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Originally published July 15, 2011 at 4:56 PM | Page modified July 15, 2011 at 7:33 PM

App extends desktop wirelessly

Since my eyes were opened to the wonders of working with multiple monitors many years ago, I've used the following setup while working:...

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Since my eyes were opened to the wonders of working with multiple monitors many years ago, I've used the following setup while working:

My MacBook Pro is connected to a 20-inch external monitor, with the Displays preference pane set to span my desktop over the breadth of the display and the laptop's built-in screen. The external is my main screen, where I do most of my work, and the MacBook Pro is where I keep iChat, Twitter, Skype, and other applications that can be consulted at a glance.

But it's not enough. I can always use more screen real estate.

The problem is the MacBook Pro offers only one video-out port, so I can't just add another external display. (This is last year's model. The current Thunderbolt-equipped MacBook Pro can chain displays in theory, although no monitors are available that take advantage of the capability.)

However, I do have a second 20-inch display set up next to my primary display — but it belongs to the Mac mini I use as a test machine and home-entertainment server. That display is usually powered off.

That is, until I installed Avatron's Air Display software ($19.99, on both machines. Air Display sends video data over your Wi-Fi or Ethernet network instead of through a dedicated hardware port.

Setting up Air Display is a little convoluted, requiring that you install the app from the Mac App Store, and then download a separate file that installs the Air Display preference pane and core components. Avatron has done a good job of explaining the steps, however.

With the software running on both computers, I selected the name of the Mac mini from an Air Display menu bar icon (or you can do it in the preference pane). Both screens turned blue as the MacBook Pro adjusted to the newly connected monitor, and then my desktop background appeared in a window on the Mac mini's screen.

As far as the MacBook Pro knows, it's just connected to another hardware display. Arranging the placement of the displays in software — to specify that the second external monitor was located to the left of the first, in my case, and that I wanted the desktop to be spanned, not mirrored — was done through the Mac OS X Displays preference pane.

Given that the data need to zip over a network instead of a dedicated video cable, the video performance and screen refresh can sometimes be a little jumpy. But only a little. I can watch HD movie trailers on the Air Display screen with few signs of dropped frames or image compression. I wouldn't want to use it as a secondary display for editing video, but for expanding my desktop and giving me more room to make documents visible, it's perfectly fine.

As an aside, Air Display also convinced me of a key benefit of Apple's Mac App Store. After getting accustomed to working with a third display at home, I was disappointed to go into the office where I have just one external monitor. However, I also had the 27-inch iMac that Apple loaned me for review, occupying the left side of my desk.

I was able to open the Mac App Store on the iMac, sign in using my Apple ID, view my list of purchases, and install Air Display directly. After a restart, the iMac was acting as a quite spacious third screen.

Air Display isn't limited to running on another Mac. Software is also available to press a Windows PC into service, and you can purchase Air Display for iOS ($9.99, to use an iPhone or iPad as an additional display.

It seems extremely odd at first, but with an iPad in a stand and Air Display running, there's plenty of screen real estate to hold one or two applications' windows on the iPad. Who said an external display needed to be a monitor, after all?

Jeff Carlson and Glenn Fleishman write the Practical Mac column for Personal Technology and about technology in general for The Seattle Times and other publications.

Send questions to More Practical Mac columns at


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