will I be able to get FULLHD using DVI?
You will be able to get much more than 1920x1080 over DVI, up to 2560x1600 if your monitor supports it.
Is there any difference between 1920x1080 and 1600x900?
320 horizontal pixels and 180 vertical pixels. Other than that, they're both 16 : 9 resolutions, and with the price of 1920x1080 panels these days, there is no reason to bother with 1600x900.
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