I have no idea which one I should get for my prebuilt. I have 8gbs so far but I can afford to push it to only 12gb. Does it matter which type of RAM I get? the HP site only gives me a specification for DDR3 1333MHZ but nothing on the "E" or "U", what do these mean and which one should I get? Both of these cost the same price 4GB (2 x2GB).