The system shared code is loaded into the system address space (class 3/4 memory or privileged class 5 memory), and all tasks or users can access it. DBL ensures that this shared code is always write-protected, regardless of the value of the READ-ONLY attribute.
This memory area is controlled by the subsystem management (DSSM), since the shared code was loaded as nonprivileged subsystems (see the “Subsystem Management” manual [10]). For each subsystem, a list of visible symbols (which are to be known outside the subsystem) must be defined in the DSSM. Only these symbols, which are called “connectable entries”, may be specified in a START/LOAD-EXECUTABLE-PROGRAM or START/LOAD-PROGRAM command or in the BIND macro and are available for the resolution of external references.