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The Parameter RAM (PRAM)
in the Mac is a small amount of RAM that stores the settings
of several control panels and some system software settings.
The PRAM is powered by a small battery, often 1/2 AA 3.6V,
located on the main logic board. PRAM is similar in function
to CMOS settings on a PC.
The most common
signal that the PRAM needs to be cleared out is when the clock or
monitor settings change from one startup to the next. Some
other signals include: inability to boot off a connected SCSI
device, if a serial port can't be accessed because it claims
that it is in use, if documents won't print, if the monitor
will not come on at startup, or if you get persistent and
frequent errors, especially Type 11 errors, that don't seem
to be linked to any recent event. The above described events
are not solely caused by corrupted PRAM, but they are most
commonly related to PRAM problems.
When starting up a Mac,
or after a restart, immediately hold down the
Command-Option-P-R keys. On startup you will
hear the first system chime (which is normal and will happen
whether you are holding down the keys or not). Continue to
hold the keys down until you hear two subsequent chimes.
After a three total system chimes you can let go of the keys
and let the Mac continue to startup normally.
After clearing out the PRAM, it may be necessary to redo
the settings in some affected control panels after clearing out
the PRAM. If the problem persists after clearing out the PRAM the
battery may need to be replaced.
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