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

In a Mac OS X computer, the parameter RAM (PRAM) and non-volatile RAM (NVRAM) are small amounts of RAM that store certain settings. Turning off your computer's power does not clear PRAM and NVRAM; a battery or capacitor on the motherboard keeps them active.

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. Your computer will automatically restart a few seconds after it powers on.
   
   
2. Keep holding down the Command, Option,  p , and  r  keys, and allow your computer to restart three times. After the third time, let your computer power up and boot normally.
   
   
3. Restore any settings that have been reset to factory defaults.

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