If you often wonder why your CPU never seems to achieve the boost clocks it's advertised for, its power limits might be the reason. The way your motherboard manufacturer tunes the BIOS can hold your CPU back, even if you have a capable cooling solution on your PC. Your CPU has multiple power limits that work in tandem to determine the boundary conditions within which it operates. You can often tweak these limits in the BIOS/UEFI, changing your processor's behavior. However, you need to understand how they function before you can do that.
PL1 and PL2 govern your CPU's real-world performance
Behind the scenes of Turbo Boost
The most important power limits for Intel CPUs are PL1 and PL2. While PL1 is the sustained or average power that the CPU is set to draw over time, PL2 is the turbo power that the CPU can draw for short bursts. It is often recommended to set PL1 to the official TDP of the processor to allow for comfortable sustained operation. Another variable, Tau, denotes the amount of time your CPU will stay at the power level set by PL2, falling back to the PL1 limit once that time period expires. These three variables together govern the Intel Turbo Boost algorithms.
AMD also has similar power limits, but denotes them with different names. PPT (Package Power Tracking), TDC (Thermal Design Current), and EDC (Electrical Design Current) are the AMD equivalents, with PPT standing in for PL1, and EDC being similar to PL2, although it's a current limit rather than a power limit. Users can tweak these power limits for Intel or AMD processors using the BIOS/UEFI, Ryzen Master, and Intel Extreme Tuning Utility (XTU).
PL3 and PL4 are additional safeguards
Accounting for short-lived spikes
PL1 and PL2 aren't the only power limits on Intel CPUs; PL3 and PL4 are optional power limits that are usually locked, but can be changed by the user. PL3 and PL4 are additional limits that account for even shorter bursts of power. PL3 is an even higher power limit than PL2, which, if achieved, throttles the frequency to bring down the power supplied to the socket. On the other hand, PL4 is a limit that is never exceeded — think of it as the ultimate power limit that preemptively limits the frequency to prevent the CPU from reaching it.
For most users, configuring PL1 and PL2 is enough to tune their CPU's power levels to their liking. If your system can handle the elevated power levels and temperatures, then these two limits are enough to extract most of the performance from your CPU. PL3 and PL4 are additional safeguards that most of you don't ever need to touch.
Motherboard vendors often ignore these limits
The wild west
CPU manufacturers like Intel and AMD configure the power limits for each of their processors, but motherboard manufacturers aren't usually bound by the same rules. To boost CPU power and performance even further, and gain marketing mileage, they often configure the BIOS to exceed the manufacturer's limits. Often, motherboard vendors will set both PL1 and PL2 to unlimited, allowing processors to boost as high as the cooling system allows. This is clearly out-of-spec behavior, and can often lead to unintended consequences.
Your CPU will likely throttle after hitting the temperature limit long before delivering any meaningful gains in performance. Most CPUs have a TJMax of around 100℃, and they'll aggressively reduce the frequency before the chip can break any power level records you're dreaming of. Pushing high-end chips beyond what the manufacturer recommends opens the doors to system instability and a reduced CPU lifespan.
Different workloads respond to power limits differently
Higher power levels might not translate into desired results
It's great that you can modify your CPU's power limits, but not everything you do on your PC will benefit equally from more power. For example, gaming doesn't really push your CPU to sustained PL1 levels. PL2, on the other hand, might benefit gaming performance due to the short power bursts it allows. For productivity workloads like video editing and 3D rendering that love all the power they can get, the PL1 setting will have a bigger impact. Also, if you're chasing higher benchmark numbers, a higher PL1 might be worth exploring.
Your cooling solution will often be the limiting factor
The trade-off might not be worth it for most users
Despite the values you enter in the PL1 and PL2 fields in the BIOS, your PC's cooling chops will ultimately decide how far you can push your CPU. As you're not just playing with power limits but temperature limits as well, a high-end cooling solution is needed to keep the chip cool enough that it can keep striving for the power levels you've set in the BIOS. Even if you know that you can squeeze a few more frames out of an elevated power limit, the thermal overhead might not be worth the slight performance benefits.
Most users should undervolt their CPUs instead of overclocking or "overpowering". The lower voltage levels often unlock more thermal headroom for your CPU to automatically boost higher and deliver more performance. The default PL1 and PL2 values work best for most people who use their PC for gaming and occasional productivity. Enthusiasts need to invest in high-end cooling solutions if they want to push PL1 and PL2 higher and experience related performance benefits.
Understanding CPU power limits is essential for enthusiasts
While most users seldom need to touch their CPU's PL1 and PL2 values, enthusiasts who crave every last bit of performance need to dive deep into them. Modifying your CPU's power limits can improve performance significantly in certain workloads, provided you have the cooling capabiltiies to keep your CPU cool enough to avoid thermal throttling.