The sorter is constructed out of several different kinds of modules. These modules have a specific task in checking in and sorting the material. A minimum configuration of modules is one front end-module and one sorting module or a single Compact sorter module. There is no maximum number of modules; the only real limit is the space available.

The most interesting module is the front end (also referred to as inlet). A front end handles the checking in of the material and controlling the rest of the sorter for where to sort a specific item. A front end contains a computer with LibRetto 2 software.