Here is some scans from my Bucyrus-Erie 22-B manual showing the cable routing and top-down view of the boom for the shovel.
The Bucyrus-Erie 22-B is a cable type machine, if you look at the cable routing two cables wrap around a pulley in the boom, one cable goes to the top of the dipper and the other to the bottom, when the drum at the pivot of the boom is rotated one cable unwinds and the other is wound pulling the dipper in or out.
-Shawn-