Quote Originally Posted by Rickpatbrown View Post

How fast does an electrical signal travel along a trace?
It depends on PCB material.
Normally it is (light speed*speed coefficient of material). On normal PCBs the speed coefficient is about 0.85.

The signals travel at 85% of light speed on a normal PCB, roughly.

It is about 25 cm every ns, 0.25 mm/ps.

The difficult is that the lines are powered by an RF signal at about 500 MHz and the electrical lenght of the path (so the difference in lenght between channel A and channel B) is depending on the frequency and the impedance of the lines.

So the adjustement of skew has to be done in different way at any RAM frequency.