FLL OC Mode is a function present on Alder Lake and Raptor Lake CPUs which enables high frequency overclocking since microcode 0x12.

FLL stands for Frequency Locked Loop. I’m not an electrical engineer, so I won’t be able to explain how it works from a technical perspective. Therefore, let me just focus on the practical stuff.

As I wrote in my Alder Lake launch article, leading up to the Alder Lake product launch there were some issues with extreme overclocking. This is not uncommon as pretty much every platform requires less or more work to enable extreme overclocking. One of the issues that popped up was a PLL-related bug that caused the CPU frequency to report much higher frequencies than it was actually running. Even much higher than 10 GHz!

The FLL OC option fixes this specific issue with extreme overclocking. There are 4 settings

• No overclocking (Disabled)
• Ratio overclocking with nominal BCLK (Normal)
• Moderate BCLK overclocking between 100 and 300 MHz (Elevated)
• Extreme BCLK overclocking between 300 and 500 MHz (Extreme Elevated)

For extreme overclocking aficionados who look forward to the maximum CPU frequency on Alder Lake and Raptor Lake, I believe CPU-Z should already have the FLL OC mode check in place to ensure the overclocking records validated on the website show the correct frequency. This should be the case from CPU-Z v1.98.

For regular or daily overclocking, FLL OC mode has little impact so it is not necessary to configure this option. You can let the motherboard configure it automatically with its auto-rules.