Clock Frequencies

The following chart shows how well the processor sustains its clock frequency, and which boost clock speeds are achieved at various thread counts. This test uses a custom-coded application that mimics real-life performance—it is not a stress test like Prime95. Modern processors change their clocking behavior depending on the type of load, which is why we provide three plots with classic floating point math, SSE SIMD code, and the modern AVX vector instructions. Each of the three test runs calculates the same result using the same algorithm, just with a different CPU instruction set.

Overclocking

Overclocking the Core i9-12900KS is quite complicated despite the unlocked multiplier. All "K" processors made by Intel have their multipliers unlocked, so you can just dial in the desired clock speed. The problem is not with the mechanics of overclocking, but with the challenge of somehow being able to manage the heat output.

That's why my approach was a bit different from the usual for the best overclock. For the 12900KS, I started with all cores set to the same x49 multiplier for 4.9 GHz all-core and increased the voltage until I got close to the thermal limit of 115°C when running Prime95. Unlike other Alder Lake processors, including the Core i9-12900K, the KS has its out-of-the-box default thermal limit set to 115°C, not 100°C. 115°C is the highest manual setting you can pick in the BIOS for all Alder Lake CPUs. Since this is the default setting, Intel's warranty will cover operating the processor at up to 115°C, which is a good hint for users of other Alder Lake processors based on the same silicon; there's no reason those can't withstand 115°C, too.

In terms of voltage, I settled for 1.35 V and started increasing the multipliers until the system got unstable. Increasing the clocks increased the heat output, so I had to dial down the voltage a little bit—the idea here is to pump as much (or little) voltage into the CPU as the cooling solution can handle as heat. At that voltage, I was able to run at 5.3 GHz almost stable, so I settled for 5.2 GHz all-core for our OC testing. Since 5.2 GHz was rock-stable immediately, there was a little bit of headroom to reduce the voltages further, which brought down power and heat a bit. If you have a high-end custom water-cooler, I'm sure you could easily go to 1.4 V and above to reach 5.4 GHz all-core or more.

This is a significant improvement over the i9-12900K, where I maxed out at 5.0 GHz—seems the new KS is better-binned indeed.