Detailed Information for the
Non Volatile Memory Chips Inside Apple Computers.

Please read the nvRAM Executive Summary first.

The information that is stored in these chips is critically important.
Sometimes they get corrupted and must be re-set with secret and obscure key sequences.

PMU = SMC = SMU • • • nvRAM = pRAM = Open Firmware • • • rEFIt & EFI

The
Power Management Unit
and
System Management Controller
and
System Management Unit
(PMU = SMC = SMU)

• What they manage:
  - Controls the sleep, wake, startup, shutdown and hibernate modes and other battery related operations.
  
• To lookup what Mac you have, try www.everymac.com .

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  - To RESET IT on a Intel CPU that has a BUILT-IN battery do,
  
  
  1. Shut down the computer.
  2. Plug in the power adapter.
  3. Press and HOLD the (left side) Shift-Control-Option(ALT) keys AND the power button all at the same time.
  4. Release all the keys AND the power button at the same time.
  
  - You are DONE ! You can now press the power button and turn your computer back on.

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  - To RESET IT on a Intel CPU (and newer PPC's) do,
  
  
  1. Shut down the computer.
  2. Disconnect the AC Adapter.
  3. Remove the battery (if it is a laptop).
  4. Press and hold the power button down for 5 seconds.
  
  - You are DONE ! You can now press the power button and turn your computer back on.
  (don't forget to put the laptop battery back in, ok?)

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  - To RESET it on very old PPC CPU's,
  
  
  1. Shut down the computer.
  2. Press the Shift-Control-Option-Power.
  
  - You are DONE ! You can now press the power button and turn your computer back on.
  • You will know it was done by looking at sudo dmesg |grep "CLOCK RESET"
    or, watching for the message below if you are running in VERBOSE MODE.
    ApplePMU::CLOCK RESET! PMU WAS PROBABLY RESET SOMEHOW!!
  • If you hear a large tone and the front LED blinks, let go of the keys IMMEDIATELY,
    or you will be dumped down into the Open Firmware terminal....
    
  • This will happen if you are using the wrong trick to reset the PMU.
    - Use the power button trick above.
    
  • Don't panic if you get dumped into the Open Firmware terminal.
    - Just type mac-boot and hit return.

The
Parameter Random Access Memory
(PRAM = Open Firmware = nvram)

What it manages:

- The MOST important item which can be set here is what "boot-device" we boot up.
- The second most important item which can be set here is the boot-args, see VERBOSE MODE.
- A "oem-logo" can be set here.
- A "oem-banner" can be set here.
- More too, see below !

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- To RESET it,

• Start this with the power off then hold down the keys below, and turn the power back on.
  
• Command (apple) + Option (alt) + P + R
  
• Wait for boot chime.
  
  
• This should be done a few (3~5) times in a row, just keep holding down the keys.
  
• This will NOT work if you have a in your Open Firmware.
  
• You will know it was reset by looking at (see above) DMESG for the string,
  ApplePMU::CLOCK RESET! PMU WAS PROBABLY RESET SOMEHOW!!
  
• This is often refered to as "zapping PRAM" or "zapping the PRAM"...

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  Cool things you can set in the Open Firmware nvRAM chip.

  1. Put your system into VERBOSE MODE,
     so you can see all the cool boot items instead of the silly splash screen.
     
     
  2. You can Password protect it.
     
     
  3. Want to hide your name in it ?
     sudo /usr/sbin/nvram oem-banner="I belong to Gary Sullivan"
     
     
  4. And since the NVRAM can hold stuff, why not put your OWN stuff it in.
     - To add,
     sudo /usr/sbin/nvram fart-face="Not Me Dude"
     
     - To remove,
     sudo /usr/sbin/nvram -d fart-face
     
     
  5. To see what's currently in it, do:
     /usr/sbin/nvram -p |more
     
     
  6. Do a ONE TIME ONLY boot into Target (FireWire) Mode on a Intel Only system, do:
     sudo /usr/sbin/nvram target-mode=1
     
     
  7. And to be sure the most dangerous of all the things you can mess up,
     - go into the Open Firmware "terminal" on a PPC based system.
     
     • To do this, at power up, hold down the keys, Command (apple) + Option (alt) + O + F
       - all at the SAME time and let go after CHIME.
       
     • To exit, just type mac-boot and hit return.
     
     
     
  Back to the TOP.

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  PLEASE do not panic if your system seems to "hang" after you see the line below while booting in VERBOSE MODE, or in the dmesg messages seen below.
  [HCIController][configurePM] power parent ready after 1 tries Just wait as long as 10 human min for the poor old Kernel to finish rebuilding...
  
  This is why I realy wish Apple would add a HDD LED (LAN LED too while you are at it) on ALL it's computers...

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  Now to confuse the heck out of you.
  The rEFIt, EFI shell
  
  
  
  AKA, The Secret Hidden System Boot Partition Manager

  ---

  The EFI "firmware" is a boot-loader which points to and runs the boot file called:
  /System/Library/CoreServices/boot.efi .
  

  ---

  - Compaired to a WindowZ box it is kinda-sorta like having all the Hidden, System Read only files like,
  
  AUTOEXEC.BAT, boot.ini, ntldr, MSDOS.SYS, IO.SYS, CONFIG.SYS and NTDETECT.COM (the BIOS & MBR too)
  
  all rolled into one function.
  

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  - Only INTEL based Mac's have the abilty to use the EFI "shell".
  - This shell is NOT installed by default.
  - This is NOT Apples "Boot Camp".

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• It is a disk BOOT manager.
• It is a disk partition manager.
• It can be used to make your Mac MULTI-BOOT.
  
• Perform at your own risk, but when you do hose your system remember,
  - Power off your system.
  - Wait 10 seconds.
  - Hold down the power button as you plug it back in.
  - Now boot from the restore DVD etc.
  

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• To get the rEFIt boot manager, goto http://refit.sourceforge.net/,
  and make your own stand alone BOOTABLE CD....
  
  
• For more info on it see,
  http://efi-shell.tianocore.org/
  and or
  http://www.tianocore.org/
  - Intel gave it to TianoCore by the way.
  
• Nice FAQ over at Life Hacker (subset of GizmodO).

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© Gary Sullivan Maintainer of this page. The URL of this page is: http://www.hackerskitchen.com/mac-old/nvram-detailed.html Constructive Comments, Suggestions and Requests are welcome.

™