To shut down or power off a computer is to remove power

Switch

In electronics, a switch is an electrical component that can break an electrical circuit, interrupting the current or diverting it from one conductor to another....

 from a computer's main components in a controlled way. After a computer is shut down, main components such as CPU

Central processing unit

The central processing unit is the portion of a computer system that carries out the instructions of a computer program, to perform the basic arithmetical, logical, and input/output operations of the system. The CPU plays a role somewhat analogous to the brain in the computer. The term has been in...

s, RAM

Random-access memory

Random access memory is a form of computer data storage. Today, it takes the form of integrated circuits that allow stored data to be accessed in any order with a worst case performance of constant time. Strictly speaking, modern types of DRAM are therefore not random access, as data is read in...

 modules and hard disk drives are powered down, although some internal components, such as an internal clock, may retain power.

Windows

In Microsoft Windows

Microsoft Windows

Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...

, a PC or server is shut down by selecting the Shutdown item from the Start menu

Start menu

The Start Menu and Start Button are user interface elements used in the later versions of the Microsoft Windows operating systems and in some X window managers...

 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 network computers, 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.

Mac OS X

In Mac OS X

Mac OS X

Mac OS X is a series of Unix-based operating systems and graphical user interfaces developed, marketed, and sold by Apple Inc. Since 2002, has been included with all new Macintosh computer systems...

 the computer can be shut down by choosing "Shut Down…" from the Apple Menu

Apple menu

The Apple menu has been a feature in Apple's Mac OS since its inception. It is the first item on the left hand side of the menu bar. The Apple menu's role has changed throughout the release history of Mac OS, but the menu has always featured a version of the Apple logo.-System 6 and earlier:In...

 or by pressing the power key to bring up the power management dialog box. An administrator may also use the Unix shutdown command

Command (computing)

In computing, a command is a directive to a computer program acting as an interpreter of some kind, in order to perform a specific task. Most commonly a command is a directive to some kind of command line interface, such as a shell....

 as well.

Unix and Linux

In Unix

Unix

Unix is a multitasking, multi-user computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs, including Ken Thompson, Dennis Ritchie, Brian Kernighan, Douglas McIlroy, and Joe Ossanna...

 and Linux

Linux

Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...

, the shutdown command can be used to turn off or reboot

Booting

In computing, booting is a process that begins when a user turns on a computer system and prepares the computer to perform its normal operations. On modern computers, this typically involves loading and starting an operating system. The boot sequence is the initial set of operations that the...

 a computer. Only the superuser

Superuser

On many computer operating systems, the superuser is a special user account used for system administration. Depending on the operating system, the actual name of this account might be: root, administrator or supervisor....

can shut the system down.

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.

External links

• shutdown.cc – an article about various ways of automated and manual shutting down of Microsoft Windows