From Load to a running system
The load address names the disk to start from; the load parameter names the device holding the I/O configuration, the LOADxx member to use, how chatty and interactive start-up should be, and the nucleus. From there, nucleus initialisation reads parmlib, the master scheduler starts, and JES2 and the subsystems follow.
The two values you type
| Field | What it is | Example |
|---|---|---|
| Load address | The device number of the system residence (sysres) volume that holds the start-up program | 0A80 |
| Load parameter, positions 1-4 | The device that holds the IODF (I/O definition file) and SYS0.IPLPARM | 0A82 |
| Load parameter, positions 5-6 | The suffix of the LOADxx member to use | 01 (LOAD01) |
| Load parameter, position 7 | The IMSI character: which messages to show and which prompts to issue | T |
| Load parameter, position 8 | The nucleus suffix | 1 (IEANUC01) |
The IMSI character
The initialisation message suppression indicator (IMSI) decides whether informational messages appear during start-up, and whether the operator is prompted for the master catalog and for system parameters. A period or blank shows few messages and prompts for nothing: everything comes from parmlib.
| IMSI | Informational messages | Master catalog prompt | System parameters prompt |
|---|---|---|---|
| . or blank | No | No | No |
| M | Yes | No | No |
| T | Yes | No | Yes |
| A | Yes | Yes | Yes |
| S | No | No | Yes |
LOADxx: where everything else is found
The LOADxx member, in SYS0.IPLPARM or SYS1.PARMLIB, points to the rest of the configuration. Its statements include IODF (the I/O definition), NUCLEUS, SYSCAT (the master catalog), PARMLIB (the parmlib concatenation), IEASYM (system symbols) and SYSPARM (which IEASYSxx members to use).
Nucleus initialisation and parmlib
Nucleus initialisation (NIP) builds the basic system: storage, the I/O configuration, the master catalog and the link pack area. It reads the IEASYSxx members of parmlib, which name further members: for example PROGxx for APF-authorised libraries and the link list, and COMMNDxx for commands to issue at start-up. If the IMSI asks for it, NIP prompts the operator with IEA101A, where extra parameters can be given, such as CLPA or SYSP=01.
IEA371I SYS0.IPLPARM ON DEVICE 0A82 SELECTED FOR IPL PARAMETERS IEA246I LOAD ID 01 SELECTED IEA246I NUCLST ID 00 SELECTED IEE252I MEMBER IEASYS00 FOUND IN SYS1.PARMLIB *00 IEA101A SPECIFY SYSTEM PARAMETERS FOR z/OS 03.01.00 HBB77E0 R 00,CLPA,SYSP=01
CLPA, or a quick start
The pageable link pack area (PLPA) holds widely shared, read-only modules. CLPA tells NIP to create it again from the LPA libraries, which is needed when maintenance has changed modules there. Without CLPA, the IPL is a quick start that reuses the PLPA from the page data sets, which is faster but keeps the old modules.
The master scheduler, JES2 and the rest
- The master scheduler starts and processes start-up commands, for example from COMMNDxx.
- JES2 starts and, unless its start options already say how, asks how to start ($HASP426). A warm start keeps every job and all output on the spool; a cold start reformats the job queues and loses them. Cold starts are rare and decided by the systems programmer.
- Automation then starts the network (VTAM, TCP/IP), security, Db2, MQ, CICS and the rest in the right order, and the system is ready for work.
In load parameter 0A8201T1, which LOADxx member is used? (for example LOAD05)
Show a hint
Positions 5 and 6.
Show the solution
LOAD01.
Examples are for learning. Run commands and jobs only on a system you are authorised to use, such as a training or test system, and never on production without approval.
Common mistakes
It is four separate fields: IODF device, LOADxx suffix, IMSI character and nucleus suffix. Check each one against the run book.
A quick start reuses the old link pack area, so the new modules are silently not loaded.
WARM keeps the work queues; COLD loses them. Always use the run book.
What you will see at work
- Systems programmers keep the LOADxx, IEASYSxx and other parmlib members under change control, because a typing mistake can stop the next IPL.
- Many sites keep two system residence volumes, so maintenance can be prepared on one while the system runs from the other.
- Automation products start and stop subsystems in a defined order, so operators rarely start CICS or Db2 by hand after an IPL.
Key terms
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