The Mac OS X menu bar provides quick access to some of the system preferences you frequently change. Clicking a preference’s menu bar icon reveals all of the available options for that system preference.   By default, Mac OS X turns on certain menu bar items (such as Sound and AirPort). Others (such as Displays) must be turned on in System Preferences.

Getting Started with Mac OS X version 10.2 > Configuring and Customizing Your Mac > Accessing Menu Bar Preferences

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