LPA
The link pack area: a part of storage shared by every address space, holding programs that many tasks use at once.
Also written link pack area, PLPA, LPALST, dynamic LPA, SETPROG LPA
The LPA, or link pack area, is an area of virtual storage that every address space can see. It holds programs that are used by many jobs and users at the same time, so only one copy needs to be in memory.
Programs in the LPA must be reentrant: written so that many users can run the same copy at once without changing it. Most of the LPA is loaded at IPL from a list of libraries called LPALST, set in PARMLIB. Programs can also be added while the system runs, using the SETPROG LPA command, which is called dynamic LPA.
When a job step runs a program, z/OS looks for it in a fixed order: first STEPLIB or JOBLIB, then the LPA, then the link list. So a program in the LPA is found before one in the link list.
That order matters during changes. If a new version of a program is put in a link list library but an old copy is in the LPA, the old copy keeps being used. System programmers handle LPA changes carefully, usually as part of planned maintenance.
Where can I learn this hands-on?
Right here, at ZedBank. You take a junior job at a simulated bank and learn each part of the work by doing it, with Zed beside you. There's nothing to install.
Start at ZedBankRelated
- STEPLIBA DD statement that tells z/OS which libraries to search first for the program a job step runs.
- Load moduleThe runnable form of a program, stored in a library, which JCL executes by name.
- Virtual storageThe memory each address space sees, which z/OS maps onto real memory and disk so that every program appears to have its own large space.
- PARMLIBThe library of members that holds z/OS's own settings, read when the system starts and on some commands.
- IPLInitial program load: starting z/OS on a system, the mainframe word for booting.