Resetting your Mac's PRAM and NVRAM
Summary
This document explains how to reset the parameter random access memory (PRAM) and nonvolatile RAM (NVRAM) on Macintosh computers.
Important: If your computer does not retain parameter RAM (PRAM) settings when it is turned off, this generally indicates that the battery needs to be changed. Refer to Macintosh Family: Batteries and Part Numbers.
Products Affected
Portable Computers, Desktop Computers
Resetting PRAM and NVRAM
- Shut down the computer.
- 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 Command-Option-P-R keys. You must press this key combination 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.
Your computer's PRAM and the NVRAM are reset to the default values. The clock settings may be reset to a default date on some models.
Resetting PMU on PowerBook or iBook computers
In some troubleshooting situations, if resetting PRAM does not resolve an issue, resetting the PMU may be the next appropriate step. For information on when this is appropriate and for instructions on how to reset the PMU in your PowerBook computer, see Resetting PowerBook and iBook Power Management Unit (PMU).
Additional Information
Resetting NVRAM in Open Firmware
If your computer is Open Firmware-based (Power PC) and you are unable to reset NVRAM as described above, you may alternatively reset the NVRAM and Open Firmware settings using the steps in the Solution section of Message “To continue booting, type 'mac-boot' and press return”.
In some cases, an Open Firmware-based computer may not respond to the keyboard commands noted above, and may not allow starting up into Open Firmware by pressing and holding the Command, Option, O, and F keys during startup. If you are unable to get to an Open Firmware prompt (and your computer supports doing so), try powering on the computer with the power button held down continuously—as if you were doing a firmware update. This should force the computer into Open Firmware, allowing the steps in the article noted above to be used.
Contents of PRAM
Some Macintosh computers may not have all the settings described below. For Mac OS X information, refer to Mac OS X: What's Stored in PRAM?
- Status of AppleTalk
- Serial Port Configuration and Port definition
- Alarm clock setting
- Application font
- Serial printer location
- Autokey rate
- Autokey delay
- Speaker volume
- Attention (beep) sound
- Double-click time
- Caret blink time (insertion point rate)
- Mouse scaling (mouse speed)
- Startup disk
- Menu blink count
- Monitor depth
- 32-bit addressing
- Virtual memory
- RAM disk
- Disk cache