As of 2015, a user can install Windows without the activation key but has a period of 30 days to activate it. If Windows is not activated during the 30-day period, the program stops working until the user activates it.
Activating Windows on a computer helps to verify that it is genuine and has not been installed on more than the maximum number of computers that Microsoft allows. The activation key usually comes with a new computer or with the Windows package. Those who buy Windows online can find the activation key in the confirmation email. A user can activate Windows via a direct connection, a modem or Microsoft's automated telephone system.