TITLE
Macintosh: How to Reset PRAM and NVRAM
Article ID:
Created:
Modified:
2238
6/2/87
9/30/03
TOPIC
This document explains how to reset the parameter random access memory (PRAM) and nonvolatile RAM (NVRAM) on Macintosh computers.
DISCUSSION
Resetting PRAM and NVRAM
1. Shut down the computer.
2. Locate the following keys on the keyboard: Command, Option, P, and R. You will need to hold these keys down simultaneously in step 4.
3. Turn on the computer.
4. Press and hold the Command-Option-P-R keys. You must press this key combination before the gray screen appears.
5. Hold the keys down until the computer restarts and you hear the startup sound for the second time.
6. 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 technical document 14449: "PowerBook and iBook: Resetting Power Management Unit (PMU)".
Additional Information
Resetting NVRAM in Open Firmware
If your computer is Open Firmware-based 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 technical document 42642: "Macintosh: Computer Starts to Text-Based Open Firmware Screen".
Contents of PRAM
Some Macintosh computers may not have all the settings described below. For Mac OS X information, refer to technical document 86194: "Mac OS X: What Is 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
PRAM settings appear to reset after each start up
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 technical document 11751, "Macintosh Family: Batteries and Part Numbers".
