What is CPU Throttling? – Thermal Throttling

If you are remotely into CPUs, or even into overclocking, you may have heard of a term called “CPU throttling”. What is CPU throttling and why should you care?

Basically, CPU throttling is the means through which a CPU controls its clock speed and voltage either automatically depending on the workload or due to the heat generated. It can also be affected by user assigned limits on current, voltage or power.

Automatic CPU throttling is also know as dynamic voltage and frequency scaling (DVFS) and is found on almost all modern CPUs. This technique of controlling clock speed is particularly useful among laptops and mobile devices where controlling heat and conserving power is essential.

Hence CPU throttling is a bigger concern on laptops as supposed to on desktops.

What is the CPU Base and CPU Turbo Boost Frequency?

Before you attempt to understand what is CPU throttling, it is important to first understand the base and the boost frequency of a CPU.

Base Frequency is the minimum clock speed that the CPU is designed to work at. 

Turbo Boost Frequency is the maximum clock speed the CPU is designed to work at (if NOT overclocked).

In throttling, these two numbers are often quoted.

In ideal conditions, the CPU automatically throttles between the base and boost frequency. This is desirable.

However, if the throttling is caused by an issue, you may not see the CPU hitting the boost or even the base frequency levels. 

Different CPU types have different base and boost frequencies.

For instance high performance CPUs have a higher base and boost frequency. Power saving CPUs have a lower base and boost frequency.

The following table compares the 11th gen Core i7 models based on their base and boost frequency

CPU Base Boost TDP (W) Remarks
Intel Core i7
3.60 GHz 5.00 GHz 125 Desktop Grade High performance 
8 Core / 16 Threads
Intel Core i7
2.50 GHz 4.8 GHz 45 Laptop Grade High Performance
8 Core / 16 Threads
Intel Core i7
2.80 GHz 4.7 GHz 28 Laptop Grade Power Saving 
4 Cores / 8 Threads

You can see that laptop grade CPU often have lower base and boost frequencies. 

Another very important point to note is the TDP.

What is TDP in Brief?

In order to understand what is CPU throttling, you must also get some grasp of what TDP is.

TDP stands for Thermal Design Power and it is expressed in Watts. Intel defines this as a the maximum power consumed when the CPU is operating at base frequency with all cores working.

Here are the points to note with regards to TDP as it is central to the theme of CPU Throttling:

  • The higher the amount of cores, the higher is the TDP of a given CPU
  • The higher the frequency, the higher the TDP of a given CPU.
  • The higher the TDP, the more heat the CPU generates.
  • The more heat the CPU generates, the higher are the chances of throttling if adequate cooling is not provided.

What is CPU Throttling?

As mentioned earlier, CPU throttling is the technique through which CPU controls voltage and frequency.

In ideal cases, it can also be called the process through which the CPU varies the clockspeed between base and boost frequency.

However, there are also less than ideal causes which can throttle a CPU.

CPU throttling is generally done automatically and depends on the following situations:

  1. Running on Battery Or Not
  2. Depending Upon Your Workload
  3. Heat Generation – Thermal Throttling

1. CPU Throttling When Running on Battery

This is quite obvious to note and is common among CPUs.

Laptops CPUs are designed to throttle down when running on battery in order to conserve power.

Take for instance my laptop CPU i.e Intel Core i7 7700HQ. This has a base frequency of 2.80 GHz and a boost frequency of 3.80 GHz.

When running on battery, the operating frequency is very close to the base frequency:

CPU throttling power
CPU Throttling when running on battery

When running on power, you can see that the operating frequency increases, albeit still not touching the max turbo boost frequencies since the workload is light.

CPU throttling power power plugged in

2. CPU Throttling Depending Upon Your Workload

This bring us to the next point.

Depending upon the type of work being performed, the CPU can increase or decrease its frequencies (as well as the amount of cores being worked on).

You can monitor the clock speed and the utilization of cores through task manager.

3. Thermal CPU Throttling

What is CPU Thermal Throttling? Thermal Throttling is basically a fail-safe mechanism. It prevents your CPU from getting damaged due to heat.

Often when the cooling system of a PC fails or if you haven’t provided adequate cooling to your PC, then the CPU will do one of two things:

  1. Throttle or undervolt itself in order to reduce the clock speed and thus generate less heat
  2. Shut down when the temperature reaches critical temperature.

Also Read: What is the Safe Idle CPU Temperature?

Thermal Throttling and CPU TjMax Temperature

Throttling is the first attempt of the CPU to save itself as the temperature rises.

When the CPU reaches its TJmax or the Maximum Thermal Junction Temperature, it will start to slow down. This is usually at 100°  Celsius.

You can check the the TJMax temperature of your CPU using a simple free third party utility known as Core Temp.

Core Temp TJmax
TJMax temperature for Intel Core i7 7700HQ

This utility will not only tell you the TJMax temperature of your CPU, but will also let you monitor the nominal and the maximum temperature your CPU cores are registering.

In case if your CPU is registering a high temperature, or temperature close to the TJMax, then you need to consider a better cooling solution.

You should aim for the temperature to be in the 50°-60° C range when running nominally.

Tjunction max is the maximum thermal junction temperature that a processor will allow prior to using internal thermal control mechanisms to reduce power and limit temperature. Activation of the processor’s thermal control system may cause performance loss… – Intel

This is by far the most common issue faced by desktop DIY builder who fail to provide adequate cooling to their PC.

Also Read: How to Monitor CPU and GPU Temp While Gaming?

What Can Cause CPU Throttling?

There are many causes to CPU throttling , some of which I have covered above. 

Natural Causes

Some of the causes of the CPU throttling are built-in i.e the CPU lowers or increases its clock speed depending upon the workload or if it is being operated on battery.

Overclocking – Heat Generated

Often times overclocking your CPU when you haven’t provided adequate cooling can shoot up the temperature of the CPU resulting in throttling.

Also Read: How to Check if CPU is Overclocked?

Inadequate Cooling / Dirt / Not Enough Thermal Paste

Whether you have overclocked your CPU or not, if your CPU is not well ventilated, if the chassis has accumulated thick layers of dust preventing ventilation or if you haven’t applied adequate thermal paste between the CPU and the CPU cooling fan, then all this will lead to CPU throttling.

Also Read: Laptop CPU vs Desktop CPU

User Designated Limits

If you have undervolted your CPU or if you have deliberately set a lower Turbo Boost frequency for your CPU, then the CPU will naturally throttle based on your settings.

Undervolting generates less heat, but also prevents your CPU from reaching optimal clock speeds.

Thermal vs Power Limit vs Current Limit vs VRM Throttling

Thermal throttling, power limit throttling, current limit throttling and VRM Throttling are all different types of factors that can lead to CPU throttling.

Incidentally these are also the CPU throttling factors that Intel Extreme Tuning Utility (Intel XTU) makes mention of.

What is CPU Throttling
CPU Throttling Factors in Intel XTU

What is CPU Thermal Throttling?

As talked about earlier, thermal throttling happens when high CPU temperature leads to CPU throttling.

This can be due to poor ventilation or due to overclocking.

What is VRM Throttling?

motherboard vrms labelled box phase power design w
Motherboard VRMs

VRM, or voltage regulator modules, are the electrical devices that make sure your CPU gets clean and the right amount of voltage. 

The more powerful the VRMs and the more of them you have on the motherboard, the better voltage control you will have for the CPU, particularly when overclocking.

However, often, if you have weak VRMs, they can get overheated and thus throttle your CPU.

If you have recently overclocked your CPU but if it is giving you unsatisfactory result or negative results DESPITE your CPU temperatures in the green, then there are high chances that your VRMs are heating up.

In fact, VRMs heating up can result in drastic CPU throttling. 

Also Read: How is Processor Speed Measured?

What is Power Limit Throttling?

There are multiple reasons for Power Limit to throttle your CPU.

For starters, it can be due to user settings.

PL1 and PL2 Levels Set to Too Low

Intel makes mentions of two different powers that you can set for your CPU:

  • PL1: Power for for Turbo Boost Power Max (Ideally should match the TDP of your CPU)
  • PL2: Power Limit for Turbo Boost Short Power Max (Ideally should be higher than the TDP).

Power Limit Throttling Intel XTU 2

These two settings, along with the Turbo Boost Power Time Window settings, govern how much the CPU can turbo boost and for how long.

The Turbo Boost Short Power Max (PL2) essentially defines the maximum turbo boost frequency that the CPU is allowed to achieve.

The higher the PL2 rating, the higher the clockspeed the CPU can achieve (higher the power, higher the clockspeed).

Turbo Boost Power Time Window defines for how long the CPU is allowed to run at boost frequency.

There has to be a reasonable limit because running for along time on boost can give you opposite results. Why? because running on boost can overheat your CPU and the VRMs, thus resulting in Thermal and VRM throttling.

If you often experience Power Limit Throttling i.e if the Power Limit Throttling indicator in Intel XTU turn to “Yes” often, then you can experiment with PL1 and PL2 Power Levels.

However, make sure you have adequate cooling provided to avoid seeing negative results. 

Power Limit Throttling Due to Undervoltage

If you have deliberately set the maximum voltage of the CPU through BIOS or through a utility, then that would naturally lead to CPU throttling due to power limit.

Lower the voltage, lower is the clock speed and in turn, lower is the heat generated.

What is Current Limit Throttling?

Similar to Power Limit Throttling, Current Limit Throttling affects your CPU when the CPU wants to draw more current but:

  1. Your motherboard isn’t designed to supply the required current.
  2. The max current draw for the VRMs in the BIOS settings is set to low and thus does not allow the CPU to use more current than assigned.

If your systems keeps hitting the Current Limit throttle, try increasing the IccMax (supply current) or the VRM supply current from BIOS or from an overclocking utility like the Intel XTU.

Again, if adequate cooling is not provided for the CPU or the VRMs, you will see your system hitting Current Limit Throttle even if you set a higher IccMax current.

Also Read: What Should I set PCIe Frequency When Overclocking?

Final Words

So what is CPU Throttling? The concept of CPU throttling is analogous to the throttle in a car.

Just as the throttle in a car regulates the power through controlling the amount of air getting into the engine, the CPU throttle regulates the clockspeed based on the voltage, current and heat in the system.

In most cases you do not have to worry about this much as it is handled automatically. However, if you are an overclocker or if you are getting a lower than ideal clock speed on your PC, then you may want to look into it.

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Atif Qazi
Atif Qazi is the founder of PCGuide101. He is a digital nomad who loves everything PC. He is a PC builder, tech enthusiast, engineer, and a lover of single player lore-rich RPG games.

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