How to Reset PRAM and SMC/PMU

What’s PRAM?

The Parameter RAM is a small amount of “nonvolatile” RAM (NVRAM) that holds various settings that the system can use before the operating system loads, and maintains these settings even when the computer is turned off. There is a small battery on the computer’s mainboard that helps maintain the PRAM settings when power is off.

  • Volume changes or won’t stick.
  • Video resolutions not sticking or not all available
  • Time zone information and clock settings
  • Boot volume isn’t set (question mark shows briefly before booting)
  • Keyboard repeat rates
  • Mouse input rates (click and tracking speeds)

How To Reset PRAM:

To reset the PRAM, reboot the computer and hold the options-command-P-R keys at the same time. The computer will chime, and then continually reset and chime while these keys are held. Allow it to cycle a couple of times and release the keys and allow the computer to boot normally.

NOTE: Resetting the PRAM may require you to set some settings such as mouse speed and keyboard rates again.

What’s SMC/PMU?

The System Management Controller (Intel Macs) or Power Management Unit (PowerPC Macs) is a chip that manages the power for various system components such as the fans and backlights, as well as the circuits that initiates power to the whole system when you turn on your computer.

Like the PRAM, many people readily offer suggestions for resetting the SMC or the PMU. However, there are specific behaviors that will benefit from SMC/PMU resets, and others that won’t. For the most part, the power management in the computer should only be reset if you experience problems with seemingly “stuck” settings, or nonfunctional indicators, especially any on the hardware itself (power adapter indicator, or battery life for laptops). The following list of situations are some instances where a SMC/PMU reset can be beneficial:

  • Battery isn’t charging properly
  • Display brightness won’t work properly
  • Keyboard backlight won’t work
  • Fans blaring all the time
  • Power button not functioning properly
  • Closing/opening laptop lid doesn’t sleep/awaken the computer
  • External ports not receiving power
  • External devices not recognized
  • Internal components such as Airport or Bluetooth not starting up
  • Unexpected shutdown

How To Reset SMC/PMU?

Resetting the SMC/PMU will depend on the machine you have, but here are some resources for a few Mac models:

Mac Pro

iMac and Mac Mini

MacBook and MacBook Pro

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