How to Restart Your Mac
If your Mac is acting sluggish or programs are failing to run, you may need to turn off your computer and restart it. Restarting your Mac essentially clears your computer’s memory and starts it up fresh. When you restart your computer, your Mac closes all running programs and offers to save any files you’re working on. After you choose to save any files, your Mac will finally boot up again.
Restarting a computer isn’t the same as turning the computer on and off, which completely resets the computer. If you really want to make sure that your computer starts up correctly, turn it off, wait a few seconds, and then turn it on again. If you’re in a hurry, try restarting your Mac, and if that doesn’t fix the problem, you’ll have to turn it off and on again.
To restart your computer, you have three choices:
Press the power button (or press Control+Eject) and, when a dialog box appears, click the Restart button.
Choose the Apple key and then click Restart.
Press Control+Command+Eject (or Control+Command+Power button).
Pressing the Control+Command+Eject/Power button is the most reliable way to restart a Mac because it doesn’t rely on the Mac OS X operating system.