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I have a MacBook Pro.

I have an external monitor that I'm using. When I mirror my display there are black edges.

When I don't mirror my display, and use it as an extended monitor the entire screen is filled up with no black edges.

How can I fill the entire screen when mirroring my display?

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up vote 1 down vote accepted

Are these displays the same resolution? Unless they match, this is going to happen. You might be able to force one into a lower resolution but if it's a different aspect ratio it'll either stretch or letterbox like this (this depends on the monitor, some might have a setting for it). If you can be specific about the model of Macbook and monitor, and the resolutions you're trying to use, then we can be sure but I'm willing to bet this is what's going on.

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yes they have different resolutions. and your answer makes sense. it will default to the lower res... – Sheehan Alam Nov 24 '10 at 21:50
@Sheehan If the external display is an LCD, the output quality will be reduced significantly if you stretch it. It's fine for video, but not everyday web browsing and reading. If you want to mirror, you'll have to live with that. – Daniel Beck Nov 25 '10 at 11:18

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