I installed this lot 2x4 GB on my Imac recently purchased (version 10.7 Therefore mid 2011) and I have had no problems. Also this command reached me in by 72h00 recommended against signature in a very correct packaging given the fragility of this article that I recommend to all. I performed the update Moutain (Version 10.8) on my iMac and no not at this level disruption: all is well.