how to reset PRAM and NVRAM on a mac

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  • a mac computer, connected to a power source.
  • a keyboard connected to the mac.


  1. shut down the computer.
  2. locate the following keys on the keyboard: Command, Option, P, and R. You will need to hold these keys down simultaneously in step 4.
  3. turn on the computer.
  4. press and hold the Command-Option-P-R keys. You must press this key combination before the gray screen appears.
  5. hold the keys down until the computer restarts and you hear the startup sound for the second time.
  6. release the keys


If your computer does not retain parameter RAM (PRAM) settings when it is turned off, this generally indicates that the *battery needs to be changed (not all macs have such a battery, in some isolated cases you may need to change the whole motherboard).  Please go here to see if your model has such a battery.

Settings kept by PRAM (there may be some models that do not have some of these setting):

  • Status of AppleTalk
  • Serial Port Configuration and Port definition
  • Alarm clock setting
  • Application font
  • Serial printer location
  • Autokey rate
  • Autokey delay
  • Speaker volume
  • Attention (beep) sound
  • Double-click time
  • Caret blink time (insertion point rate)
  • Mouse scaling (mouse speed)
  • Startup disk
  • Menu blink count
  • Monitor depth
  • 32-bit addressing
  • Virtual memory
  • RAM disk
  • Disk cache

More details here.

*battery: a small battery similar to a bios ones from the functionality point of view.

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