iMac (21.5-inch, Late 2009) — General Troubleshooting 20
2010-11-18
Resetting Parameter RAM (PRAM)
PRAM stores certain system and device settings in a location that Mac OS X can access quickly.
Exactly which settings are stored in the computer’s PRAM varies depending on the type of
computer as well as the types of devices and drives connected. To reset PRAM:
1. Shut down the computer.
2. Locate the following keys on keyboard: Command, Option, P, and R. You will need to hold
these keys down simultaneously in Step 4.
Note: If the keyboard does not have an Option key, use the Alt key instead.
3. Press power button.
4. Immediately press and hold Command-Option-P-R keys.
Important: You must press this key combination before the gray screen appears.
5. Hold down keys until the computer restarts, and you hear the startup chime a second time.
6. Release keys.
For more information, refer to:
kBase #HT1242: Mac OS X: What’s stored in PRAM
kBase #HT1379: Resetting your Mac’s PRAM and NVRAM
Starting Up in Safe Mode
Starting up into Safe Mode does several things that can help resolve software or directory
issues that may exist on the startup volume. To start up in Safe Mode:
1. Shut down the computer.
2. Press power button.
3. Immediately after you hear startup tone, press and hold Shift key.
Note: The Shift key should be held as soon as possible after startup tone but not before.
4. Release Shift key when you see the screen with a gray Apple and progress indicator (looks
like a spinning gear). Note that booting into Safe Mode will take longer than a normal
startup. During startup, the words ”Safe Boot” will appear on Mac OS X startup screen.
5. To leave Safe Mode, restart computer normally, without holding down any keys during
startup.
For more information, refer to:
kBase #HT1564: Mac OS X: What is Safe Boot, Safe Mode?
kBase #TS1884: Safe Boot takes longer than normal startup
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