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The Coffee Lake Overclocking Guide (Page 3)

By Steven Bassiri from Jan 17, 2018 @ 11:00 CST

CPU Multipliers

There are a few multipliers you need to set when you overclock the CPU. You have multiple settings including CPU core, AVX offset, FCLK, and Cache/Uncore multipliers. While many vendors deviate from Intel's official setting names, we have gone ahead and provided what each setting is called in different UEFIs. All multipliers are multiplied by the base clock (BCLK) to attain a final operating frequency. By default the BCLK is 100MHz, but you can also increase BCLK to overclock the CPU, but you should recognize that increasing the BCLK will increase CPU, cache, FCLK, and memory speeds at the same time.


However, before we begin a few vendors have a setting that allows you to overclock all cores to maximum Turbo frequency (4.4Ghz on 8700K) instead of Intel's specification where cores are staggered between base and maximum frequency. The feature is called MultiCore Enhancement, and is a simple and easy way to overclock without having to mess with many settings. It is an easy way out, but you don't need to mess with it when you are overclocking manually.


Some vendors allow you to choose the core setting mode, such as the ability to sync all cores or set the cores individually. Start with 48x or 49x; I prefer using the sync all cores setting if there is one. On the SuperMicro motherboard, you can set core six setting to what you want the rest of the cores to be at if you don't want to set each core individually. On ASUS, the board will auto-change to sync all cores if you set XMP to enable as it's enabling multi-core enhancement all the way.


While most games and other software don't use Intel's AVX instruction set, many stability testing programs and some software programs do. AVX uses parts of the CPU typically not used and as such will greatly increase power consumption, temperatures, and it could require more voltage to remain stable.

Intel has added in an AVX Offset setting, which allows you to set a number of multipliers for the CPU core to drop down to if AVX is engaged. For example, if you set 50x for the Core ratio and -2 or 2 for the AVX offset, you will get a 5GHz overclock while playing games (no AVX) and 4.8GHz when running HandBrake (AVX). MSI lets you set a frequency for the CPU to shift to instead of a number of multipliers to go down when AVX is enabled.


The CPU cache, ring, and uncore all change the same setting in the CPU. The ratio mainly changes the cache speed, and some vendors have this turned up to 4.4GHz by default. While you won't be able to match the CPU core multiplier most of the time, you should be able to stay 4-6 multipliers below the CPU core multiplier without requiring too much extra voltage.

I would start with 4.2-4.4GHz cache ratio, overclock the CPU up to it's maximum and then go back and find a cache multiplier that doesn't require more VCore to stay stable. I should mention that VCore also provides power to the cache region and isn't a separate voltage rail like it was in the past. Some vendors allow you to set a minimum and maximum ratio for the cache, I typically just set them the same, but you can set a range if you like.


VCore is your main voltage for stabilizing the CPU core and cache overclocks. Every vendor offers the ability to set the VCore to override mode, and it's the default on a few brands (like GIGABYTE)., otherwise you have to choose. There are two other modes on most motherboards; adaptive and offset.

If you run your CPU at maximum speed all the time, then override is what you want, but if you are going to let the CPU multiplier go up and down according to load, then you will want to set adaptive or offset mode. I will go over CPU multiplier dropping on the next page. The adaptive mode allows you to set a VCore you want as maximum and will drop down the VCore if the multiplier drops.

The offset mode allows you to set some millivolts to be added or subtracted to the CPU's default VCore for each multiplier. The new CPUs have different VCore levels for each multiplier (called VID), and every CPU has its individual default voltage levels. By default, Intel specification requires the VCore to drop by a certain amount when load and multiplier are increased.

Load Line Calibration (LLC) reduces or reverses this default voltage drop, and it helps a lot when you are trying to stabilize the CPU. If you want to set offset on a GIGABYTE motherboard, you need to type "normal" to unlock offset mode (offset is called DVID in their UEFI). Many motherboards will auto increase VCore beyond Intel specifications based on "auto-rules", so it's best to always set VCore, try 1.28-1.3v when at around 4.9GHz.


By default, motherboards should set FCLK to a multiplier of x8 (800MHz), but many vendors have set 1GHz by default. If your motherboard has it set at x8/800MHz, you should go and increase it to 1x or 1GHz, as it could help GPU performance slightly. FCLK typically doesn't produce instability when increased.

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