In Mac OS and Mac OS X, what is the PRAM, and why would I want to zap it?

In a Mac OS or Mac OS X computer, the parameter RAM (PRAM) and non-volatile RAM (NVRAM) are small amounts of RAM that store certain settings. PRAM and NVRAM are not cleared when you turn off your computer's power; they are kept active by a battery or capacitor on the motherboard.

Occasionally, the PRAM can become corrupt and cause problems on your computer. If you're experiencing problems you've been unable to troubleshoot, you can sometimes solve them by "zapping" the PRAM. To do so:

1. Hold down the Command, Option,  p , and  r  keys while starting or restarting your computer. This will automatically restart your computer a few seconds after it powers on.
   
   
2. Keep holding down the Command, Option,  p , and  r  keys, and allow your computer to restart seven times. After the seventh time, let your computer power up and boot normally.
   
   
3. You may need to restore some of your settings that have been reset to factory defaults.

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