I bet you don’t know how to turn off your computer.

Lots of people ask me why their computer doesn’t turn off when they hit the power button on the front of the case after the system crashes or freezes. Hold the button down for 4-10 seconds. The computer will turn off even if it is otherwise completely unresponsive.

Let’s go through a little history to help you understand why that’s actually a feature.

Back in the old days, the power button on the case was directly wired to the computer’s power supply. Hit the button and bang! the computer went dark and cold. Not only was that a really bad thing when the switch was hit accidentally by your knee, but it also made for some potentially dangerous wiring and frequently made it almost impossible to replace power supplies with soldered connections to the power switch.

Old-timers will recall that the Windows shutdown sequence would end with a screen advising that “it is now safe to shut off your computer.” The power button had to be pressed manually to finish turning off the power.

In 1995, Intel introduced the ATX form factor for computer cases, motherboards, and power supplies and for the first time, Windows could shut off the power to a computer. When you click on Start / Shut down / Shut down in Windows XP, Windows closes all your open programs, shuts down running services, and shuts down Windows, and as its final act it tells the power supply to shut the computer’s power off completely.

vistapower The ATX form factor lends itself to other tricks for low power consumption, leading to a change in Vista: when you click on Vista’s power button, the computer goes to sleep by default instead of shutting down completely. You can get it to shut down or restart from the flyout menu on the right. Here’s some information about Vista’s power management features. If you have trouble with sleep mode, you can change that behavior in Vista’s power options console.

All of that leads to the thrilling conclusion: when you push the power button on your desktop computer case or notebook computer, you’re not directly turning the power on or off. You’re asking the motherboard and the operating system to work with you on whatever they are designed to do.

When the computer is operating normally, pushing the hardware power button in Windows is exactly the same as pushing the onscreen power button. In Windows XP, it starts the normal routine to shut down programs and only then turn off the power. In Windows Vista, it sends the computer to sleep.

If the computer is completely frozen, the motherboard and operating system will not respond to a poke on the power button any more than they will respond to a click on the onscreen Start button. When the power button is held down for 4-10 seconds, though, there is a fallback that will turn off the power regardless of the condition of the operating system or motherboard.

So when you need to shut down and nothing else will work, hold the button down. You’ll feel powerful. When you do this for someone else, don’t give away the secret. They’ll respect you and give you cookies. But don’t do it unless absolutely necessary! Computers should always be shut down gracefully whenever possible.

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