Depending on the configuration of the operating system and the macros used to pass control, execution of the load modules is serial or in parallel. Execution is serial in the operating system unless you use an ATTACH or ATTACHX macro to create a new task. The new task competes for processor time independently with all other tasks in the system. The load module named in the ATTACH or ATTACHX macro is executed in parallel with the load module containing the ATTACH or ATTACHX macro. The execution of the load modules is serial within each task.
The following paragraphs discuss passing control for serial execution of a load module. For information on creating and managing new tasks, see Creating the task.