NVRAM corruption is fairly uncommon, but if your Mac seems to take forever to figure out the correct boot disc, starts up with the wrong screen resolution, or suffers from weird audio problems (like there’s no sound whatsoever or the menu bar’s volume control is grayed out), a reset of the NVRAM might help-and it’s quick and harmless. NVRAM serves approximately the same purpose as PRAM, but instead of storing a dozen or more pieces of information, it now contains just a few: your selected startup disk, speaker volume, screen resolution, time zone, and-if your Mac has crashed recently-details of the last kernel panic. Modern Macs no longer use PRAM they instead use something called NVRAM (NV for non-volatile).