Callable shared object files are in an operating system format. They can be shared between processes; if two different system executables call, at the same time, a subprogram created as a callable shared object, that program is loaded only once and executed when called. The operating system shares the procedural code and creates separate data areas for each process.
A callable shared object is dynamically loaded and executed by the run-time system. Callable shared objects are not interpreted; their execution time is generally quicker than either intermediate or generated code.
Callable shared object files have the filename extension .so; for example, myprog.so.
Callable shared object files are created using the cob -z command; see the chapters COBOL System Interface (Cob) and Callable Shared Objects for details.