Parameter RAM (PRAM) is a private playground
for Apple engineers. Some of the contents of
this battery-backed memory are documented, but
most remain a mysterious secret. That may be
acceptable when everything works correctly, but
PRAM has been implicated in various crashes and
installation problems. PRAM stores various pieces
of information that the Macintosh would like
to remember when it is turned off or unplugged.
* Desktop Pattern
* Highlight color
* keyboard settings
* Map settings
* Memory settings
* Mouse speed
* Network settings
* PowerBook Power Management
* Sound settings
* Startup disk
* Other undocumented and system-spefic information
Zapping the PRAM
"Zapping PRAM" is a way of resetting
PRAM back to its original factory values. The
basic procedure is to hold down a special combination
of keys: Command-Option-P-R while powering on
the Macintosh and waiting for the start-up sound.
The latest recommendation from Apple requires
holding down the keys until the start-up sound
has repeated three more times. (Avoid holding
down the power key too long because this reportedly
triggers a problem on certain Macs, in which
a ROM-based debugger dialog appears unexpectedly
on the screen at a later time. You can type "G"
to make the processor "Go" ahead from
its suspended debugging state and continue operating
Two ways to reset Macintosh PRAM
1) Holding down the following keys as
the system is booting: [Command] [Option]
2) Use TechTool
This free utility from MicroMat--makers of
TechTool Pro--does a very good job of helping
you reset your PRAM. It even offers you a way
to save your previous PRAM settings if you
ever want to revert
After resetting PRAM, check Chooser settings
and Control Panels settings, including Color,
Keyboard, Mouse, General Controls, Memory, Network,
Sound and Startup Disk. With PowerBooks, check
the various power-management options, too.
The most thorough, and most difficult, way to
reset PRAM is by removing the computer's power
cord and the battery on the motherboard that
powers PRAM in the absence of normal power. Pushing
the power switch a few times and waiting for
a half-hour or more should flush everything out,
including things you may prefer to retain, such
as manufacture date, the number of power-on hours,
and the date and time settings. (If the battery
that backs up PRAM runs low, all sorts of bizarre
problems can occur on the system, and the battery
must be replaced. One typical symptom is that
the Mac clock changes to strange values between
the Mac's zero date of Jan. 1, 1904 and the current
Resetting the NVRAM will resolve many issues.
If done correctly, it should not damage any aspect
of your computer.
Two ways to reset Macintosh NVRAM
1) Holding down the following keys as
the system is booting: [Command] [Option]
2) Via Open Firmware - does not reset PRAM,
according to Apple. To do so:
* Hold down the following keys as the system
is booting: [Command] [Option] o f
* You will be presented with a gray screen with
a command prompt.
* Enter the following Open Firmware commands,
followed by [Return], in order:
This article explains the steps required when
resetting the Parameter RAM (PRAM) or Non-volatile
RAM (NVRAM) on Macintosh computers.
Resetting PRAM On Non-PCI Power Macintosh Computers
1. While opening up the Control Panel,
hold down these keys: Command, Option, Shift.
2. A dialog appears asking if you want to
clear parameter RAM; select Yes. A few seconds
later, the Control Panel opens.
3. Close the control panel.
4. Restart your computer.
Parameter RAM is reset, however the clock is
not reset. Restarting is necessary to complete
this operation. After restarting your computer,
you can reset your options through the control
IMPORTANT: These steps do not apply to the PowerBook
5300, PowerBook 190, PowerBook 1400, or PCI-based
Power Macintosh computers. See sections below
for applicable steps for these computers.
1. Locate the following keys on your keyboard
- Command, Option, "P", and "R".
You will need to hold these keys down simultaneously
in step 2.
2. Restart your Macintosh and hold down the
combination. You must press this key combination
before the "Welcome to Macintosh"
3. Hold the keys down until the Macintosh
restarts itself twice.
4. Release the keys after the Macintosh restarts
Your parameter RAM in your Macintosh is reset
to the default values. The clock setting are
For more information on parameter RAM, search
the Tech Info Library under "PRAM".
PowerBook 5300,190 6 1400: Resetting
Resetting ("Zapping") the Parameter
RAM (PRAM) when the computer is shut down also
resets the power manager.
1. Shutdown the PowerBook, not restart.
2. Turn the PowerBook on and hold down the
all of the following keys at the same time:
3. There will be only a single chime, then
the screen will go dark and the green sleep
light will be on solid. NOTE: The chimes may
reoccur once or they may reoccur and then the
screen goes dark.
4. Press the Reset button one more time and
the PowerBook starts after a brief pause. NOTE:
If the PowerBook powers off and the sleep display
light stays a solid green - no blinking, press
the reset button once.
5. If the PowerBook does not turn on from
the Reset button, turn the PowerBook on by
pressing the Power-On key in the upper right
corner of the keyboard.
Resetting PRAM And NVRAM On PCI Power
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
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.
However, 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
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.
Other Tools and Info
A freeware utility called TechTool, from MicroMat
Computer Systems, offers a much neater alternative
to electrical tricks. TechTool claims to thoroughly
clear all of PRAM after saving important settings
to a file on disk. The utility also provides
a button for rebuilding the Mac's invisible desktop
files, and it lists many details about the system's
operating system and hardware. TechTool 1.0.6
is available from standard freeware sources,
and you can reach MicroMat at email@example.com.
Matthias Wuttke's PRAM-Reader
1.2 is also freeware. PRAM-Reader simply
saves the full contents of PRAM to a disk file
or restores PRAM from the file. It is useful
for saving a clean copy of your settings after
you go through the lengthy process of clearing
PRAM and reconfiguring everything. Once you
have the file, you can quickly restore from
it whenever a PRAM problem is suspected. Source
code is available from Wuttke at firstname.lastname@example.org.
A special quirk of PRAM in the Macintosh 630
models requires an additional step when zapping
the PRAM. In these Macs, one is supposed to push
"a red button near the SCSI connector on
the logic board" whenever the logic board
is removed and replaced.
When swapping NuBus cards in any Mac, it may
be important to clear some data out of a special
NuBus settings PRAM. Remove NuBus cards and power
up the computer once before installing the new
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