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Reset the PRAM And NVRAM on a Macintosh

Reset the PRAM


* What is PRAM?
* Zapping the PRAM
* Other Tools and Info

What is PRAM?

Parameter RAM (PRAM) is a private playground for Apple engineers. Some of the contents of this battery-backed memory are documented, but most remain a mysterious secret. That may be acceptable when everything works correctly, but PRAM has been implicated in various crashes and installation problems. PRAM stores various pieces of information that the Macintosh would like to remember when it is turned off or unplugged. This includes:

* Desktop Pattern
* Date
* Highlight color
* keyboard settings
* Map settings
* Memory settings
* Mouse speed
* Network settings
* PowerBook Power Management
* Sound settings
* Startup disk
* Time
* Other undocumented and system-spefic information

Zapping the PRAM

"Zapping PRAM" is a way of resetting PRAM back to its original factory values. The basic procedure is to hold down a special combination of keys: Command-Option-P-R while powering on the Macintosh and waiting for the start-up sound. The latest recommendation from Apple requires holding down the keys until the start-up sound has repeated three more times. (Avoid holding down the power key too long because this reportedly triggers a problem on certain Macs, in which a ROM-based debugger dialog appears unexpectedly on the screen at a later time. You can type "G" to make the processor "Go" ahead from its suspended debugging state and continue operating normally.)

Two ways to reset Macintosh PRAM

  • 1) Holding down the following keys as the system is booting: [Command] [Option] p r
  • 2) Use TechTool Lite
    This free utility from MicroMat--makers of TechTool Pro--does a very good job of helping you reset your PRAM. It even offers you a way to save your previous PRAM settings if you ever want to revert

After resetting PRAM, check Chooser settings and Control Panels settings, including Color, Keyboard, Mouse, General Controls, Memory, Network, Sound and Startup Disk. With PowerBooks, check the various power-management options, too.

The most thorough, and most difficult, way to reset PRAM is by removing the computer's power cord and the battery on the motherboard that powers PRAM in the absence of normal power. Pushing the power switch a few times and waiting for a half-hour or more should flush everything out, including things you may prefer to retain, such as manufacture date, the number of power-on hours, and the date and time settings. (If the battery that backs up PRAM runs low, all sorts of bizarre problems can occur on the system, and the battery must be replaced. One typical symptom is that the Mac clock changes to strange values between the Mac's zero date of Jan. 1, 1904 and the current date.)

Resetting NVRAM

Resetting the NVRAM will resolve many issues. If done correctly, it should not damage any aspect of your computer.

Two ways to reset Macintosh NVRAM

  • 1) Holding down the following keys as the system is booting: [Command] [Option] n v
  • 2) Via Open Firmware - does not reset PRAM, according to Apple. To do so:

* Hold down the following keys as the system is booting: [Command] [Option] o f
* You will be presented with a gray screen with a command prompt.
* Enter the following Open Firmware commands, followed by [Return], in order:


This article explains the steps required when resetting the Parameter RAM (PRAM) or Non-volatile RAM (NVRAM) on Macintosh computers.

Resetting PRAM On Non-PCI Power Macintosh Computers

System 6.x

  • 1. While opening up the Control Panel, hold down these keys: Command, Option, Shift.
  • 2. A dialog appears asking if you want to clear parameter RAM; select Yes. A few seconds later, the Control Panel opens.
  • 3. Close the control panel.
  • 4. Restart your computer.

Parameter RAM is reset, however the clock is not reset. Restarting is necessary to complete this operation. After restarting your computer, you can reset your options through the control panel.

System 7.x
IMPORTANT: These steps do not apply to the PowerBook 5300, PowerBook 190, PowerBook 1400, or PCI-based Power Macintosh computers. See sections below for applicable steps for these computers.

  • 1. Locate the following keys on your keyboard - Command, Option, "P", and "R". You will need to hold these keys down simultaneously in step 2.
  • 2. Restart your Macintosh and hold down the Command-Option-"P"-"R" key combination. You must press this key combination before the "Welcome to Macintosh" screen appears.
  • 3. Hold the keys down until the Macintosh restarts itself twice.
  • 4. Release the keys after the Macintosh restarts twice.

Your parameter RAM in your Macintosh is reset to the default values. The clock setting are not changed.

For more information on parameter RAM, search the Tech Info Library under "PRAM".

PowerBook 5300,190 6 1400: Resetting PRAM

Resetting ("Zapping") the Parameter RAM (PRAM) when the computer is shut down also resets the power manager.

  • 1. Shutdown the PowerBook, not restart.
  • 2. Turn the PowerBook on and hold down the all of the following keys at the same time: Command-Option-P-R keys.
  • 3. There will be only a single chime, then the screen will go dark and the green sleep light will be on solid. NOTE: The chimes may reoccur once or they may reoccur and then the screen goes dark.
  • 4. Press the Reset button one more time and the PowerBook starts after a brief pause. NOTE: If the PowerBook powers off and the sleep display light stays a solid green - no blinking, press the reset button once.
  • 5. If the PowerBook does not turn on from the Reset button, turn the PowerBook on by pressing the Power-On key in the upper right corner of the keyboard.

Resetting PRAM And NVRAM On PCI Power Macintosh Computers

In Macintosh computers that have expansion cards based on NuBus technology, holding down the Command-Option-P-R keys simultaneously at startup erases the Parameter RAM (commonly called Zapping the PRAM). This resets the machine to its default configuration settings.

One of the things resetting the PRAM does is to force the display to startup in its default configuration, all the way through the startup process. The Display Manager in NuBus-based Macintosh computers recognizes that the PRAM has been cleared, therefore, it would not try to restore the display to its previous resolution.

However, in Macintosh computers that have expansion cards based on PCI technology, the display information is not kept in PRAM. It is stored in Non-volatile RAM (NVRAM).

NVRAM can be cleared by holding down the Command-Option-P-R keys simultaneously as soon as possible after hitting the power-on key. It happens BEFORE you see the gray screen. Once the gray screen appears, the PRAM is cleared at the same point as it was in previous machines.

One very important difference is that NVRAM is not cleared during a warm or soft restart (by selecting Restart from the Special menu), whereas PRAM is cleared in that case.

Other Tools and Info

A freeware utility called TechTool, from MicroMat Computer Systems, offers a much neater alternative to electrical tricks. TechTool claims to thoroughly clear all of PRAM after saving important settings to a file on disk. The utility also provides a button for rebuilding the Mac's invisible desktop files, and it lists many details about the system's operating system and hardware. TechTool 1.0.6 is available from standard freeware sources, and you can reach MicroMat at

Matthias Wuttke's PRAM-Reader 1.2 is also freeware. PRAM-Reader simply saves the full contents of PRAM to a disk file or restores PRAM from the file. It is useful for saving a clean copy of your settings after you go through the lengthy process of clearing PRAM and reconfiguring everything. Once you have the file, you can quickly restore from it whenever a PRAM problem is suspected. Source code is available from Wuttke at

A special quirk of PRAM in the Macintosh 630 models requires an additional step when zapping the PRAM. In these Macs, one is supposed to push "a red button near the SCSI connector on the logic board" whenever the logic board is removed and replaced.

When swapping NuBus cards in any Mac, it may be important to clear some data out of a special NuBus settings PRAM. Remove NuBus cards and power up the computer once before installing the new card configuration.

Some tool hosted at Gambas Mac Page

Pram Battery Checker 1.0.2 application
PramInspector 1.1 application
PRAM-Reader V1.2 (fat) application
ParamRAM guard
PRAM Auto-Restore 1.0 control panel
PramSet 1.1 control panel
ForcePRAM includes PRAMSpy application

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