Secondary input to the binder consists of files that are not part of primary input but are included as input due to the INCLUDE control statement.
The binder obtains its secondary input by reading the members from libraries of object modules (which may contain control statements), load modules, or program objects.
The binder accepts a load module that was generated by the Linkage-Editor input, and converts it into program object format on output.
The binder accepts previously bound program objects as input. This means that you can recompile only a changed compile unit, and rebind it into a program without needing other unchanged compile units. See Rebind a changed compile unit and Rebindability.
You can compile and bind each compile unit to a program object, possibly with unresolved references. To build the full application, you can then bind all the separate program objects into a single executable program object.