On *nix system the command uptime is quite well known, but on windows there is no such command, at least not out of the box.

There are a couple of ways to work around this shotcomming:

1. you can execute systeminfo on cmd.exe and search for System Up Time
2. you can execute net statistics server and look for the time, since when the local server has been running
3. you can install uptime.exe from Microsoft