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Windows 10 was installed on Drive C. Drive E and F are almost full. I decided to downgrade to Windows 8, and made a bootable USB stick of the same. I'm a linux guy and my windows skills are rusty at best.

I booted using the Windows 8 stick and chose "Custom Install" and formatted my C drive. The installer then notified me that the drive isn't GPT and needs to be converted from MBR to GPT, which apparently requires a complete format. The "Regular" install option (which I glazed over) asks me to run the setup utility from the windows desktop(R.I.P).

Apart from copying my data over to another drive and installing Windows 8 after formatting the drive, the only other options are using Windows 10 recovery media or somehow mimicking the windows desktop to run the installer with the "Regular" option. Are either of these alternate cases viable? Can Windows 10 repair media "repair" my C drive? Can something start the "Regular" installer without repairing my C drive?

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After you have made a complete clone of your disk to preserve your data (Clonezilla works on FAT32, NTFS, and ext4 and is free), you MAY repeat MAY be able to convert your drive's partition table from MBR to GPT with gptgen, a la:

gptgen -c -w \\.\physicaldrive0
(if C: is Drive 0)

There are commercial products which claim to do it as well.

Alas, using Microsoft's old tool, diskpart, which is included with Windows, ever since Win2k, will probably trash your data. They have a new MBR2GPT tool available with Windows 10 since Build 1703 which will convert the partition table, but I don't know if that is available to you.

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  • Is there any way to convert the C partition into GPT and install windows 8 on it using linux? I've burnt CloneZilla to a thumb drive. – Mike Rosoft Jul 7 '18 at 12:45
  • Install Windows from Linux? No. Convert partition in Linux? Yes with gptgen as above. – K7AAY Jul 8 '18 at 18:06

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