How to reset the PRAM or PMU

Reset NVRAM / PRAM

Mac OS X stores only six things in PRAM: If you're resetting PRAM in an attempt to resolve other issues in Mac OS X, you're using the wrong technique. For more information see HT1379 About NVRAM and PRAM.
 
Here's how to do it: Press and hold on start up ⌥ ⌘ P R

Reset SMC / PMU

A computer's SMC (System Management Controller) used to be the PMU (Power Management Unit) in PB's. Resetting SMC is relevant to: Performing a PMU reset returns the iBook and PowerBook hardware, including NVRAM, to default settings and forces the computer to shut down. For most situations, a restart is sufficient. If the computer has stopped responding, try these steps, in order, until the computer responds:
  1. Force Quit (⌥ ⌘ esc)
  2. Restart (ctrl ⌘ Power)
  3. Shut Down via menu or Force Shut Down (press the Power button for 10 seconds)
Only perform a PMU reset on the computer if none of the above steps resolved the situation (see HT3964 Resetting the System Management Controller).
 
Here's how to do it:
  1. Shut down the computer.
  2. Plug in the MagSafe power adapter to a power source, connecting it to the Mac if its not already connected.
  3. On the built-in keyboard, press the (left side) ⇧ ctrl ⌥ keys and the Power button at the same time.
  4. Release all the keys and the power button at the same time.
  5. Press the power button to turn on the computer.
For the PowerBook G4, to reset the PMU do this:
  1. If the computer is on, turn it off.
  2. Disconnect the AC Adapter and remove the computer's battery.
  3. Press and hold down the Power button for 5 seconds and then release the button.
  4. Reconnect the battery and AC Adapter.
  5. Press the Power button to restart the computer.
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