How to know the running time of windows

Hi friends, Most of us are interested to know that for how much time his window is working. That means, it will tell you the time between your current system time and the time when you started your PC after shut down. In case of hibernate, when you hibernate the system, time stops running and starts again at resumption of window. Although, this trick is old but is less observed by anyone and is very useful. Its not useful in the sense that you will need it