Disabling CSM (Legacy) support in UEFI

Discussion in 'Windows 10' started by x86, Mar 17, 2018.

  1. x86

    x86 MDL Addicted

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  2. Tito

    Tito Super Mod / Adviser
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    Nov 30, 2009
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    @x86

    Any task which isn't optimised for pure UEFI environment, such as working with some addon cards with legacy option roms.
     
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  3. x86

    x86 MDL Addicted

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    Thank you Tito. But I can still disable CSM, install W10 - and if I ever need to re-enable it - it should be OK, right?
    In such case, would it cause any issue to the OS if I was to re-enable Legacy support at a later stage?
     
  4. TigTex

    TigTex MDL Member

    Oct 5, 2009
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    You can't boot any MS-DOS tool without CSM support enabled. For example, hdat2 to check and repair bad hard disks.
    Always keep CSM support disabled unless your hardware/software doesn't work without it. You can switch between CSM on and off if your windows is installed in UEFI / GPT mode. BIOS / MBR will fail to boot with CSM disabled
     
  5. x86

    x86 MDL Addicted

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    Clear. I ll fresh install Win10 x64 in pure UEFI and then - if needed - I ll turn CSM on (if such demand arises). Haven't had to boot any DOS-based tool for a looong time. It was only needed recently, when I used the Secure Erase Samsung utility.

    I created this post, because I thought enabling CSM would (somehow) alter the behaviour of the installed OS, by adding unnecessary burden (to a UEFI compliant OS - such is Win10...). My assumption was wrong.
     
  6. Tito

    Tito Super Mod / Adviser
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    As you've speculated already, no - there shouldn't be any issue.
     
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  7. LatinMcG

    LatinMcG Bios Borker

    Feb 27, 2011
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    no need to wipe fresh.. convert to GPT and that should do it.
     
  8. x86

    x86 MDL Addicted

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    Sorry - I was refering on a new build. There's currently no OS on it, so fresh install is only option.
     
  9. GodHand

    GodHand MDL Senior Member

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    There's no need for CSM unless you require legacy compatibility.
     
  10. d5aqoëp

    d5aqoëp MDL Member

    Jan 19, 2017
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    If you are installing Windows 10 on Z87 and newer chipsets, disabling CSM is the best way forward to have a true UEFI booting system which not only boots faster but is slightly more secure.

    Things needed for True UEFI boot:
    1. Disable CSM in BIOS. (Some motherboards like MSI don't have a straightforward way to disable CSM but there you need to disable Windows 7 boot mode and use Windows 8/10 WHQL mode)
    2. Make bootable Windows 10 USB with Rufus and select GPT partition scheme for UEFI
    3. Format your hard drive and convert it to GPT style

    How to format your hard drive?
    Click repair at the beginning of Windows 10 setup and start command prompt.
    Code:
    diskpart
    list disk
    select disk x (whichever disk you want to use for installing windows)
    clean
    convert gpt
    Proceed to install Windows

    I am on this mode for 3 years and I absolutely don't see a reason to enable CSM ever again unless I am installing Windows 7 for teh lulz.
     
  11. Enthousiast

    Enthousiast MDL Tester

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    I don't get why people always feel the need to use all kinds of hoops to get a system installed.

    When you boot up from a FAT32 formatted USB containing the extracted ISO and you're running with pure UEFi settings. you just have to delete all existing partitions on the system drive and repartition, it will repartition with the UEFI partition table.
    You only need to keep all other hdd's disconnected for being able to do this, on laptops there is most likely just one drive so that shouldn't be a problem.
     
  12. Tiger-1

    Tiger-1 MDL Guru

    Oct 18, 2014
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    hmm here I always make install in UEFI mode with my SSD and several hdd"s and never had issues
     
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  13. Enthousiast

    Enthousiast MDL Tester

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    If you don't switch partitioning tables, there will be no problem ;)
     
  14. GodHand

    GodHand MDL Senior Member

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    Yeah and it will size the partitions using parameters which are not even optimal per Microsoft's partition layout guidelines. Just spend the additional 2 minutes to create a script or set up a device so the disk layout is optimal, for crying out loud.

    For systems that I physically install an OS on, or when I do not want to fiddle with an unattend.xml or cannot access my network for some reason, I usually just toss a DiskPart script into the USB and run it at the setup screen, where it quickly formats any drives to the specifications within.

    Code:
    select disk 0
    clean
    convert gpt
    create partition efi size=100
    format quick fs=fat32 label="System"
    create partition msr size=128
    create partition primary
    shrink minimum=500
    format quick fs=ntfs label="WinOS"
    assign letter="C"
    create partition primary
    format quick fs=ntfs label="WinRE"
    set id="de94bba4-06d1-4d40-a16a-bfd50179d6ac"
    gpt attributes=0x8000000000000001
    list volume
    exit
    
    Here's a very basic one with proper partition sizes and assigns the Recovery (WinRE) partition as the last partition on the drive. The "shrink minimum=500" can be adjusted depending on the size of your recovery image, as some use custom recovery images as opposed to Windows' default one. Or that line can be appended so it creates a new partition for the recovery drive in whatever location one needs. Just make sure the "select disk 0" is changed to the disk you are installing Windows on. "WinOS" and "WinRE" can also be changed to whatever partition names desired. Save the file as "CreatePartitions.txt" and place it at the root of your USB drive.

    To run it, you just Shift+F10 at the setup screen to bring up DOS-prompt, navigate to the root of the USB drive and type "diskpart /s CreatePartitions.txt" and it will quickly create all the partitions assigned. If it says it cannot assign drive letter 'C' because it's not available, just continue to install Windows and it will automatically set the Windows drive as 'C' after installation completes.
     
  15. Enthousiast

    Enthousiast MDL Tester

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    Oh there is "social interaction extraordinaire." with more useless info.
     
  16. macnavarra

    macnavarra MDL Member

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    #17 macnavarra, Mar 22, 2018
    Last edited: Mar 23, 2018
    Personaly i never tryed to install windows 10 in UEFI boot with a HardDrive larger then 2TB.
    But i guess the windows 10 setup should Partition it in GPT.