The NVRAM or the non-volatile RAM is a special section of your RAM that is set aside to store certain setting of your Mac. This includes your speaker volume, screen display resolution, time zone settings, and the selection of the startup disk volume. The NVRAM remembers your settings even if your Mac is turned off.
Sometimes my Macbook Pro all of a sudden has no sound anymore. Then you can grab an earphone and plug it in and out and the sound settings of your Macbook have been reseted – or you can try to reset your NVRAM.
If you are encountering problems in these areas such as a wrong time zone even if you have set it to your preferences or a fluctuation in speaker volume, it might be time to reset your NVRAM.
To reset the NVRAM, first shut down your computer. Make sure that you can quickly tap in the Command, Option, P and R keys. It might best to locate these and place your fingers at the ready. Power up your Mac and quickly press Command+Option+P+R simultaneously before the grey startup screen shows. Hold it until you see the computer restart and you hear the startup sound. Once you hear the sound, you can release the four keys.
Your Mac’s NVRAM is now reset.