/allowFullOS– by default, the MBR2GPT can be used only in Windows PE.You can specify multiple mappings at once The number of the MBR partition is specified in decimal notation, and GPT GUID contains delimiters. /map:- allows you to specify additional partition table mappings between MBR and GPT.

The log files are diagerr.xml, diagwrn.xml, setuperr.log and setupact.log If the path is not set, the %windir% folder is used. /logs:- specifies the path to the directory where MBR2GPT should write log files.If the number is not set, the system disk will be converted (like Diskpart command: select disk system) /disk:- specifies the number of the disk to be converted into GPT./convert– starts converting the disk if the validation has been successful./validate– the disk is only validated if the partition table can be converted (including the check of free space to store the primary and the secondary GPT table: 16 KB + 2 sectors in the beginning of the disk and 16 KB + 1 sector in the end).The BCD bootloader configuration is updated.GPT metadata and partition table are applied to the disk (the MBR partition table is converted to GPT without losing data on existing partitions).

UEFI boot files are copied to the EFI partition.If there is no EFI (ESP) system partition, it is created using free space from one of the partitions (if there is not enough free space, an error message will appear “ cannot find room for the EFI system partition”).The logic of Mbr2gpt when converting an MBR disk to a GPT is as follows: The BCD configuration must have a boot record pointing to a Windows partition.The MBR table should contain no more than 3 partitions, one of which is active (additional and logical partitions should be missing).There is free space on the disk for placing the primary and secondary GPT tables at the beginning and end of the disk.The MBR2GPT documentation says, that the following conditions must be met to convert a disk partition table to GPT:

But to convert a system disk, you had to completely clean up the disk, create GPT partition table and new partitions on it, and then perform a clean install of Windows 10. Earlier, a third-party tool gptgen, could be used to convert a non-system disk from MBR to GPT without losing existing partitions.

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