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OS X: How to use multiple displays with your Mac in Mountain Lion and earlier

Learn how to use multiple displays with your Mac, with video mirroring or extended desktop.

When connecting external displays to your Mac, you have three options for configuring the displays: Video mirroring, extended desktop, and closed lid.

Video mirroring

Mirroring displays the same image on each display.

  1. Make sure your additional display is properly connected and powered on.
  2. From the Apple () menu, choose System Preferences.
  3. From the View menu, choose Displays.
  4. Click the Arrangement tab.
  5. Enable (check) "Mirror Displays" in the bottom-left corner.

In the example below. the blue boxes represent each display that is connected. The white bar at the top of both boxes represents your menu bar and is shown on both displays when they are showing the same information.

mirroring

When mirroring, your Mac attempts to match the closest resolution between the primary (or built-in) and secondary displays.

mirroring resolution samples

The usable resolution is the closest matching resolution for both the primary and secondary display. If you choose a resolution that is not supported on both displays, OS X reverts to using the closest matching resolution.

Extended desktop

With extended desktop, your displays are treated as one, continuous desktop.

  1. Make sure each display is properly connected and powered on.
  2. From the Apple () menu, choose System Preferences.
  3. From the View menu, choose Displays.
  4. Click the Arrangement tab.
  5. Disable (uncheck) "Mirror Displays".

In the Displays pane of System Preferences, each blue box represents a display that is currently connected. The size of each box is relative to the current resolution of the display it represents. In the example pictured below, the larger box on the left represents an Apple 27" Thunderbolt Display, while the smaller box on the right is the built-in display of a 13" MacBook Air (Color LCD).

The white bar at the top of the left blue box represents the menu bar you see at the top of your display. Menu bar placement determines which display is treated as the primary display in OS X. To change your primary display, click and drag the white bar from one blue box to another.

You can also drag any of the blue boxes to change a display's represented location. Use this feature to make sure the connected displays match their real world location when navigating your desktop.

As shown below, each display retains its maximum resolution setting as they are operating as individual displays showing a continuous desktop.

Closed lid

For instructions on using your Mac notebook with a closed lid and external display attached at the same time, see Mac notebooks: How to use your computer in closed clamshell (display closed) mode with an external display.

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Last Modified: Sep 2, 2014
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  • Last Modified: Sep 2, 2014
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