a post processor is a unique "driver" specific to a cnc machine, robot or mechanism; some machines start at different locations or require extra movement between each operation, the post-processor works with the cam software or off-line programming software to make sure the g-code output or program is correct for a specific trademark machine control cabinet (fanuc, siemens-sinumeric, mazak-mazatrol, heidenhein, deckel-maho, etc.