This article describes extended desktop where the Finder desktop area extends across multiple displays, as well as video mirroring, where the same image is visible on two displays.

Extended Desktop

Starting with the Macintosh II, when you have multiple video cards installed, the desktop area can be extended across as many displays as are connected to the computer. This holds true up through current Power Macintosh models which support the addition of video cards. All-in-One computers such as the Power Macintosh 5200 did not support extended desktop mode unless a video out card was installed. Apple did not market such a card for these computers.

Some PowerBook models supported the use of an external display, as evidenced by the presence of a video out connector on the back panel, yet may not support extended desktop. The original PowerBook G3, for example, allowed the use of an external display but would not drive both an external display and the internal LCD. Check your owners manual to determine if your computer supports extended desktop.

To configure extended desktop, enter the Monitors & Sound control panel. When you click the Arrange button you will see a representation of the displays currently connected to your computer, similar to that shown in the graphic below. This control panel allows you to determine which display will have the menu bar, which will be the startup display, and also allow you to arrange the logical desktop space to match the physical layout of your displays.

Figure 1 Monitors & Sound control panel

Video Mirroring

Video mirroring is a method for displaying the same information on two screens. This is particularly useful in a classroom or presentation setting where you need to be in front of an audience and use your computer also.

To verify if your computer supports video mirroring, check the Monitors & Sound control panel or Mac OS Help under the Help menu. Earlier versions of the Mac OS describe video mirroring as Duplicate Monitors.