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 then 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.
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