Last year's free preview of Windows 7 will start nagging users to pay for the operating system in two weeks, and begin automatically shutting down PCs in one month, Microsoft reminded customers today.

Microsoft unveiled the schedule for Windows 7 Release Candidate's retirement in May 2009, when it issued the early look to the public.

At the time, it said Windows 7 RC would expire June 1, 2010. Before that date, however, users are to receive warnings of the impending end. Starting on Feb. 15, Windows 7 RC will display notices every few hours that the machine will periodically shut down beginning on March 1.

As of March 1, PCs running Windows 7 RC will automatically shut down every two hours. Those shutdowns will come without warning.

"To avoid any data loss, I suggest making plans to move to a released version of Windows 7 before the automatic shutdowns start [on March 1]," said Microsoft spokesman Brandon LeBlanc in an entry on the Windows 7 blog today. "During these shutdowns, your work will not be saved."

From March 1 to June 1, the automatic shutdowns will continue. On June 1, Windows 7 RC is tagged as "not genuine" -- Microsoft's term for counterfeit -- and boots to a solid black screen that shows a Windows Activation screen.

To make matters tougher for users still running the free version, Microsoft does not allow in-place upgrades from the RC to a paid copy. Instead, users must back up their data, do a clean install -- Microsoft calls it a "custom install" -- that erases the contents of the hard drive before it installs the operating system, then restore the backed-up data and reinstall all applications.

Microsoft has previously confirmed that customers can use the less-expensive upgrade editions of Windows 7 to migrate from the RC to a paying copy. Windows 7 Home Premium Upgrade , for example, lists for US$110.99 on Amazon.com, a $69 savings over the $179.99 for Windows 7 Home Premium.