Microsoft KB Archive/52156

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How to Reset the Parameter RAM of a Macintosh



Zapping the Parameter RAM (PRAM) of a Macintosh is one technique for solving various system and application problems on a Macintosh. It is performed at restart time and involves a simple keystroke-combination. Once it is done, many of your settings for Control Panel devices will be reset to their default values.

The parameters (PRAM) of a Macintosh keep track of various settings in the Control Panel, such as General, Mouse and Keyboard. "Zapping," or resetting, the PRAM returns the above files to their default settings.

Zapping the parameters of a Macintosh should only be used as a last resort solution for unusual System behavior. Always first try reinstalling the System and programs or booting up with a floppy System disk and rebuilding the desktop.


To zap the parameters of a Macintosh, do the following:

System 7.0 and later:

  1. From the Special menu, choose Restart
  2. After you release the mouse button, hold down the following keys on the keyboard: COMMAND+OPTION+P+R and continue to hold them down until your hear the second startup sound.

If you don't hear a startup sound, then wait until your screen displays black for the second time, and then release the keys.

System 6.0 and earlier:

  1. Hold down the COMMAND+OPTION+SHIFT keys as you choose Control Panels from the Apple Menu

For more information about zapping the PRAM, see the "Items to be Reset after Zapping PRAM" section below.


The PRAM on a Macintosh is a small, battery powered, piece of RAM. It is powered by an internal battery so that the settings that are stored in PRAM are preserved even when your machine is turned off. These settings are stored in PRAM, instead in a file on disk, so that when you boot off of a different System disk, the settings remain the same. Most of the settings that are stored in PRAM are those that you have selected using Control Panel devices in your System:Control Panels folder (such as whether you are using color or grays, an option set by using the Monitors Control Panel device). When you turn on your Macintosh, the settings that are stored in the PRAM are then read into the main RAM on your Macintosh.

Items to be Reset after Zapping PRAM

After Zapping your PRAM, you may need to reset some of the Control Panel device settings on your machine. The following is a list of some of the more important Control Panel device settings that should be changed after zapping your PRAM. The actual changes to your PRAM settings will vary somewhat, depending on the version of the System software that you are using, and on your computer model.

  1. Memory: Cache Size

Virtual Memory
32-Bit Addressing
RAM Disk

  1. Monitors: Color (on most older Macintosh computers, you will be set back to Black/White)
  2. Network: Zapping the PRAM sets your network back to LocalTalk

Additional query words: 6.0 7.0 parameter noupd

Keywords : kbtshoot
Issue type : kbhowto
Technology :

Last Reviewed: November 24, 1999
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