How to Clear the PRAM on a Mac

Resetting the PRAM is a matter of holding down certain keys during startup.

Resetting the PRAM might help if your Mac's display is acting quirky, the computer seems confused about the startup disk, or doesn't seem to be retaining some of the settings it normally retains. The PRAM, or NVRAM in later Macs, stores several user settings when the computer is powered down. For example, the speaker volume is retained for your next start up.

Instructions

1. Shut down the computer.

2. Locate the keys "Command," "Option," the letter "P" and the letter "R" to be prepared for Step 3.

3. Turn on the computer, then quickly press and hold the four keys ("Command," "Option," "P" and "R") simultaneously.

4. Hold all four keys until you hear the computer's startup sound for the second time, then release the keys.

Tips & Warnings

• According to Apple's website, "After resetting NVRAM or PRAM, you may need to reconfigure your settings for speaker volume, screen resolution, startup disk selection, time zone information."

• OSX does not store network settings (as was the case with some older Mac systems). Resetting the NVRAM/PRAM will not correct network issues.

• PRAM stands for "Perimeter Random Access Memory," NVRAM stands for "Non-Volatile Random Access Memory."

• If using an array and the computer will not restart after resetting the PRAM/NVRAM, try holding down "Option" while restarting. Select the startup disk when you see a prompt. Once the computer has started, check "System Preferences" under the Apple menu. Select the "Startup Disk" icon, then highlight the correct startup disk if it is not already highlighted.

• In some instances, such as when using a disk array, resetting the PRAM can cause the system to have trouble starting. See Tips.

References

• Apple Support: When to Reset the NVRAM or PRAM
• Apple Support: Resetting PRAM