already have 2x2GB 1333 DDR3 want to add 2x4GB 1333 DDR3

Solution
Well matched does not mean very much if they have never been tested together. Memory is sold in kits and is not guaranteed to work if you want to mix up some.

Of course, nothing is stopping you from doing that. You will take responsibility for doing your own compatibility testing.
Well matched does not mean very much if they have never been tested together. Memory is sold in kits and is not guaranteed to work if you want to mix up some.

Of course, nothing is stopping you from doing that. You will take responsibility for doing your own compatibility testing.
 
Solution