Complex sentence: W-buffering provides a linear representation of distance in the depth buffer, whereas z-buffering is nonlinear and allocates more bits for surfaces that are close to the eyepoint and less bits for those farther away.
Split into simpler sentences: W-buffering provides a linear representation of distance in the depth buffer. Z-buffering is nonlinear and allocates more bits for surface that are close to the eyepoint and less bits farther away.