PRAM and Zapping the PRAM
Zap the PRAM sounds like a character out of Douglas Adams’s Hitchhiker’s Guide to the Galaxy. It isn’t, though; PRAM is a component inside your Mac’s case that remembers stuff like how loud your speakers should be when the computer chimes and what startup disk to choose. The PRAM (stands for parameter RAM) is a small portion of RAM that remembers what time it is and similar system data.
PRAM is powered by a battery. Because it’s powered by battery it remembers this information even when the computer is turned off. If the PRAM becomes corrupt, all kinds of things can go wrong, including failure of the system to boot properly or the system not booting at all. You’ll recognize PRAM problems when the time and date are wrong, if the color scheme is wrong, or if you can’t print or connect to the Internet for unknown reasons.
I think you should zap your PRAM once a year, just to make sure it hasn’t become corrupt, or whenever the computer starts to behave strangely. Zapping the PRAM is easy (and safe, don’t be scared) and part of your Mac maintenance:
1. From the Apple menu, choose Restart.
2. Hold down the Command+Option+P+R keys.
3. The computer will restart, at which point you can let go of those keys.
Tip: Once you zap the PRAM, you may have to reset system data like the date and time and the default startup disk.