Power down, shut off, switch off, or turn off are all terms used to describe the cessation of power to the computer. If the computer is powered off suddenly without properly initiating a shutdown from the operating system, data may be lost and important files may be corrupted. Therefore, it is important to always power down your computer by saving any unsaved documents, closing all running programs, and choosing the "Shut down" option in your operating system.
Pictured at right is a power button on the front of a computer. The universal power button symbol is a circle with a vertical line going through the circle as shown in this picture. This button can be used to turn your computer on, signal that you want to turn it off, or cut all power to the computer in response to an emergency or a serious error. Ideally, you should only use this button to turn on the computer; to turn it off, use your operating system software.
How to turn off a computer
With most computers, when you quickly press the power button once, the computer will power off automatically. If you need to turn off a computer because of a problem, you can press and hold the power button for a few seconds to turn it off.
To learn alternative ways to turn off (shut down) your machine, see our page on how to shut down a computer.
What happens if you turn off a computer when it says not to?
When a computer is performing important updates or other system changes, you'll see a message not to turn off the computer while installing updates. If you do turn off the computer, or the computer loses power, a number of different things can happen.
For example, while Microsoft Windows or another operating system is updating the computer, if you turn off the computer during the update, the files being updated may become corrupt. The corrupt files can cause the computer to have errors or not boot at all. If you turn off a computer during a BIOS or firmware update, the computer or hardware may stop working and may require a hardware replacement.