When to reset NVRAM or PRAM
Summary
Your Mac stores certain settings in a special memory area even if it is turned off (unless there is a battery issue as described below). On Intel-based Macs, this is stored in memory known as NVRAM; on PowerPC-based Macs, this is stored in memory known as PRAM. Information stored in NVRAM or PRAM may include:
- Speaker volume
- Screen resolution
- Startup disk selection
You may need to reset the NVRAM or PRAM if you experience issues related to these functions. For example, if your Mac starts up from a startup disk other than the one you've specified in Startup Disk preferences, or if a "question mark" icon appears briefly when your Mac starts up, resetting NVRAM or PRAM may help.
Products Affected
Mac OS X 10.4, Mac OS X 10.3, Mac OS X 10.2, Mac OS X 10.1, Mac OS X 10.0, Portable Computers, Desktop Computers, Mac OS X 10.5
After resetting NVRAM or PRAM you may need to reconfigure your settings for speaker volume, screen resolution, startup disk selection, time zone information. If issues persist, your Mac's logic board battery (not a portable Mac's rechargeable battery) may need to be replaced. The logic board battery helps retain NVRAM/PRAM settings when your computer is shut down. You can take your Mac to a Mac Genius or Apple Authorized Service Provider to replace the battery on the logic board.
Additional Information
Third-party displays
If you have screen resolution issues with a third-party display (monitor) and resetting the NVRAM/PRAM does not help, try using the display's built-in menu system if it has one. For details, see the manual that came with your monitor. There may be buttons on the front of the display to configure the internal settings and screen geometry. The display may include an "automatic" adjustment mode too.
Tip: If you use a DVI connection and you must click "Detect Displays" (in Display preferences) several times for your third-party display to be recognized, try using the monitor's built in menus to set the DVI connector to a digital signal.