Link pack area (LPA) and extended link pack area (ELPA)
The link pack area (LPA) contains all the common reentrant modules that are shared by the system.
- Economy of real storage by sharing one copy of the modules
- Protection: LPA code cannot be overwritten, even by key 0 programs
- Reduced path length, because modules can be branched to.
It has been established that a 2 MB LPA is sufficient for MVS when using CICS® with MRO or ISC, that is, the size of an unmodified LPA as shipped by IBM®. If it is larger, there are load modules in the LPA that might be of no benefit to CICS. There might be SORT, COBOL, ISPF, and other modules that are benefiting batch and TSO users. You must evaluate whether the benefits you obtain are worth the virtual storage that they use. If modules are removed, check whether you need to increase the size of the regions they run in to accommodate them.
The pageable link pack area (PLPA) contains supervisor call routines (SVCs), access methods, and other read-only system programs, along with read-only re-enterable user programs selected by an installation to be shared among users of the system. Optional functions or devices selected by an installation during system generation add additional modules to the PLPA.
The modified link pack area (MLPA) contains modules that are an extension to the PLPA. The MLPA can be changed at IPL without requiring the create link pack area (CLPA) option at IPL to change modules in the PLPA.