Quiz answer is: Characteristic impedance for routing DDR3 memories should be 50 ohm for single ended traces and 100 ohm for differential traces.
Where these values come from? It’s will be subject to a bit longer post which I will do this week🙂
I’ll try to answer these questions: What is characteristic impedance? Were these numbers 50 / 100 ohms come from? How we decide how to stack-up PCB layers before start design with DDR memory?