark Fire Strike, set to looping mode, and let it run for 30 minutes – if it doesn’t crash, it’s time to start tweaking. 

2. Now it’s time to increase the voltage on the CPU. At stock, our i5 6500 has a voltage of 1.145V, so we’re going to increase it to 1.35V, which is a relatively safe voltage for our CPU with this cooler. Head to the area of your BIOS pertaining to voltages; on our board it was called ‘Advanced Voltage Settings’. Then select the CPU Core Voltage Control, and find the CPU Vcore setting in this screen. Manually type in 1.3V, then hit F10 to save and reboot. Head back into the BIOS. Now we want to set the Vcore Loadline Calibration. Once again head into the ‘Advanced Voltage Settings’, and then select ‘Advanced Power Settings’. Change the value of the ‘CPU Vcore Loadline Calibration’ to High.

3. It’s time to disable all of the power saving settings, which can interfere with the overclock. At the main BIOS screen, head into the section called ‘Advanced Frequency Settings’, then select ‘Advanced CPU Core Settings’. Scroll down until you find the CPU power saving features, beginning with ‘CPU Enhanced Halt (C1E)’ and change this to disable. Then change all of the following settings to disabled: ‘C3 State Support’, ‘C6/C7 State Support’, ‘C8 State Support’, ‘CPU Thermal Monitor’ and ‘CPU EIST Function’. Hit F10 to save the BIOS settings and reboot. 

4. Now head into the BIOS again, and go to the ‘Advanced Frequency Settings’, then head to ‘Advanced CPU Core Settings’. Change the ‘CPU Clock Ratio’ (aka the CPU’s multiplier) to the maximum supported by your CPU at default speed, not Turbo speed. In the case of the i5 6500, this is 32, as the CPU has a default speed of 3.2GHz. Now change the ‘Uncore Ratio’ to the same value. Hit F10 to save and reboot, then head back into the BIOS.

5. It’s time to see your CPU fly! We’re going to adjust the BCLK, as well as the system memory multiplier, as the system memory is tied to the BCLK. Increase the BCLK and your system memory speed will increase, so we need to lower its ratio to something within range of what your memory kit can handle. Note that around 2800MHz is about as high as you want your memory to run when doing this form of CPU overclocking. From the main overclocking menu, go to the ‘Advanced Frequency Settings’ and change the ‘CPU Base Clock’. The amount to change it to depends on your CPU. We are going to aim for an initial overclock of 4.4GHz, so therefore we divide 4400 by the multiplier of 32, giving us a BCLK value of 138MHz. Just below this you’ll see the ‘System Memory Multiplier’. If we don’t touch this, our memory will be running at 3312MHz due to the increase in BCLK, so we’re going to lower the memory multiplier to 18, giving us a memory speed of 2484MHz. Cross your fingers, and then hit F10 to save and reboot. With any luck, you’ll be able to boot into Windows

6. As luck would have it, it appears our i5 6500 was a bit of a dud, as it refused to boot at 4.4GHz. So we rebooted, and headed back into the screen to adjust the BCLK, instead aiming for a 4.2GHz overclock. We achieved this by using a BCLK of 131MHz, and then adjusted the memory multiplier to keep the memory running as close to 2400MHz as possible. To our delight, the system booted into Windows perfectly!


7. Now it’s time to test for stability. Due to a bug with Skylake, we don’t recommend using Prime95, as even default speed Skylakes have been shown to crash this benchmark. BIOS updates are slowly coming out that fixes this, so check your manufacturer’s site to see if yours is ready. Instead, for now we’re sticking with 3DMark Fire Strike in looping mode. We ran this for an hour without any crashes – it’s better to keep it running even longer if possible, but we were limited in time. 

Unfortunately our i5 6500 refused to budget past 4.2GHz, which is only a small 17% increase over the default speed. However, it seems most 6500 chips are able to hit 4.5GHz without too much trouble, while even more affordable chips are hitting 4GHz to 4.2GHz with ease. It’s really a lottery, as these chips aren’t picked for their overclocking ability, unlike the K-series are supposed to be. Good luck with your Skylake overclock – hopefully a 30% overclock or better is possible, which seems to be the average of most non-K overclocks


Copyright © PC & Tech Authority, nextmedia Pty Ltd Copyright © Alphr, Dennis Publishing

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