Power down
Power down, shut off, switch off, or turn off are all terms describing 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's important to power down your computer by saving any unsaved documents, closing all running programs, and choosing the "Shut down" option in your operating system.
Pictured is a power button on the front of a computer. The universal power button symbol is a vertical line going through the circle, as shown in this picture. The power button turns your computer on, off, or cuts 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, 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: 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, there usually is a message stating not to turn off the computer while installing updates. If you do turn off the computer or the computer loses power, 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 (basic input/output system) or firmware update, the computer or hardware may stop working and may require a hardware replacement.