There are a lot of different fan headers on modern motherboards, and all of them serve different purposes. The CPU fan header and the SYS fan header are the most common. But what is the difference between the CPU and the system fan?

The main difference between CPU and SYS fans is their purpose. A CPU fan is used to cool down the central processing unit of your computer and is mounted on top of the CPU itself. On the other hand, an SYS fan is used to cool down other components in your system and is placed on your PC case.

If you want to know more about the different kinds of headers found on a motherboard, the differences between them, and what they’re used for, keep reading as I will go into more detail about the different headers and how to use them.

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Let’s start from the basics and explain what a motherboard header is for those who may not know. A motherboard header is simply a connector on the motherboard that allows you to connect a device. In most cases, headers are used to connect fans and LEDs, but they can also be used for other things like USB hubs, SATA controllers, and more.

The most common headers you’ll find on a motherboard are:

In this article, I will only be talking about fan headers since that is the main topic, but it’s important to know that there are other types of headers as well.

Related Article: What are USB headers?

A fan header is a connector on the motherboard that allows you to connect a fan. There are different kinds of fan headers, but the most common ones are 3-pin and 4-pin fan headers.

So let’s talk about the differences between a CPU fan header and a system fan header.

As already mentioned, a CPU fan header is used to connect a cooling fan to your CPU, and the fan is mounted on top of the CPU itself. On the other hand, an SYS fan header is used to cool your entire system, and the fan is usually mounted on the back and front of your PC case.

But to better understand the difference, let’s take a look at the different types of fan headers.

The system fan headers labeled as SYS_FANS are used to connect your computer case fans to the motherboard. They are the most common fan headers and are either 3-pin or 4-pin. The amperage of both 3-pin and 4-pin SYS fan headers is usually 1A or below.

The majority of motherboards have multiple SYS fan headers (2-5) so that you can connect all the fans in your computer case.

The difference between 3-pin and 4-pin fan headers is that a 4-pin header has an extra pin that allows the motherboard to control the fan’s speed. A 3-pin header does not have this capability, and the fan will run at full speed all the time.

The 3-pin SYS fan header is the most common type of fan header you’ll find on a motherboard and is used for DC fans. DC Fans are the most common type of fan used in computer cases; they are pretty old technology and are not very efficient. They only have three pins and do not support speed control; this means that the fan will always run at full speed.

The 4-pin SYS fan header is very similar to the 3-pin header but has an extra pin that allows the motherboard to control the fan’s speed. This is an excellent feature if you want your computer to be quiet and only have the fan running at full speed when needed.

The 4-pin headers are used for PWR (Pulse Width Modulation) fans, a newer and more efficient type of fan.

The difference between a PWR fan and a DC fan is that a PWR fan can have its speed controlled by the motherboard, which means it can run at a slower rate when not needed and only ramp up to full speed when required. This makes PWR fans much more efficient than DC fans.

The amperage of a system fan header is significant because it’s what controls how much power the fan can draw from the motherboard. As I mentioned earlier, the amperage of both 3-pin and 4-pin SYS fan headers is usually 1A or below.

This should only concern you if you plan to use a Y-splitter to connect multiple fans to one header. In this case, you need to make sure that the combined amperage of all the fans does not exceed the amperage limit of the header.

For example, if you have two 0.5A fans and want to connect them to a 1A header, that’s no problem. But if you have two 1A fans and you want to connect them to a 1A header, that’s going to be a problem because the combined amperage of the two fans is 2A which exceeds the 1A limit of the header.

A sys fan is typically a large, flat cooling fan mounted on the back or front of a computer case. Sys fans come in various sizes and shapes, but the most common size is 120mm. Other sizes include 80mm, 92mm, and 140mm.

Related Article: How To Connect Extra Fans To Motherboard

The CPU fan header labeled as CPU_FAN is used to connect a cooling fan to your CPU. The fan is mounted on top of the CPU itself. It is a 4-pin header and, like other fan headers, has an amperage rate of 1A.

There is only one CPU fan header on most motherboards, usually located near the CPU socket.

The CPU fan header is essential because the CPU produces a lot of heat and needs to be adequately cooled to function properly. If the CPU fan is not connected correctly to the header, your computer will not boot.

A CPU fan typically looks like a large, thick cooling fan mounted on top of the CPU itself.

The power supply fan header, labeled as the PWR_FAN, is a very common header used to connect your power supply’s fan to the motherboard for monitoring purposes. Not all Power supply units have a cable to connect to this header, but most do.

The power fan header can also be used for sys fans, but keep in mind that it does not support the speed control feature. This means that the fan will always run at full speed. The power fan header is either a 3-pin or 4-pin header and has an amperage rate of 1A.

Before wrapping up, I want to quickly mention the CPU optional fan header. This header is not present on all motherboards and can be found only on high-end models.

The CPU optional fan header labeled as CPU_OPT is used to connect a second cooling fan to your CPU. This is useful if you have a very powerful CPU that produces a lot of heat and needs extra cooling.

The CPU optional fan header is a 4-pin header and has an amperage rate of 1A.

Yes, you can plug a sys fan into the CPU fan header. If you don’t have any free sys fan headers, you can use the CPU fan header using a Y-splitter. But this is not something we recommend because it’s not ideal for cooling.

The difference between a 3-pin and a 4-pin fan is that a 4-pin fan can have its speed controlled by the motherboard, which means it can run at a slower pace when not needed and only ramp up to full speed when necessary. A 3-pin fan cannot have its speed controlled by the motherboard and will always run at full speed.

Yes, you can plug a 4-pin fan into a 3-pin header, but you won’t be able to take advantage of the fan’s speed control feature. The fan will run at full speed all the time.

Yes, you can use a 3-pin fan on a 4-pin header. The fourth pin is for speed control and won’t be used by 3-pin fans.

SYS fan is short for system fan. A sys fan is a cooling fan used to cool down the inside of your computer. Sys fans come in various sizes and shapes, but the most common size is 120mm. Other sizes include 80mm, 92mm, and 140mm.

In conclusion, the difference between CPU fans and system fans is that CPU fans are used to cool down your CPU while system fans are used to cool down the inside of your computer. Both fans are essential for keeping your computer running correctly and preventing overheating.

Make sure to connect both fans to their respective headers on the motherboard to keep everything running smoothly. Thanks for reading, and feel free to leave any questions in the comments section below.

Nick Ryley is a computer architect and the owner of The Pc Geekz. His love for playing games got him interested in computers in the first place. He wanted to be able to build a gaming PC that could run all the latest games at max settings, and this has him pursuing a major in computer architecture! He started this blog to help people out and answer some of the most common questions about computer building