It is the OS that wouldn't die. It sounds like a horror movie, and for Microsoft, it probably seems like one. Microsoft announced on Monday that the "Windows XP Downgrade rights," which allows a purchaser of Windows 7 to choose to downgrade their OS to Windows XP, without paying for two copies of Windows, would continue until 2020.

In the past, Microsoft has terminated such a program a few months after the "next, next" version of Windows was introduced (in this case, 7, which was released in Oct. 2009). The problem is that 74 percent of businesses have not transitioned off of Windows XP, and many businesses want to standardize on a single operating system to simplify IT support.

The new policy, Microsoft announced in a blog post, will allow customers to downgrade to either Windows XP or Vista throughout the life cycle of Windows 7. Windows 7 Professional won't retire until 2020, which means XP will have a life that spans nearly 20 years (it was introduced in 2001).

Downgrade rights are available only for OEM copies of Windows 7 (those that are pre-installed by manufacturers or system builders). Also, despite this extension, while currently some vendors have been pre-installing the downgrade copy of Windows, that factory-install feature will expire on Oct. 22, 2010. That means that Windows users who want to downgrade a Windows 7 system to XP will be forced to do it themselves beginning on Oct. 23 of this year.

At the same time, OEMs must stop installing Windows XP Home on netbooks as of Oct. 22, 2010; finally, those netbook vendors may sell PCs with Vista pre-installed only through Oct. 22, 2011.