The Parameter RAM, or PRAM, on your Mac is a small amount of non-volatile memory (ie, persistent memory that is not cleared when the power is off) that is used by the system to hold hardware configuration settings such as the audio volume at startup, the default boot disk, and various boot arguments to pass to the default operating system.

Sometimes specific problems your Mac may encounter are a result of corruption in the PRAM, where variables are not stored properly.

In these cases, the system may take a long time to boot as it searches for an appropriate boot volume instead of having a default one to use, or may always boot to Safe Mode or similar mode.

How to Reset

To reset the PRAM on your system, just follow these steps:

1. Restart the computer
2. Immediately hold down the Option-Command-P-R keys after hearing the boot chimes
3. Hold the keys until the system resets and sounds the boot chimes again
4. Release the keys when you hear the boot chimes sound, and allow the system to boot normally

If you continue to hold the keys down in step 3, then if you have a wired keyboard (such as a USB one, or that in a laptop), then the system will continue to receive the instruction to reset the PRAM, and will cycle through resets and restarts until you release the keys.

After Resetting

With the PRAM reset, your system will now populate it with default settings, but sometimes these may not be desired ones. When the OS loads, many such as system audio volume will be reset to stored values in the system preferences; however, to be sure, go to the system preferences and toggle the relevant settings. These include the following:

1. The appropriate boot drive in the Startup Disk system preferences
2. The volume of the system
3. Location services being enabled or disabled (in the Security & Privacy system preferences)
4. Display resolution and brightness
5. iCloud settings
6. Mouse cursor speeds