For consumers, downgrade rights, which let customers replace a newer version of Windows with an older edition without paying for two copies, are available only in copies of Windows 8 Pro pre-installed on new PCs. On the other hand, corporations with enterprise licensing agreements, including the annuity-like Software Assurance, are always allowed to downgrade from any version of Windows to any previous edition.

Downgrade rights broke out of their enterprise niche to became a hot topic after Windows Vista's 2007 launch when many consumers on their PCs to run XP instead.

It was one of several signals that Vista was on shaky ground.

Compared to Vista, interest in Windows 7's downgrade rights has been minimal. Today, Windows 7 is the , with a share nearly two-and-a-half times that of Vista at its peak.

"For enterprises, downgrade rights are tremendously important [for Windows 8]," said Michael Silver, an analyst with Gartner. "Most of the traditional form factors -- desktops and notebooks -- will be downgraded. But if it gets so bad that consumers downgrade, that's a disaster for Microsoft. That means there's word in the public that [Windows 8] is just bad."