Just a day before Microsoft drops support for Windows XP Service Pack 2 (SP2) , the company announced on Monday that people running some versions of Windows 7 can "downgrade" to the aged operating system for up to 10 years.
The move is highly unusual. In the past, Microsoft has terminated downgrade rights -- which let customers replace a newer version of Windows with an older edition without paying for two copies -- within months of introducing a new OS.
While few consumers may want to downgrade from Windows 7 to XP -- unlike when many mutinied against Vista three years ago -- businesses often want to standardize on a single operating system to simplify machine management.
Monday's announcement was the second Windows XP downgrade rights extension. Microsoft originally limited Windows 7-to-Windows XP downgrades to six months after Windows 7's release, but backtracked in June 2009 after an analyst with Gartner Research called the plan a "real mess."
Instead, Microsoft later said it would allow downgrades to Windows XP until 18 months after the October 2009 debut of Windows 7 , or until it released Windows 7 SP1.
In either scenario, XP downgrade rights would have expired sometime in 2011, perhaps as early as April.
On Monday, Microsoft again changed its mind. Users running Windows 7 Professional or Ultimate will now be able to downgrade to Windows XP Professional throughout the entire lifecycle of Windows 7.
"Our business customers have told us that the removing end-user downgrade rights to Windows XP Professional could be confusing," said Microsoft spokesman Brandon LeBlanc, in an entry on the a company blog .
Windows 7 Professional won't be fully retired until January 2020; the Ultimate edition will be put out to pasture five years earlier, in January 2015.
Although Microsoft said it made the change to simplify the work in tracking licensing rights for PCs, the continued popularity of Windows XP may have had something to do with it. At the Worldwide Partner Conference (WPC), which opened Monday in Washington D.C., a company executive acknowledged that 74% of business computers still run XP.
The downgrade rights are available only from OEM copies of Windows 7, those that are pre-installed by computer makers.
"Going forward, businesses can continue to purchase new PCs and utilize end-user downgrade rights to Windows XP or Windows Vista until they are ready to use Windows 7," LeBlanc added in his blog post.
The change impacts only consumers and businesses that don't subscribe to Software Assurance (SA) -- Microsoft's annuity-like upgrade guarantee program -- or those who purchase Windows through volume-licensing plans. Those companies already had downgrade rights from any edition, including Windows 7, to any previous version going as far back as Windows 95.
Other deadlines that Microsoft had previously scheduled for Windows remain in place. Computer manufacturers must stop installing Windows XP Home on netbooks as of Oct. 22, 2010, and they may sell PCs with Vista pre-installed only through Oct. 22, 2011.
Computer makers are also slated to stop offering factory-installs of XP Professional downgrades on PCs with Windows 7 Professional licenses after Oct. 22, 2010. That means Windows users who want to downgrade a Windows 7 system to XP must do it themselves starting Oct. 23 of this year.
It's unlikely that many Microsoft customers, even the largest corporations, will downgrade to XP as long as Microsoft allows. That's because the nearly-nine-year-old operating system falls off the support list for good in April 2014.
On Tuesday, Microsoft will supply the last-ever updates for Windows XP Service Pack 2 (SP2), the 2004 upgrade that was superseded four years later by XP SP3.
However, some computer makers continue to sell new PCs with a factory-installed downgrade to Windows XP. Dell , for example, offers downgrades on some Latitude notebooks.
The practice was much more widespread when Microsoft marketed Windows Vista. Then, customers clamored for ways to return to XP after buying new PCs equipped with Vista, a rebellion that forced Microsoft to delay several times the end of XP availability to both large and smaller computer sellers.
Gregg Keizer covers Microsoft, security issues, Apple, Web browsers and general technology breaking news for Computerworld. Follow Gregg on Twitter at @gkeizer or subscribe to Gregg's RSS feed . His e-mail address is firstname.lastname@example.org .
Read more about windows in Computerworld's Windows Topic Center.