After updated to Windows 10 on your computer, there is a folder named Windows.old to store your old Windows environment like Windows 7 or Windows 8 and 8.1. This folder is used to roll back to previous Windows version when you click Get Started under Recovery. By default, Windows.old will be deleted after 1 month after upgrade successfully. Except the default setting, we can manually delete Windows.old by checking Previous Windows installation(s) at Disk clean-up as administrator right to delete Windows.old.
After deleting Previous Windows installation(s), you cannot roll back to previous Windows version. Make sure your Windows 10 environment is stable before deleting Windows.old.
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