How to create a smooth looking object that also has sharp edges like this disc in Blender 2.8:
To do that, apply smoothing to both the geometry of the model and the appearance of the surface. In both cases prevent the smoothing to occur at the edges that must remain sharp as explained below.
Smooth the mesh
Use the Subdivision Surface modifier to smoothen the mesh. Set the value of the Crease property of the edges that need to be sharp by selecting those edges, press
Shift-E, then enter 1. The shortcut
Alt-LMB to select an edge loop comes in handy here.
Edge Crease is also available in the Edge menu in Edit mode.
Smooth the surface
Activate Smooth shading of the model to render each point using interpolated normals. As above, prevent the smoothing effect in undesirable places. This can be done by activating Auto Smooth, which is found under Object Data Properties/Normals.
Auto Smooth replaces the Edge Split modifier. It is advised not to use that modifier any longer.