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1995-11-02
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81 lines
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.
Support Information Services Copyright 1995, Apple Computer, Inc.
Keywords: kpci,kppc,supt,hts,kalley
==================================================================
This information is from the Apple Technical Information Library.