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Overview
Mac stores certain settings in a special memory area even if it is turned off. On Intel-based Macs, this is stored in memory known as NVRAM; on PowerPC-based Macs, this is stored in memory known as PRAM.
What Is Stored In NVRAM / PRAM
Information stored in NVRAM / PRAM includes:
- Speaker volume
- Screen resolution
- Startup disk selection
- Recent kernel panic information, if any
If you experience issues related to these functions, you may need to reset the NVRAM or PRAM. 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 / PRAM may help.
macOS X does not store network settings in NVRAM / PRAM. If you are troubleshooting a network issue, resetting it will not help.
How To Reset NVRAM / PRAM
- Shut down the Mac.
- Locate the following keys on the keyboard: Command (⌘), Option, P, and R. You will need to hold these keys down simultaneously in step 4.
- Turn on the computer.
- Press and hold the ⌘ + Option + P + R keys before the gray screen appears.
- Hold the keys down until the computer restarts and you hear the startup sound for the second time.
- Release the keys.
After resetting NVRAM or PRAM, you may need to reconfigure your settings for speaker volume, screen resolution, startup disk selection, and 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.