A hard reboot is restarting a computer without the usual shut-down procedure. It occurs when switching the computer off and on again, or, on some systems, by pressing Control-Alt-Delete or a special reset button. It may be caused by power failure, done by accident, or used because nothing else works.
A hard reboot is a full restore of a handheld computer (or PDA) to its factory settings. It entails deleting all information stored in the handheld. This is essentially the same as reformatting a hard drive. A hard reboot may become necessary from time to time on a PDA which has too many unreliable programs on it, thus restoring integrity to the system. It should be used with caution, as it destroys all data stored in the unit.