> calculates display on the Moi screen are made from "polygons"
> based from nurbs or directly from "nurbs" ?

The display is made by polygons that are calculated from the NURBS surfaces.

But the shading information at the corners of the polygons (called "vertex normals") does come directly from the NURBS surface though - that helps the polygons get shaded to look more similar to the true surface.

3D video cards basically are built around processing polygons, there is generally no way to send the NURBS surface data directly to the video card, they are just not really constructed with that ability.

- Michael