Memories installed without any concern in the 2 slots free (although the "clipped" - it has to click).
I left the 2 x 2 Gb of origin and the system displays 12 Gb.
These additional 8 Gb significantly improve iMovie and iPhoto (although the effect will do more than feel iMovie iPhoto). For games, I tested Civilization V I set maximum video quality => great, the game is not only playable, but is significantly faster => brilliant. Starting the Mac also "boosted".
For a difference of 343 EUR compared to the official website of the brand, no hesitation.
