DSP Builder 15.1 : Parallel Floating-Point FFT

the DSP Builder Advanced Blockset's Handbook mentioned an example of FFT known as "parallel floating-point fft" and has as a model file " demo_parallel_fpfft.mdl"

and a second one named variable-size floating-point fft, its model file is demo_fpvfft.mdl.

Could anyone give me an explanation of what these designs examples demonstrate ?