Locked Intel Core i5-12400 Gets Overclocked To 5.2GHz For A Huge Gain In Performance

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Once upon a time, there were two ways to overclock a CPU. Raising the multiplier has been the simplest and easiest option since it came to be, but old hardware nerds like this author will recall the days of raising motherboard front-side bus (FSB) clocks to accelerate memory accesses, as well as goosing the CPU clock rate. That technique more-or-less went away when processors integrated their "FSB" on-die, although modern "base clock OC" has made its return once before, during the Skylake era.

As it happens, that old technique of bus clock-based overclocking has come around once again, this time for Intel's latest 12th-generation Core processors (Alder Lake). Famed overclocker Der8auer was fooling around with a Core i5-12400 slotted into his ASUS ROG Maximus Z690 Apex board when he spotted an option that wasn't there before: "Unlock BCLK OC."

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Toggling that option allows the motherboard to scale the base clock to the sky. Using his Core i5-12400 sample, Der8auer was able to raise the BCLK to 131MHz, increasing the all-core clock rate on his Core i5-12400 to slightly above 5.2GHz. That gives him a six-core, twelve-thread processor based on Intel's latest Golden Cove CPU architecture running at the same clock rate on every core as the company's flagship Core i9-12900K CPU will hit on just a single core.

We knew something like this would show up; Intel bragged about it at its initial Alder Lake launch. However, BCLK OC options were either absent or much more limited using K-series CPUs. Der8auer notes that no one had been talking about BCLK OC on Alder Lake to this point because when a K-series CPU is installed, the motherboards simply don't present the options.

Image: Intel (click to enlarge)

For any confused novices in the audience, let us explain. Your microprocessor's clock rate is derived by applying a multiplier to a "base clock." For more than a decade, that "base clock" has been 100 MHz. On the Core i5-12400, the maximum multiplier that you can set manually is 40x. The extra 400MHz from Turbo can only be applied to a single core. Since you can't raise the multiplier any further, the only way to overclock these CPUs is to raise that base block.

That's actually been the case for Intel's desktop CPUs as long as it's been using "Core i" nomenclature, but for the most part, you couldn't move the base clock more than a couple of MHz without making the whole system unstable. With Alder Lake, Intel has decoupled the base clock from the rest of the machine so that you can adjust it without affecting anything other than the CPU, its memory, and the ring bus inside the CPU.

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There are a couple of catches, though. For one, even though you're only affecting the cache and memory speed with your BCLK-adjusting shenanigans, you do still have to be mindful of them. Eager overclockers making use of this method will need to be absolutely certain that they take stock of what values are being modified when they manipulate the base clock; it's all too easy to ramp up the base clock and end up having to reset your CMOS settings because you've made your machine unbootable.

The other big catch is that the option to unlock the BCLK is only present on a few motherboards that Der8auer has tested. He posted a second video today where he got some feedback from the community and confirmed that only motherboards that come with an external clock generator are capable of this kind of overclocking. So far, it seems like that list is limited to top-end enthusiast mainboards that cost multiple hundreds of dollars, which makes the prospect of slapping a cheap CPU in them to overclock sort of silly.

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Still, the performance gains are impossible to deny. In games and benchmarks that are heavily reliant on CPU performance, the overclocked Core i5-12400 meets or exceeds the performance of a Core i9-12900K despite costing just one-third as much.

Of course, even a 30% overclock won't make up for having less than half the cores, and in multi-threaded workloads—including PUBG—the little Core i5 stands no chance. It holds its own, though, and matches or beats an eight-core Ryzen 7 5800X even in multi-threaded work.

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Curiously, Der8auer attempted the same trick on a Core i5-12600, and while he was successful, it did not achieve the same overclock, which means the final performance was lower as the two processors only differ in clock rate. In the aforementioned follow-up video posted today, Der8auer overclocks a quad-core Alder Lake Core i3 processor, as well as a dual-core Celeron. Head over to YouTube to see his results.