What is CSM and do I need it enabled?

[otec]

Hi,

Can anyone please explain what is CSM setting in BIOS and why do I need to have it enabled?

I'm running M.2 Samsung 950 as a boot driver with Windows 10.

Currently I don't use EFI boot partition, as I can't still figure out how to mark it as boot and rebuild bcd (when I reinstalled windows from old hard drive, I forgot to disable old EFI partition).


Thank you!

[Chino]

From Wikipedia:

Compatibility Support Module[edit]
The Compatibility Support Module (CSM) is a component of the UEFI firmware that provides legacy BIOS compatibility by emulating a BIOS environment, allowing legacy operating systems and some option ROMs that do not support UEFI to still be used.[48]

CSM also provides required legacy System Management Mode (SMM) functionality, called CompatibilitySmm, as an addition to features provided by the UEFI SMM. This is optional, and highly chipset and platform specific. An example of such a legacy SMM functionality is providing USB legacy support for keyboard and mouse, by emulating their classic PS/2 counterparts.[48]

[otec]

So, if its there for compatibility reasons, how come my Windows 10 boots from a non EFI m.2 drive without any problem with CSM is disabled?

[PerpetualCycle]

otec wrote:
So, if its there for compatibility reasons, how come my Windows 10 boots from a non EFI m.2 drive without any problem with CSM is disabled?

Mostly there for non-EFI devices (like video cards without EFI GOP drivers). Also it will need to be disabled if you want to do secure boot, which requires full EFI.

[Jimbo93]

otec wrote:
So, if its there for compatibility reasons, how come my Windows 10 boots from a non EFI m.2 drive without any problem with CSM is disabled?

There must be a EFI boot partition somewhere you didnt know was there. Look in the bios at the boot options and youll see it.

[Chino]

Some users disable CSM to decrease boot time.

[MNMadman]

Who says you need to have it enabled? Mine isn't.

It might need to be enabled for an operating system that doesn't have native NVMe drivers. Win10 does have native NVMe drivers, so CSM isn't needed.

And once you have the Samsung NVMe installed you can probably disable CSM, as once you have the NVMe driver then CSM shouldn't be needed.

[Vlada011]

And what ASUS suggest for people who use only one Windows 10 UEFI.
To Enable or Disable CSM. Anyway settings are set to UEFI First...
I don't want mess with Secure Boot only about CSM.
30-35 rear 38 seconds are not bad boot time for SATA III SSD and motherboard with so many functions.

[Chino]

If I recall correctly, you must disable CSM before installing Windows 10. If you installed Windows 10 with it on, then it won't let you disable it.

[emsir]

Chino wrote:
If I recall correctly, you must disable CSM before installing Windows 10. If you installed Windows 10 with it on, then it won't let you disable it.

Not true. You can disable CSM anytime you like, and enable it too.