Remember that you can only use the Upgrade versions of Windows Vista and Windows 7 if you already have a qualifying version of Windows installed on the computer to upgrade it. Those versions of Windows won’t install on a blank hard drive or SSD; the Upgrade version has to be able to detect a version of Windows that qualifies to be upgraded to Windows 8.1. Therefore, you should always have a restorable system image or full backup that can be put back on a hard drive or SSD that was formatted due to a system failure or that can be restored to a new drive.
Windows 8.1 and 8.1 pro and 8.1 OEM only come in full versions, which means that they can be used to upgrade Windows 7 or perform a clean installation. If you’re running Windows Vista or Windows XP, you can’t perform an in-place upgrade, you have to perform a clean installation from Windows 8.1/Pro on a DVD that you create from the downloaded ISO file bought online from the Microsoft Store. The Windows 8.1 Pro Pack upgrades Windows 8.1 to the Pro version.
