> early wolfenstein and doom days.

Wolfenstein yes, Doom no. Wolfenstein 3D used a very simple raycasting method that just shot rays out from the player's position to render a 2D level in psuedo-3D. Doom, while still technically using raycasting, uses a much more complicated method that involves BSP trees.

A quick google search found this page, which explains it much better than I can: http://doom.wikia.com/wiki/Doom_rendering_engine