Macintosh Computers w/PCI: Zap PRAM Differences (9/95)

Article Created: 19 July 1995

Article Reviewed/Updated: 26 September 1995

TOPIC -----------------------------------------------------------

This article explains the necessary extra steps you need to perform when

resetting the default video settings for Macintosh computers which have

expansion cards based on Peripheral Component Interconnect (PCI) technology

instead of Nubus technology.

DISCUSSION ------------------------------------------------------

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.

This article was published in the "Information Alley":

Volume II, Issue 9, Page 4

Article Change History:

26 Sep 1995 - Added Info Alley information; updated article.

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