Well my decision was not to buy on Amazon. Nothing against Amazon, which has always geklalppt fine. But finally, no experience, what memory had to be on my iMac right.
But when I sties in this memory and the mostly good evaluation read, I pulled myself together. I ordered and could not wait to post the small package delivered.
That was the first hurdle.
I have put my iMac on a thick rug, unscrewed storing compartment and found that the memory mechanically fit.
That was the second hurdle.
I closed the storage compartment, closed to all cable and await with interest the image which I showed to me now. My Mac started. Shortly after I had taken 4 GB RAM now the expected 12 GB.
This was the third and final hurdle.
It's worked out. I'm happy my iMac RAM us is again swift as an arrow.
Oh and Aperture works perfectly and quickly.