2012.06 Article: Resetting PRAM and Repairing Disk Permissions

By Holly McEntee

PRAM stands for "Parameter Random Access Memory" and is pronounced "pea-ram". PRAM is a type of memory found in Macintosh computers that stores system settings. These settings include display settings (like screen resolution and color depth), the time-zone setting, speaker volume, and the startup volume choice. The system settings that are stored in the computer's PRAM differ from Mac to Mac, but the purpose of the memory remains the same. When something goes wrong, a technician may ask if you've reset the PRAM, because resetting the defaults is like throwing a large net over small problems to make sure the problem isn't a simple issue before delving into the internals of the unit.

Resetting defaults is not a sure-fire cure-all. However, it is free and an easy way of possibly fixing the issue (ranking right up there with repairing disk permissions). So, it is definitely worth a shot.

How to reset the PRAM:
  1. Shut down the computer.
  2. Locate the following four keys on the keyboard: Command (⌘), Option, P, and R. You will need to hold these keys down simultaneously in Step 4.
  3. Turn on the computer.
  4. Press and hold the Command-Option-P-R keys. You must press this key combination before the gray screen appears.
  5. Hold the keys down until the computer restarts and you hear the startup sound for the second time.
  6. Release the keys.
If you choose to reset your PRAM, you may need to set your display, time zone, startup volume, and other affected settings using System Preferences (accessible under the  menu). Some firmware updates may reset your PRAM as part of their installation process, which will means you will have to reset the affected settings after the installation.

Many programs you install on your Macintosh in OS X are package files (.pkg), each of which contains a file or files with the extension .bom (standing for, quaintly, bill of materials). This little .bom file contains a list of permissions, "rules" that control your ability to view or make changes to the contents of the file. Occasionally in OS X some key file ownership and permissions get changed for whatever reason by applications and more frequently, program installers. When ownership and permissions get changed, things just don't work as they should. The symptoms might be programs quitting unexpectedly, preferences not being remembered, programs not launching, etc.

If you notice these types of problems, one very easy diagnostic procedure you can perform is to Repair Disk Permissions. (Plus it makes you sound smart to say off-handedly to the guy at the Genius Bar "Oh, sure, I repaired the disk permissions, but it didn't seem to help" ... especially if you can combine this with the previous article and add nonchalantly "I even reset the PRAM.").

Repair Disk Permissions is a Mac OS X utility, which is part of the Apple Disk Utility program. It corrects the ownership and permissions according to Apple specifications. Frequently, this corrects many system and program errors. To Repair Disk Permissions, follow these steps:
  1. Open the Disk Utility program found in the Applications > Utilities folder on your hard drive.
  2. Click on the "First Aid" tab in the window that opens.
  3. In the list to the left, click once on the icon/name of your hard drive to select it as the disk whose permissions need repairing.
  4. Click on the button labeled "Repair Disk Permissions". (Why not "Verify Disk Permissions"? Because "Repair" verifies them anyway, then goes ahead and fixes them.)
  5. The repair process begins, and may take several minutes. This is normal. (Do not be intimidated by a progress bar indicating you have hours left to go. It's lying.)
  6. After the repair is done you will see a long (or short) list of files that were repaired. You need not study this or write it down. If you want to print it to a PDF and save it for future reference, do so.
  7. Quit Disk Utility.
You may not notice any immediate or obvious changes or improvement, but then again you might. Repairing Disk Permission is less necessary with systems since OS X 10.5, but it won't hurt. If you install a lot of programs (especially through Software Update) it's generally recommended you run Repair Disk Permissions every other month or so in the name of good general maintenance.

(Editor's note: See diagrams of the process.)


  1. I have to replace a hard drive for my imac.
    But when I went to the apple store they said it would cot $428
    The hard drive itself costs under 100
    I don't want to pay over 300 for just labor.
    mac repairs

  2. Good blog! I have found here much useful information for yourself and would like to thank you for done by work.

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