Why do CPU's get hot?

Posted by Thomas Ducpham on May 11th 2018

Why do CPU's get hot?

One of the few enemies to any computer hobbyist, heat can be attributed to countless computer failures. Often times when a computer overheats, it’s the result of negligence.

Let's explore where this heat is coming from and why our computers are so susceptible to this.

Understanding Transistors (on CPUs and other Electronic components)

Transistors can be found on a CPU which does most of the calculations in computing. Every transistor has components in them to either allow electricity to flow through it, or block it. When electricity is blocked, this was referred to in binary as “off or 0” and “on or 1” when it isn’t blocked. This exact concept can be further explained by examining a light switch. We’re purposely blocking electricity to a light when the switch is turned off, but not when we flip the switch on.

There isn’t much heat generated from allowing electricity to flow through something (unless there is A LOT of electricity) but trying to stop the flow on the other hand does. It’s like the Hoover Dam stopping the flow of the Colorado River. If you were able to instantly place and remove the dam, the clash of water would generate a destructive force.

But, It’s not just one transistor that generates a lot of heat.

SOURCE:HACKADAY (https://hackaday.com/2018/01/20/vacuum-tubes-shipping-through-ebay-now-challenging/)

Because Intel’s CPUs can have up to 100 Million Transistors per square millimeter.

That’s not exaggerating either. Early transistors were big enough to hold in your hands, sometimes referred to as “Vacuum Tubes”. Computer’s actually think in ones and zeros, so the more transistors you have, the better the computer can solve problems.

But heat is a problem when you have literally millions of transistors scrunched together..

We’re combating heat by using heat spreaders, and heat sinks

Or, pieces of metal with thin gaps that extended from top to bottom usually planted on top of heat generating devices. It works by having a fan on top of the heatsink, cooling the metal fins. By law of thermodynamics when two objects are in contact of each other, they transfer heat. So, the more the fans can remove the hot air around the gaps, the cooler an object can run.

Extra Heat

Can also be a problem if left unchecked. For example, if you have poor ventilation like a blanket of dust inside your computer, it can effectively keep heat inside -- not allowing hot air to be replaced by cooler air. Dust is usually the number one reason why temperatures climb quickly, so it is advisable to clear out vent holes and crevices that are dirty. To further promote better airflow, case manufacturers are starting to building bracket mounts for wires inside of a computer. This would allow mounting wires behind a motherboard, rather then leaving them dangling in the front.

Believe it or not, but a wall of wires can pose as another huge problem in heat dissipation!

You can also get extra heat from tweaking CPU settings

Understanding Overclocking

A CPU can also heat up quickly by pushing it beyond its factory specifications. Telling the CPU to operate at 150% speed for example, increasing how fast the transistors work usually requires a much better cooling system. While true you can use a liquid based system to combat the extra heat generated by overclocking (like what you find in cars), you theoretically can keep your computer in an overclocked state as long as the components on the CPU never reach a critical temperature. Overclocking is a bit more than telling your CPU to run 150% faster, but also giving it more electricity/voltage than recommended. As stated earlier, the more “water” you are having the dam hold back, the more energy is produced when you stop it. It’s very possible to burn out your CPU entirely without proper research on how far can you really push things.


The CPU isn’t the only thing responsible for heat generation, there are other things to consider like your hard drive ( which depending on what kind you are using, can generate mechanical energy) or a graphics card. As computers get more and more advanced, we will eventually have to rethink how we approach this topic as a whole.