What to set?
I have also taken Intel's recommended voltages for the Skylake CPU from their 6th Generation Datasheet (highlighted in blue) and added my recommended voltage ranges (in green) from experience (and looking at auto rules on motherboards). You are welcome to follow Intel's specifications, but for VCore, I don't recommend running over 1.5v even though Intel supports up to 1.52v, and I do recommend running the VCCSA/VCCIO/DRAM a bit higher for higher speed kits.
Serial Voltage Identification "SVID": A few generations back, Intel introduced serial voltage identification (SVID) which is a protocol the CPU uses to communicate with the voltage regulator. The power control unit inside the CPU uses SVID to communicate with the PWM controller that controls the voltage regulator. This allows the CPU to pick its optimum voltage depending on current conditions (temperature, frequency, load, etc.). You can actually use a combination of SVID and LLC to get an optimal VCore instead of manually setting it. If you start your system without making any changes, your VID (which some refer to as the stock voltage) might be 1.25v, but if you lower your CPU multiplier and restart, you will find your VID has dropped automatically. The reverse happens if you increase your clock and do not set any VCore. Intel's latest CPUs are able to pick their own voltage, and this comes into play if you want to utilize "offset" / "adaptive" voltage. The good news is that if you come from Haswell, you should look forward to a CPU that has the same or better durability.
UEFI "Auto Rules": Many motherboard manufacturers want you to overclock as far as possible; it helps with customer satisfaction as well as manufacturer reputation to support higher clocks. Since they know many users do not know how to overclock, they make things a bit easier by implementing "auto rules". These rules are pre-set voltages, timings, and even frequencies which are higher than stock, which are applied when you have the settings at "Auto" and a trigger is activated (example: you set 4GHz memory speed and leave VCCSA, VCCIO, and DRAM voltages on "Auto"). The CPU also does this on its own through SVID with the different VID for each frequency.
Motherboard manufacturers can override this with their own core voltage for a set multiplier, but this is not as common as it once was. Auto rules for DRAM overclocking are much more common. If you set XMP or set a high DRAM multiplier, and you keep track of the VCCSA and VCCIO, you will notice they rise, sometimes more than needed. On many boards, setting close to 4GHz DRAM frequency with or without XMP will trigger an auto-rule that pushes VCCIO and VCCSA upwards of 1.2-1.35v. Be aware that if you do not set a voltage, and that voltage is set to "Auto" then you are basically letting the board makers set what they feel is safe and stable.
I have not heard of any issues with CPU life or degradation because of this, but I do hear some people say, "well this board OCes this better", and many times it's because of auto rules or a lack of them (believe me, I have tested over 20 Z170 motherboards, some apply heavy LLC). Some UEFIs allow you to avoid "auto-rules" by setting the voltage labels to "normal". Normal is the Intel stock voltage. To totally avoid auto rules, you can either manually set things or set normal, but most of the time you will be okay with "auto-rules".
I have gone into the UEFI/BIOS of each of the five boards used in the guide so far and found the equivalent voltage labels. Like multiplier labels, the voltage labels also differ but control the same rails. Intel has combined the Core and Cache voltage rails, which is labeled as VCore or Core voltage in many UEFIs. Some boards offer different voltage operation modes for VCore covered below. I will cover power savings later in this guide, but power savings can allow for the drop of frequency and VCore. There are three major voltage modes present in the UEFIs of the different boards; Manual/Override, Offset, and Adaptive. In some UEFIs, you can either set a VCore, or you are required to choose the VCore mode (Manual/Override, Offset, and/or Adaptive).
Manual/Override Mode: This mode will override CPU power savings by disallowing voltage drop during idle and apply the voltage you type in (of course the VCore will drop depending on LLC settings covered later on). This mode of operation is what is always used for extreme overclocking since the core speed is always 100%. This mode is simple to setup. There is one caveat; the VCore does not drop if the CPU frequency drops. If you do want the CPU voltage to drop when the CPU is at a lower clock speed, then you need to use Offset or Adaptive mode.
Offset Mode: Offset utilizes the CPU's own self-VCore mechanism (like SVID or DVID) and then adds or subtracts a voltage level you choose. Offset mode is quite popular among those who want to let voltage drop along with CPU frequency, but because of Skylake's ability to change its VCore on-the-fly, you need to test exactly what the base CPU voltage is at your max frequency. Once you find that base voltage, you can determine the correct offset. Be aware that LLC also might play a negative role in offset overclocking, it can add too much to the offset during load or too little during idle, you need to test the VCore at idle and at load and possibly utilize a very low LLC level.
Adaptive Mode: Adaptive mode was introduced with Haswell because the integrated voltage regulator (FIVR) offered the CPU greater control of voltage over a large frequency range; it was much easier and much faster for the CPU to calculate how much voltage to apply at frequencies below the maximum set. Adaptive mode was basically an extension of the automatic CPU voltage mode and you could set a target voltage and/or an offset. Skylake doesn't offer exactly the same level of voltage regulation, so adaptive mode seems to have been implemented a bit differently (through SVID) and BIOS manipulation.
I tried it on multiple boards (three of the five in this guide have the option) and it seems broken on most of the boards. On the one board it works on there are some users who complain about it screwing up after recovering from sleep. Word on the street is that Intel's recent base UEFI firmware screwed up adaptive mode, and Intel has yet to implement a proper fix. If adaptive mode is not working for you and you want your CPU frequency and VCore to drop at idle, then I recommend you use offset mode or use SVID auto voltage with LLC levels (it's why some manufacturers provide so many LLC levels).
Load Line Calibration (LLC): During normal CPU operation, the CPU load will either go up or go down, and the auto CPU voltage goes in the opposite direction of the load. When the load is higher, current is also much higher, and staying at the same VCore would result in much higher power consumption since power is heavily dependent on voltage and current. To maintain the same power window and compensate for low quality VRMs, the VCore is dropped when current/load increases. LLC lessens, removes, or reverses the stock VCore behavior to increase stability. You can either set a higher VCore so that when it drops during load the CPU will still be stable, but you will reach a point where the low-load VCore is too high for comfort, and that is when you use LLC. LLC allows you to alter this voltage drop to increase stability without going too high at idle. For each board I have documented LLC at multiple levels in the motherboard section.
VCCIO, VCCSA, and DRAM Voltage: As I stated earlier, most motherboards have strong "auto rules" pertaining to these voltages. If you want to overclock your memory over 3GHz, you will probably have to tune these voltages, and I have outlined my results with 4GHz speeds on the next page. I recommend starting at 1.2v VCCIO and VCCSA and whatever DRAM voltage is written on your kit.
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- Page 1 [Introduction to Skylake Overclocking]
- Page 2 [Disclaimer and Before You Begin Overclocking]
- Page 3 [Overclocking Flow Chart, Non-K SKUs, BCLK, and Multipliers]
- Page 4 [BCLK, Core, Cache, Memory, and FCLK Scaling]
- Page 5 [Skylake Overclocking Voltages]
- Page 6 [Power Savings and Voltage/Power Analysis]
- Page 7 [The Durability of Intel's 14nm Node]
- Page 8 [Skylake Memory Overclocking: Corsair and Frequency Scaling]
- Page 9 [Skylake Memory Overclocking: G.Skill and Memory Timings]
- Page 10 [ASRock Z170 Overclocking: Z170 OC Formula]
- Page 11 [ASUS Z170 Overclocking: Maximus VIII Extreme]
- Page 12 [EVGA Z170 Overclocking: Z170 Classified 4-Way]
- Page 13 [GIGABYTE Z170 Overclocking: Z170X-SOC Force]
- Page 14 [MSI Z170 Overclocking: Z170A XPOWER GAMING TITANIUM EDITION]
- Page 15 [Stability Testing, Delidding, Crashing, and Throttling]
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