What Is CSM Boot in Windows 10 and How to Enable or Disable it

Scenario: What is CSM boot mode and do I need it enabled?

"Can anyone please explain what is CSM setting is in BIOS and do I need to have it enabled or disabled? I installed my Windows 10x64 in UEFI mode. But, in the BIOS CSM support is still activated. Can I deactivate it afterward in order to get a faster boot, among other things?"

About CSM in BIOS

CSM means “Compatibility Support Module” which is a sub-item in the Boot option in BIOS, and it appears on the later motherboard, the previous one doesn’t have this option. CSM is a parallel item with Secure Boot.

Through CSM, UEFI firmware implementations on PC-class machines can also support booting in legacy BIOS mode from MBR disks, because CSM provides compatibility for the Legacy systems. And CSM will make the booting in the same manner as on traditional BIOS-based systems, by disregarding the partition table and relying on the content of a boot sector.

To put it in a nutshell, CSM exists to provide compatibility with systems that support or do not support UEFI completely, as well as systems that must be installed in Legacy. Therefore, if you need to boot a traditional MBR device, you need to enable the CSM.

On some devices with later operating systems that need GPT + UEFI mode, the CSM option is disabled by default and the Secure Boot option is enabled. In this situation, if you want to use some systems that need MBR + BIOS mode, you’ll have to enter the BIOS board to close Secure Boot and enable CSM.

For example, some people might need to install Windows 7 in UEFI mode. Since the Windows 7 system cannot fully support UEFI, if a computer that supports UEFI wants to install and use Windows 7 in UEFI mode, the CSM function must be enabled.

How to enable/disable CSM in Windows 10?

Although newer mainstream machines and systems now support UEFI, they may still be installed in MBR + Legacy mode which only supports this mode, while the CSM option must be enabled. But, how do enable or disable CSM when it’s necessary? Well, it’s not complex.

As we mentioned above, CSM is a sub-item in BIOS, so you can enter BIOS to adjust it. But, there’s one thing you might take into consideration. That is the boot disk you’re going to execute operations. You need to match your boot disk perfectly with BIOS mode and UEFI mode, GPT for UEFI mode, and MBR for BIOS mode, otherwise, your computer will tell you “No operating system found”.

Now let’s see how to enable or disable CSM:

Step 1. Press the specific key to enter BIOS and then you might need to find where CSM is. Normally, it’s in advanced settings or Boot settings. It’s different in various motherboards.

Step 2. Find and Select the CSM, click it, and then you can choose to enable it or disable it.

If you choose to enable it, then you need to check the Secure Boot option to make sure it’s disabled.

After you change the settings, please make sure your boot device is in GPT partition mode, if it’s MBR, you’ll need to convert it to GPT. Otherwise, your OS won’t be detected when you restart, so we suggest you convert the disk first before you enter BIOS to adjust your settings.

Convert to MBR to enable CSM boot in Windows 10

You can easily find how to convert data disks in Disk Management and CMD. Or you can choose MBR2GPT if you're using Windows 10 1703 or later systems. Of course, you can use them to finish this job. But, the first two will erase data, and the second only works on the system disk. Thus, if you don’t want to lose data or reinstall your system, then you can try this tool: AOMEI Partition Assistant Professional.

This tool can convert both data disk and system disk without losing data or reinstalling the system, and the operations are user-friendly for everyone. Users can flexibly change partition style from MBR to GPT or GPT to MBR. If you’ve tried Disk Management you might find that the convert button is greyed out, but AOMEI Partition Assistant can be the “Plan B” to assist you.

Step 1. Right-click the MBR disk you want to convert and choose “Convert to GPT”. If the selected disk is a GPT disk, then the option will be “Convert to MBR”.

Step 2. You'll be asked that "are you sure to convert the selected disk from MBR to GPT disk?", click “OK”.

Step 3. To commit the operation, please click “Apply”.

It’s quite simple, right? Now you don’t need to worry about your device can’t detect your system.

Ending words

You need to judge whether your device needs CSM boot in Windows 10 or not according to the actual situation because it will slow down the speed of system self-check. AOMEI Partition Assistant is a versatile software that also allows users to move installed programs, clone disk or partition, migrate OS…, etc.