If you want to know how long your Windows XP Professional system has been running since the last reboot, you can run the command line version of System Information. Unlike its GUI counterpart, the command line version offers System Up Time information.
In a command prompt window, type Systeminfo. Near the top of the report that displays on the screen, you'll find an item titled System Up Time that tells you in days, hours, minutes, and seconds how long the system has been running since the last reboot.
If you'd rather not visually sort through the report to track down the System Up Time, you can pipe the Systeminfo report through the DOS-based Find command to get this information. Open a command prompt window, and type the following command:
Systeminfo | Find "System Up Time:"
Note: The command line version of System Information is only available in Windows XP Professional.