In computing, a reboot refers to restarting a device. A reboot can be a soft reboot or a hard reboot.

Soft Reboot

A soft reboot (also known as a warm reboot, in contrast to a cold reboot) is restarting a computer under software control, without removing power or (directly) triggering a reset line. It usually, though not always, refers to an orderly shut-down, rather than a "reboot".

The Control-Alt-Delete key combination on the original IBM PC was designed to allow a soft reboot for a quicker and more convenient (and, some argue, less stressful on system components) restart than powering the computer completely down then back up.

Hard Reboot

A hard reboot, or "cold reboot" is when power to a computer is cycled or a special reset signal to the processor is triggered. This restarts the computer without first performing the usual shut-down procedure. With many operating systems, especially those with disc caches, after a hard reboot the system may well be in an "unclean" state, and require that checks and repairs to on-disc filesystem structures be performed before normal operation can begin.

Hard reboots may be caused by power failure, be done by accident, or be done deliberately as a last resort because nothing else to retrieve the system from a "hung" state works.

This article is adapted from: wikiPedia.com.