The control language (CL), menu options, and system messages
control the operation of the system.
Control language
Control language (CL) is the primary interface to
the operating system. CL can be used at the same time by users at different
workstations, in batch and interactive jobs and in CL programs and procedures.
Menus
The system provides a large number of menus that allow
users to perform many system functions just by selecting menu options.
Messages
A message is a communication sent from one user, program,
or procedure to another.