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The 500GB model has two platters with 250GB a piece. Assuming the 320GB unit has two platters at 160GB a piece, the 500GB model will have higher areal density and that should be capable of sustaining higher read and write speeds than the 320GB model.

I have the 500GB model, myself.
 
I see...I ask because I thought 500GB is too much for causal use like video and photo editing...reading websites I will not use editing too much on my MBP I will use powerful desktop windows PC. I think 250GB is good enough instead of 320GB...No?
 
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