Microsoft reminded customers on Monday that users of the free preview version of Windows 7 need to pay for a system update, otherwise the operating system will begin to automatically shut down PCs in one month.

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

Microsoft had warned that Windows 7 RC would expire June 1, 2010. However, prior to that date, users will receive warnings to update. As of 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.

Microsoft Software