Using Mirror Displays

I have a mid-2010 Macbook Pro with the Nvidia 330m. Does using Mirror Displays require any less system resources (such as VRAM) than Dual Displays? I mean it shouldn't right (assuming that you use the same resolution for Mirror and Dual) because there is still content on both screens being written to the VRAM?

 

Oh really? So using dual displays should be slower than mirror displays? Because I've noticed that using dual displays will have an initial choppiness with using expose/scrolling/etc. and then after a few times of doing Expose or whatever, it'll be get smooth. Of course, as soon as I do something else, and call on Expose again, it'll be jerky at first again.

Mirrored displays doesn't experience this, it's always smooth just like if I was using the laptop monitor and no external. So I thought something was up.