Uptime is the length of time that your operating system has been up and running. In other words, how long has it been since the last reboot? If you rarely reboot your computer, you may be interested in finding out how long Windows XP has been running. You can accomplish from the command prompt by using the systeminfo command as described below.
From the Start menu, click Run. Type “cmd” and click OK. From the Command Prompt window, type systeminfo | find “Up Time” and press Enter. The results will tell you how long Windows XP has been up and running. As with many other commands, it is case sensitive so it must be typed in exactly as it appears above or an error message will be returned instead.