If you’re troubleshooting your Mac, you’ve probably seen this advice before: reset your NVRAM. Some forum denizens talk about this as a cure-all solution to Mac instabilities, but what is NVRAM? And what problems can it actually solve?

What Is NVRAM?

Let’s start by explaining what, exactly, NVRAM does. If you mute your Mac’s volume, then restart it, you won’t hear the iconic startup sound. How does your Mac pull that off? Because volume settings are stored in the NVRAM, which the Mac’s firmware has access to even before macOS begins booting. According to Apple’s official instructions, the NVRAM also stores things like screen resolution, time zone information, and, crucially, which hard drive to boot from.

This is all useful information for your system to have before it boots, but in some cases corrupt NVRAM can cause Mac glitches or even prevent macOS from starting. If you’re having trouble starting up your Mac, briefly seeing a question mark during boot, or finding that your Mac constantly boots from the wrong hard drive, clearing the NVRAM can help. It won’t fix everything, but it doesn’t generally hurt to try—though you may need to reset your time zone, resolution, or other settings like that if you’re using custom ones.

How to Reset Your NVRAM

If you want to reset your NVRAM, there are two main methods. The first (and most reliable) method starts with shutting down your computer. Next, hit the power button. As soon as you hear the startup sound, press and hold the Command, Option, P, and R keys together.

Hold the keys down. Eventually your Mac will restart, and you’ll hear the startup sound again. Feel free to let go of the keys when that happens. The NVRAM should be reset and your computer should start up normally.

If you own a late 2016 MacBook Pro (and presumably other Macs made since then) things work a little differently. Apple killed their classic startup sound, so you won’t hear it. Instead, just hit the keyboard shortcut right after turning on the Mac, then hold those keys for 20 seconds. Your NVRAM should be reset.

How to See What’s In Your NVRAM

Curious about what’s actually in your NVRAM? Open up the Terminal in macOS, which you’ll find in Applications > Utilities. Type nvram -xp, then press Enter. You’ll see the complete contents of your NVRAM.

Don’t expect this to make for great reading. You’ll recognize a few things, like volume levels (pictured above), but you’ll also see a bunch of cryptic keys. What’s here will vary a lot depending on what kind of Mac you have, and other details about your device.

While we’ve got the Terminal open, it’s also possible to clear the NVRAM from here, with the command nvram -c. You’ll need to restart your Mac for the reset to complete, which is why the keyboard shortcut method above is generally considered a better bet.

Clearing your NVRAM won’t solve all of your Mac’s problems, but it can solve some, particularly if you’re having trouble getting your Mac to boot. It’s also possibly a good idea if you’re having issues with your volume or screen resolution settings.

Photo credits: Christoph Bauer, EricRobson214