Windows uptime means the number of hours, days or weeks that the computer has been operating since the last reboot of the computer. This helps in finding out if your computer has been on for a while. To see the Windows uptime, follow these steps: Press the key combination Ctrl + Shift + Esc to launch Task Manager, go to the Performance tab, then click CPU, and you will see the uptime value there. You can also launch Command Prompt and run systeminfo | find "System Boot Time" to view the boot time of the system. Note that sometimes, due to Windows Fast Startup, the uptime does not reset correctly after a shutdown.