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It will play it smoothly, and can easily output it to an external monitor, but of course the built-in screen is only 1440x900
 
Okay, but I think 4GB is totally enough for smooth HD playing, isn't it?
 
Yes, I know. But 8GB doesn't make the display 1080p, does it? ;) So I think HD video playing is as smooth with both 4GB and 8GB RAM.
 
Are you serious? My 1.6ghz Core2Duo with 2GB played back 1080p smoothly, that should give you a hint.
 
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