I have a Macintosh [MacBook Pro] with multiple monitors. There's the built in laptop display and I additional have a Apple Thunderbolt Display and another third party monitor attached via Thunderbolt/DisplayPort adapter. This is a total of three displays.

When, in an application, I open a new window, the new window doesn't often open on the display I which currently had focus, but seems to open randomly across the three displays. That is I may have an open, active, foreground window on the Thunderbolt Display and when cmd-N'ing to open a new window it may open on the laptop screen or the third display.

How is Mac OS X deciding which display to open the new window on and can this be selectively changed to alway open on the currently active display?

  • What version of OS X?
    – NSGod
    Nov 7, 2014 at 18:05

2 Answers 2


If you right click on any icon in your dock, you could assign an app to a display.

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Using an answer to be able to post image...

Monitor differentiation looks like it's new to Yosemite. Mavericks doesn't show anything beyond simply assigning a Desktop, unfortunately.
There is the possibility it's affected by having monitors set to separate spaces or not, but I'm not going to break 12 Spaces of setup just to test that theory ;-)

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I do find some apps will remember which screen, some will not, consistently. MS Remote Desktop will certainly not, for me. Though it will remember which screen the initial remote list window should be on, every remote session I open launches on the Primary monitor.

I think in the OP's case, an added complexity may be that, as it's a laptop, the external screens may not always be connected. Once a screen is removed, the Finder will force any window on that screen back to the Primary. I don't know whether that would be 'remembered' even if the app wasn't launched at any time its preferred monitor was disconnected.

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