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 on the motherboard.

Note: Instead of a battery, the iBook and PowerBook have a capacitor that allows them to maintain settings for up to ten minutes after both AC and battery power have been removed.

Occasionally the PRAM can become corrupt and cause problems with your computer. If you are experiencing problems that have resisted other attempts at troubleshooting, you can sometimes solve them by "zapping" the PRAM. To do so, follow these steps:

1. Hold down the Cmd, 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 Cmd, 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 go in and change some of your settings, as they will be reset to factory defaults.

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