The difference between NVRAM and PRAM is mostly superficial. The older PRAM used a small dedicated battery to keep the RAM power up at all times, even when the Mac was disconnected from power. The newer NVRAM uses a type of RAM similar to the flash-based storage used in SSDs to store the parameter information without the need for a battery to keep it safe. Aside from the type of RAM used, and the name change, both serve the same function of storing important information your Mac needs when it boots up or accesses various services.
What’s Stored in the NVRAM or PRAM?
Most Mac users don’t think much about their Mac’s parameter RAM, but it works hard anyway, keeping track of the following:
Startup volume Speaker volume Display settings (resolution, color depth, refresh rate, number of displays) Kernel panics information DVD region settings Date and time, including time zone Computer name Backlight levels Keyboard language Location services state (enabled or disabled)
When your Mac starts up, it checks the parameter RAM to see which volume to boot from and how to set other important parameters. Occasionally, the data stored in the parameter RAM is bad, which can cause various issues with your Mac, including the following common problems:
Wrong date, time, or time zone. Speaker volume set too loud or too soft. Display problems. Sometimes you’ll see the gray Apple boot screen and then the display will go blank. Other times you’ll see a message that the resolution or refresh rate is out of range. Wrong startup volume. A question mark (?) at startup, followed by a long delay before your Mac starts up.
How Does the Parameter RAM Go Bad?
Luckily, the Parameter RAM doesn’t actually go bad; it’s just the data it contains that becomes corrupt. There are a number of ways this can happen. One common cause is a dead or dying battery in those Macs that use PRAM, which is a small-button style battery in the Mac. Another cause is your Mac freezing or temporarily losing power in the middle of a software update. Things can also go awry when you upgrade your Mac with new hardware, add memory, install a new graphics card, or change startup volumes. All of these activities can write new data to the parameter RAM. Writing data to the parameter RAM isn’t an issue in itself, but it can be a source of problems when you change multiple items on your Mac. For instance, if you install new RAM and then remove a RAM stick because it’s bad, the parameter RAM may store the wrong memory configuration. Likewise, if you select a startup volume and then later physically remove that drive, the parameter RAM may retain the wrong startup volume information.
Resetting the Parameter RAM
One easy fix for many issues is to simply reset the parameter RAM to its default state. This will cause some data to be lost, specifically the date, the time, and the startup volume selection. Luckily, you can easily correct these settings using your Mac’s System Preferences. The steps needed to reset the parameter RAM are the same, regardless of whether your Mac uses NVRAM or PRAM.
Resetting the NVRAM on Late 2016 MacBook Pros and Later
MacBook Pro models introduced in late 2016 have a slightly different process for resetting the NVRAM to its default values. While you still hold down the usual four keys, you no longer have to wait for a second reboot or listen carefully to the startup chimes.
Alternative Method to Reset the NVRAM
There is another method for resetting the NVRAM on your Mac. To use this method you must be able to boot your Mac and log in. Once the desktop is displayed perform the following:
After Resetting the PRAM or NVRAM
Once your Mac finishes starting, you can use the System Preferences to set the time zone, set the date and time, select the startup volume, and configure any display options you wish to use. To do this, click the System Preferences icon in the Dock. In the System section of the System Preferences window, click the Date & Time icon to set the time zone, date, and time, and click the Startup Disk icon to select a startup disk. To configure display options, click the Displays icon in the Hardware section of the System Preferences window. Still having problems? Try resetting the SMC or running the Apple Hardware Test.
