Difference between $S_{xx}$ and $s_{xx}$

Question

What is the difference between $S_{xx}$ and $s_{xx}$? I understand that $S_{xx}$ = $\Sigma_{i=1}^n(x_i - \bar{x})^2$ but how does this formula compare to the formula for $s_{xx}$?

Answer 1

$$ SS_{xx} =\Sigma_{i=1}^n(x_i - \bar{x})^2$$ and $$s_{xx} =\Sigma_{i=1}^n x_i^2$$

Answer 2

$S_{xx}$ and $s_{xx}$ both are standard deviation but $s_{xx}$ is unbiased estimator of $\sigma$. $$S_{xx}=\frac{\Sigma_{i=1}^n(x_i - \bar{x})^2}{n}$$ and $$s_{xx}=\frac{\Sigma_{i=1}^n(x_i - \bar{x})^2}{n-1}$$