In dimension 4, PL and Diff agree, but Top differs. In dimensions above 6 they all differ. In dimensions 5 and 6 every PL manifold admits an infinitely differentiable structure that is so-called Whitehead compatible.
In dimension 4, PL and Diff are in agreement, whereas Top has a differing opinion. In dimensions greater than 6, they all hold distinct views. In dimensions 5 and 6, any PL manifold can have an infinitely differentiable structure that is known as Whitehead compatible.