Microsoft allows the user to run a copy of Windows XP for 30 days before requiring the user to enter an official activation key. After the 30-day trial period expires, Microsoft prevents Windows XP from running until the user provides an official activation key.
If a computer shipped from the factory with Windows XP installed, the activation key is usually found on a sticker located somewhere on the computer. For machines that had Windows XP installed later, the activation key is found inside the software's packaging. Microsoft allows activation of Windows XP copies using the Internet, a dial-up modem or via a telephone hotline.