Iray is an interactive path-tracing for photo realistic rendering.
To use Iray on Mac OS X, make sure you install the latest NVidia drivers if your card is NVidia:
You can switch to Iray by going to the renderer menu in the 3D view.
Setting up IRay for material previews with displacement
When you want to create a nice preview of your material for portfolio purpose or to upload on Substance Share, IRay provides a quick way to add displacement to your preview mesh.
With IRay activated, go to Scene>Edit.
This will display all the objects in your scene. You can activate Subdivision on a per object basis if you object is not subdivided enough.
Choose Length, the default value of 0.1 should give you plenty of precision.
If you still don't see displacement on your mesh, it's because the Height Scale is set to 0 in your materiel settings.
Go to the Materials settings in the 3D View and choose Edit to see the properties and increase the Height Scale.
Here is the result!