An MVS™ subsystem consists of two control blocks and a set of functional routines, all resident in common memory. The control blocks are:
The subsystem is active when the SSCT contains a nonzero pointer to the SSVT, and inactive when the pointer is zero.
Each subsystem is defined to MVS by an entry in an IEFSSNxx member of SYS1.PARMLIB. (See the OS/390 MVS Initialization and Tuning Guide, SC28-1751.) Each subsystem can be defined with an initialization routine and some initialization parameters. The CICS® subsystem is defined with an initialization routine of DFHSSIN, and an initialization parameter that specifies the name of an additional member of SYS1.PARMLIB, which contains further CICS-specific subsystem parameters. These parameters specify whether the console message handling facility is required.
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