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bcdboot C:\Windows /s X: /f ALL MBR vs GPT Legacy BIOS vs UEFI Bios RRS feed

  • Question

  • I have some questions about usage of  the BCDBOOT command with the switches: bcdboot C:\Windows /l en-us

    /s X: /f ALL 

    where X: is the system partition volume letter or drive letter(assume it's S:)

    Here's what Microsoft's own documentation says:

    " If you specify the /f option, you must also specify the /s option to identify the volume letter of the system partition."

    Where, the system volume in a UEFI Bios is a fat32 Partition known as the EFI ESP , where ESP stands for EFI System Partition...

    Is this correct? yes or no?

    let me qualify it more from Microsoft Documentation:

    /f <firmware type>

    Optional. Specifies the firmware type. Valid values include UEFI, BIOS, and ALL.

    On BIOS/MBR-based systems, the default value is BIOS. This option creates the \Boot directory on the system partition and copies all required boot-environment files to this directory.

    On UEFI/GPT-based systems, the default value is UEFI. This option creates the \Efi\Microsoft\Boot directory and copies all required boot-environment files to this directory.

    When you specify the ALL value, BCDBoot creates both the \Boot and the \Efi\Microsoft\Boot directories, and copies all required boot-environment files for BIOS and UEFI to these directories.

    So based on this additional documentation:

    QUESTIONS

    If I use diskpart to create this system partition I can create it as either a MBR disk or a GPT disk, based on the BIOS TYPE.

    I know it has to be formatted as FAT32? Correct? For both MBR and UEFI disk partition types. Correct?

    I can always convert gpt to mbr or mbr to gpt within diskpart. Yes?

    If I were to use /f UEFI, the disk would have to be created as a GPT disk? Correct?

    IF I had an older BIOS, and use /f BIOS,  I would create the disk as  a MBR disk. Correct?

    IF I had an UEFI BIOS that has CSM support ENABLED, Compatibility Support Module (CSM), which disk partition type should I use? 

    I have read that you cannot set a GPT disk ACTIVE?  Is that TRUE?

    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. OR take a UEFI disk and have it boot in a BIOS system. Is this TRUE? 

    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.

    Because the BIOS is EMULATED by CSM in a UEFI 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.

    Comments? 

    More questions.

    Questions

    It's my understanding that BCDBoot ONLY copies the contents of BOTH  \Boot and/or \EFI\Microsoft\Boot to the system partition if /f All is selected.

    IF BIOS is selected is ONLY the \Boot contents copied ? 

    IF UEFI is selected is ONLY the \EFI\Microsoft\Boot contents copied ?

    When using /f ALL should the system partition be created as MBR or GPT, depending on the BIOS type i.e.

    BIOS versus UEFI BIOS(with CSM Enabled) vs UEFI BIOS(with CSM Disabled) ?

    In addition to doing the BCDBoot Command, should I also do the following command?

     bootsect /nt60 S: To write the boot sector to the System Partition? To make it bootable?

    Do I also set it as the ACTIVE Partition whether or not it's MBR or GPT?

    what's the difference between using the  bootsect /nt60 S: command vesus using:

    bootsec /fixmbr

    bootsec /fixboot

    Do I also need to :

    bootrec /rebuildbcd ?

    I know that I am asking a lot here. So anybody who knows the answers to ALL or most of these questions will be greatly appreciated. TIA

    Wednesday, May 29, 2019 4:03 AM

Answers

  • Hi,
    How things are going there on this issue?
    Please let me know if you would like further assistance.

    Best regards,

    Hurry


    Please remember to mark the reply as an answer if they help.
    If you have feedback for TechNet Subscriber Support, contact tnmff@microsoft.com


    • Marked as answer by rocketjetz Friday, June 7, 2019 11:19 PM
    Saturday, June 1, 2019 12:02 PM

All replies

  • Hi,

    Thank you for posting in Microsoft TechNet Forum.

    On GPT drives, this is known as the EFI System Partition, or the ESP. This partition is usually stored on the primary hard drive. The device boots to this partition. The minimum size of this partition is 100 MB, and must be formatted using the FAT32 file format.

    Yes. You can convert GPT to MBR or MBR to GPT within diskpart

    If you were to use /f UEFI, the disk would have to be created as a GPT disk.

    You would need to create the disk as  a MBR disk if using /f BIOS. IF you had an UEFI BIOS that has CSM support ENABLED, Compatibility Support Module (CSM), you should use GPT disk partition type. 

    If users are running an MBR disk, only the primary partitions on it can be set active. But if the disk is GPT, there's no such limit.

    Yes. 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.

    You can refer to the article: How to Set Active/Inactive | MiniTool Partition Wizard Tutorial

    /nt60 – use nt60 to repair the boot sector for Windows Vista, 7, 8, or 10. The full command would be: bootsect /nt60 S:, where S: is the drive’s letter. Maybe the difference is that locate drive letter.

    Meanwhile, please refer to the following link which may help:

    https://fossbytes.com/uefi-bios-gpt-mbr-whats-difference/

    Note: This is a third-party link and we do not have any guarantees on this website. This is just for your convenience. And Microsoft does not make any guarantees about the content.

    Hope the above information will help you.

    Best regards,

    Hurry


    Please remember to mark the reply as an answer if they help.
    If you have feedback for TechNet Subscriber Support, contact tnmff@microsoft.com


    Thursday, May 30, 2019 8:39 AM
  • If your CSM is set to boot the HDD via UEFI or CSM is disabled, you create GPT disk and use bcdboot w:\windows /s s: /f all or bcdboot w:\windows /s s: /f uefi

    If your CSM is set to boot the HDD via Legacy, or using a BIOS system, you create MBR disk and use bcdboot w:\windows.

    Thursday, May 30, 2019 4:26 PM
  • Hi,
    How things are going there on this issue?
    Please let me know if you would like further assistance.

    Best regards,

    Hurry


    Please remember to mark the reply as an answer if they help.
    If you have feedback for TechNet Subscriber Support, contact tnmff@microsoft.com


    • Marked as answer by rocketjetz Friday, June 7, 2019 11:19 PM
    Saturday, June 1, 2019 12:02 PM
  • Hi,

    Is there anything else I can do to help you on this issue?

    Please feel free to contact me if you have any questions.

    Best regards,

    Hurry


    Please remember to mark the reply as an answer if they help.
    If you have feedback for TechNet Subscriber Support, contact tnmff@microsoft.com

    Monday, June 3, 2019 9:29 AM