Technical Q&A QA1103

Resetting NVRAM to factory defaults

Q: I want to reset NVRAM to factory defaults. How do I do that?

A: When you start a Macintosh computer you can reset the configuration variables by holding down the following keys, "command-option-p-r", without the quotes. Listen for the second boot beep before releasing the keys and the configuration variables will be reset. When a Macintosh computer starts, control is immediately given to what Apple terms "Hardware Init". This firmware is contained in ROM and must use the microprocessor registers since memory is not tested and initialized. When you hear the boot beep Hardware Init is finished testing and initializing memory and the microprocessor and passes control to Open Firmware. Open Firmware checks for keys being pressed. In this case, command-option-p-r, is detected and Open Firmware resets NVRAM and then passes control back to Hardware Init which will generate another boot beep. Don't worry if you hold down the keys too long and hear more than two boot beeps. More than two boot beeps will just reenter the startup sequence more times which will not cause any harm.

[Dec 21 2001]