In 10 weeks, Microsoft Corp. will begin to retire Windows XP by shifting the seven-year-old OS into a more limited support plan.

Windows XP, Microsoft's most successful operating system ever, will leave what the company calls "mainstream support" on April 14, and enter "extended support." Typically, Microsoft keeps a product in the former for five years, then moves it into the latter for another five, for a total of 10 years. However, the long span between the releases of XP and its successor, Windows Vista, forced the company to push out the support deadline to 13 years altogether.

Also, two years ago Microsoft bumped support for Windows XP Home and XP Media Center to the 2009 and 2014 dates, matching the dates that had previously been set for Windows XP Professional, the designated business edition of the operating system.

By Microsoft policy, mainstream support delivers free fixes -- for security patches and other bug fixes -- to everyone. During extended support, all users receive all security updates, but non-security hot fixes are provided only to companies that have signed support contracts with Microsoft.

Microsoft has, in fact, issued a total of three service packs for the aged operating system, the most recent, Windows XP SP3 , in May 2008.