Is gather* equivalent to displaymath?

Question

Is gather* with one line of math equivalent to displaymath?

Answer 1

No, it is not: the vertical spaces before and after the display are different.

\documentclass{article}
\usepackage{amsmath}
\begin{document}
\noindent Text
\begin{gather*}
  a=b
\end{gather*}
Text
\begin{displaymath}
  a=b
\end{displaymath}
Text
\end{document}