To shut down or power off a computer is to remove power from a computer's main components in a controlled way. After a computer is shut down, main components such as CPUs, RAM modules and hard disk drives are powered down, although some internal components, such as an internal clock, may retain power.
In Microsoft Windows, a PC or server is shut down by selecting the Shutdown item from the Start menu on the desktop. Options include shutting down the system and powering off, automatically restarting the system after shutting down, or putting the system into stand-by mode. There is also a
shutdown command that can be executed within a command shell window. shutdown.exe is the command-line shutdown application that can shut down the user's computer or another computer on the user's network.
Just like other operating systems, Windows has the option to prohibit selected users from shutting down a computer. On a home PC, every user may have the shutdown option, but in computers on large networks (such as Active Directory), an administrator can revoke the access rights of selected users to shut down a Windows computer. Nowadays there are many software utilities which can automate the task of shutting down a Windows computer, enabling automatic computer control. The Windows Shutdown website lists various software utilities to automate the task of shutting down.
In Windows, a program can shut down the system by calling the ExitWindowsEx or NtShutdownSystem function.
Mac OS X
In Mac OS X the computer can be shut down by choosing "Shut Down…" from the Apple Menu or by pressing the power key to bring up the power management dialog box and selecting button "Shut down". An administrator may also use the Unix
shutdown command as well. It can also be shut down by pressing [Alt]+[Command]+[Eject optical disc on optical drive] but this will not prompt the user anything at all.
Unix and Linux
One commonly issued form of this command is
shutdown -h now, which will shut down a system immediately. Another one is
shutdown -r now to reboot. Another form allows the user to specify an exact time or a delay before shutdown:
shutdown -h 20:00 will turn the computer off at 8:00 PM, and
shutdown -r -t 60 will automatically reboot the machine within 60 seconds (one minute) of issuing the command.
- Spolsky, Joel (21 November 2006). "Choices = Headaches". Joel on Software. Retrieved 25 August 2010.
- shutdown.cc – an article about various ways of automated and manual shutting down of Microsoft Windows