# RMSE vs Standard deviation in population

RMSE (Root mean square error) and SD (Standard deviation) have similar formulas.

The only difference is that you divide by $n$ and not $n−1$ since
you are not subtracting the sample mean here. The RMSE would then
correspond to $\sigma$ . Therefore, the population RMSE is $\sigma$
and you want a CI for that.

So I want to know whether RMSE and SD are the same. Also, I want reference about it.