I have a iMac that is connected to an external monitor to extend my screen. Into that same monitor I have a separate Windows box that I need to run sometimes. The Windows box goes in through VGA and the iMac through HDMI. The problem I'm running into is that when I want to use the monitor for Windows, there is no simple way to get my iMac back to just that monitor. If I leave it extended, some apps are open in the other 'monitor' and I can't access them without work arounds. If I turn on mirroring, the resolution on the iMac drops significantly, even if I tell it to keep the iMac screen size. I can't turn the other monitor off as that defeats the point. I have to unplug the HDMI to get it to perform correctly. Is there any way (command line, an app, preferences, etc) to toggle between using the display and not on my Mac?
In case you're open to some other options, I run Windows under Parallels on an iMac with second display, and it's extraordinarily slick. Highly recommended if you're not gaming or something else intensive on the windows box.– NReilinghDec 9, 2013 at 5:28
I have VMware fusion, but in a development enviornment sometimes I need an extra tower. My work also provided it with windows already installed so I kind of have to keep it that way for licensing purposes.– emilykDec 10, 2013 at 5:31
There is no way to "virtually" disconnect a display on a Mac, like you can on Windows. The Mac needs to disconnect physically. The easiest way to do this is by purchasing an inexpensive KVM Switch, to physically switch between the Mac & PC.
This similar question has an answer that refers to SwitchResX. The marketing information for that application says SwitchResX can let you disable an unused Display.
Use VLC player to play your movies. Go to Preferences → Video and choose black screen when in full screen.