Hello,
Diskpart general information can be found here: https://learn.microsoft.com/en-us/windows-server/administration/windows-commands/diskpart
All all, for Windows installations, is usually more confortable to manage the partitions from the Custom installation process when proceeded with the Windows installation. This will allow to delete not desired partitions (Reserved, System, etc) and Windows to create the right additional partitions for the system.
To delete the current partition:
At a command prompt, type diskpart
At the DISKPART prompt, type select disk 0 (Selects the disk.)
At the DISKPART prompt, type list partition
At the DISKPART prompt, type select partition <Number of the desired partition>
At the DISKPART prompt, type delete partition
At the DISKPART prompt, type exit
To partition again the space, you will need:
At a command prompt, type: diskpart
At the DISKPART prompt, type list disk (Note the drive number you wish to manipulate.)
At the DISKPART prompt, type: select disk 0 (This selects disk to edit; make sure to type in the disk number from step two.)
At the DISKPART prompt, type create partition primary size=100000 (The size parameter refers to the size in megabytes. In this case, 100000 equals 100 GB. Change the word primary to extended to create an extended partition. If you do not set a size, then all available space on the disk will be used for the partition.)
At the DISKPART prompt, type assign letter=D (Choose an unused drive letter.)
At the DISKPART prompt, type exit
From the command prompt, use the format command, or the Disk Management utility in Windows or any disk format tool to format the drive.
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