That's the thing cuz the 320 is a few months newer and it's quad core and has more ram 6gb to 4gb like genoc1de said but it also has a smaller Hard drive 500gb to 750fb of the 310 and the 310 has 2.9ghz as where the 320 has 2.1gbz..?
I dunno to much about computers but why would a newer model...