As far as I know...all 27" iMacs with the "i" series processor have 4 ram slots (in fact all 27" iMacs have 4 ram slots). So you should be able to keep the 2 x 2gig sticks of ram that are currently in it...and then fill the remaining two empty slots with 2 x 4gig sticks of ram...for a total of 12 gig of ram.
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