Bump mapping vs Displacement (plus displacement nodes in Cycles)? Learning Blender+Cycles (2.79b), I'm trying to experiment with vertex displacement and bump mapping.

My understanding: bump mapping is to adjust face normals and create shadows/highlights suggesting (inexistent) height variations, while displacement truly changes the vertex height.

In Cycles:


I created bump mapping using a bump map for the normal value of a Diffuse BSDF node.
I tried to create actual displacement using the displacement input of the Material Output node.


On the left, the bump mapping result, on the right the displacement result:

  

It appears the result is the same (for the magenta texture), and looking at the edge of each sphere confirms no displacement of mesh vertices.

Material settings used

For bump mapping:

  

For displacement:

  

Question 1: How does work the Displacement input of the Material Output node? The latest documentation (2.79) talks about three modes (bump mapping, displacement, both), but doesn't explain how to use modes.

Question 2: In the documentation (2.79) two nodes are expected to be connected to the Material Output node: Displacement and Vector Displacement. Both seems to be about actual displacement. None are present in the latest version of Blender (2.79b). Have they been replaced or removed in 2.79b?

I saw in the jumble of Blender forums, that Displacement may be only accessible when the Feature Set option is set to Experimental in Render tab of the Property Editor. But activating the option does do nothing (even with Blender restarted).
Question 1: How does the Displacement input of the Material Output node work?


Depends what feature set you are using for rendering:


In Supported feature set it does Bump mapping, same as plugging Bump node into all your shaders.
In Experimental feature set is follows what you set in the Material properties:



So for True Displacement you need to set the feature set to Experimental, and set a setting for the Material. More on this here:

Blender Cycles True Displacement



  Question 2: In the documentation (2.79) two nodes are expected to be connected to the Material Output node: Displacement and Vector Displacement.


The documentation is continuous work in progress and does not adhere to any specific Blender version. There might be sections outdated or put beforehand of features that will come in future, like in this case Vector displacement.