Asus TUF Z270 MARK 2 Bios Manual page 60

CSM (Compatibility Support Module)
support the various VGA, bootable devices and add-on devices for a better compatibility.
Launch CSM
[Auto]
[Enabled]
[Disabled]
The following items appear only when you set the Launch CSM to [Enabled].
Secure Boot
OS Type
[Windows UEFI Mode]
The Microsoft secure boot only supports Windows UEFI mode.
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The system will automatically detect the states of bootable devices
and the add-on devices for CSM support.
For a better compatibility, enable the CSM to fully support the non-
UEFI driver add-on devices or the Windows UEFI mode.
Disable the CSM to fully support the Windows secure update and
secure boot.
Boot Devices Control
This item allows you to select the type of devices that you want to boot.
Boot from Network Devices
This item allows you to select the type of network devices that you want to
launch.
Boot from Storage Devices
This item allows you to select the type of storage devices that you want to
launch.
Boot from PCI-E/PCI Expansion Devices
This item allows you to select the type of PCI-E/PCI expansion devices that
you want to launch.
[UEFI only]
This item allows you to execute the Microsoft secure
boot check. Only select this option when booting on
Windows UEFI mode or other Microsoft secure boot
compliant OS.
Windows non-UEFI mode and Microsoft secure boot
non-compliant OS.
ASUS TUF Z270 MARK 2 BIOS Manual