Zapping PRAM on a PCI-Based Macintosh

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By Stephanie Hahn

You need to perform extra steps when resetting the default video settings for Macintosh computers which have expansion cards based on Peripheral Component Interconnect (PCI) technology instead of Nubus technology.

NuBus

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.

PCI

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.

Resetting The Display Defaults

The following steps need to be taken to start up with the default display configuration settings after resetting the PRAM on a PCI-based Macintosh computer:

Step 1: Zap PRAM by holding down the Command-Option-P-R keys simultaneously from a cold startup (that is, you must turn off or shutdown the computer, then turn it back on again; you cannot choose Restart from the Special menu).
Step 2: After the second startup sound, release all of the keys and startup with the extensions off by holding down the Shift key until you see the message that says "Welcome to Macintosh Extensions Off". Then you can release the Shift key.
Step 3: Once the machine has started up, go to the Preferences Folder, which is inside the System Folder, and throw away the Display Preferences file.

This new procedure is needed because of extensive changes to the Display Manager and the new way the display preferences are handled.

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