I bought these memory modules to give a facelift to my 2009 iMac (4GB) who rowed still OK after switching to 10.09 and it continued with 10.10 Yosemite. I installed the bars and everything seemed ok: they were well detected and taken into account by the system. However, I quickly found my iMac reboots, following Kernell panics and I told myself that it was beginning to let go of me and I began to watch the Apple refurb ... So, I wanted to put these barrettes in my unibody MacBook and I've realized that it was then afflicted by the same concern of accidental activation! Verdict: One of the two bars was faulty and it was she who made me panic! Now my iMac is 6GB and more concern ... Unfortunately, I've realized the problem after 30 days authorize the return. Too bad for me for my lack of foresight ...