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  1. #1
    ROG Member Array otec PC Specs
    otec PC Specs
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    What is CSM and do I need it enabled?

    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!

  2. #2
    ROG Guru: Grand Master Array
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    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]

  3. #3
    ROG Member Array otec PC Specs
    otec PC Specs
    MotherboardAsus Z170 Deluxe
    ProcessorIntel i6700K
    Memory (part number)Team Group Xtreem 2x8GB 3733Mhz
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    Sound CardSOUND BLASTER ZXR
    MonitorDell 5K
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    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?

  4. #4

  5. #5
    ROG Guru: Brown Belt Array Vlada011 PC Specs
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    MotherboardRampage V E10 (BIOS 1903)
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    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.


  6. #6
    ROG Guru: Grand Master Array
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    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.

  7. #7
    ROG Guru: White Belt Array aceisme PC Specs
    aceisme PC Specs
    MotherboardASUS Maximus VIII Hero
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    A UEFI system can boot only from a GPT disk, not MBR. A BIOS system can boot only from an MBR disk and not GPT, which is why you can't take an OS disk from a BIOS system and put it in a UEFI system and expect the system to boot.
    Most UEFI motherboards come with a Compatibility Support Module (CSM), which is enabled by default. It makes the motherboard actually look like a BIOS system, allowing it to boot from NTFS and MBR disk, but you lose the UEFI features and are essentially just using BIOS. If you want to run your system as UEFI, you need to disable the CSM via the motherboard's interface before you install Windows.
    Your UEFI system can boot only from a device that has an EFI boot loader, so after the CSM has been disabled, the only boot devices that are listed will be UEFI aware.
    After Windows is installed, msinfo32 (System Information) will show the BIOS mode as UEFI, not legacy.

  8. #8
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    Quote Originally Posted by aceisme View Post
    A UEFI system can boot only from a GPT disk, not MBR. A BIOS system can boot only from an MBR disk and not GPT, which is why you can't take an OS disk from a BIOS system and put it in a UEFI system and expect the system to boot.
    Most UEFI motherboards come with a Compatibility Support Module (CSM), which is enabled by default. It makes the motherboard actually look like a BIOS system, allowing it to boot from NTFS and MBR disk, but you lose the UEFI features and are essentially just using BIOS. If you want to run your system as UEFI, you need to disable the CSM via the motherboard's interface before you install Windows.
    Your UEFI system can boot only from a device that has an EFI boot loader, so after the CSM has been disabled, the only boot devices that are listed will be UEFI aware.
    After Windows is installed, msinfo32 (System Information) will show the BIOS mode as UEFI, not legacy.
    That being said if I were installing Windows 10 on a 970Evo 500GB NVMe M.2 in a ROG Maximus X Formula, would I need to change CSM to disabled and then under secure boot chnage the OS type to "other type" and clear secure boot keys?

  9. #9
    Banned Array JustinThyme PC Specs
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    I cant speak directly from your board but on a similar buid 7700K and M9F I had to leave the CSM enabled to get it to boot from the USB. Dont remember having issues later setting to disabled. When windows wont boot on any issue like this whats worked for me is to go back a step, let windows boot, reboot to safe mode, then turn CSM off and save and exit. Then it willl boot in safe mode. restart...done

  10. #10
    ROG Guru: Gold Belt Array Menthol PC Specs
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    I can verify changing CSM to disable after Win 10 installation

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