1. A reboot is the process of restarting a working computer using hardware (e.g. a power button) instead of software. Rebooting is sometimes necessary after installing a software program, installing operating system updates, to recover from an error, or to re-initialize drivers or hardware devices.
A hard reboot vs, or soft reboot
A reboot may be a cold reboot or hard reboot, which means the power was physically shut off and then turned back on. It can also be a warm reboot or soft reboot, which means the system restarted without loss of power.
Note: Users should only perform a hard reboot if the computer is completely frozen, as it may damage hardware components.
How to do a hard reboot
To perform a hard reboot or cold reboot, press and hold down the power button on the computer. After 5-10 seconds, the computer should turn off. Once the computer is off, wait a few seconds and then turn the computer back on.
What key combination allows me to restart
For PCs you can press Ctrl + Alt + Del (known as three finger salute) to reboot the computer or start the process of rebooting or restarting the computer.
Reboot vs. Restart
The term restart refers to an operating system closing all programs before a soft reboot. The image shows the "Turn off computer" prompt in Windows XP, with the previously mentioned Restart option.
2. Linux users see the reboot command for further information.