Read more at source:Microsoft will allow users of Windows 8 Pro to downgrade their new PCs to Windows 7 or even Vista, according to the operating system's licensing agreement.
Not surprisingly, users may not downgrade to the still-used-but-slated-for-retirement Windows XP.
Downgrade rights -- which let customers replace a newer version of Windows with an older edition without paying for two copies -- are available only in Windows 8 Pro. That fits with previous practice: Only Windows 7 Professional, for instance, was allocated downgrade rights.
Microsoft will allow downgrades from Windows 8 to Windows 7, Vista - Computerworld