Unterschied zwischen IKJEFT01 und IKJEFT1B

Hier ein Auszug aus dem TSO Users Guide

3.4.4.1.2 EXEC Statement

The program needed to execute TSO/E commands from the background is a terminal monitor program (TMP), which may be one of the following: IKJEFT01, IKJEFT1A, or IKJEFT1B. The EXEC (execute) statement is used to execute program IKJEFT01 or the alternate programs IKJEFT1A and IKJEFT1B. The format is:
//stepname EXEC PGM=IKJEFT01,DYNAMNBR=nn,PARM=’command‘
Note: The TSO/E terminal monitor program must not run as a V=R program. Executing the TMP as V=R will cause unpredictable results.
stepname is optional and can be used as a step identifier in programs consisting of more than one step.
EXEC is the JCL term that identifies this type of statement.
PGM= specifies the module being executed. In addition to IKJEFT01, there are two other entry points available for background execution that provide additional return code and abend support. The differences among the three entry points are:

**PGM=IKJEFT01
When a command completes with a non-zero return code, the program goes to the next command. When a command abends, the step ends with a condition code of 12 (X’C‘).

**PGM=IKJEFT1A
If a command or program being processed by IKJEFT1A ends with a system abend, IKJEFT1A causes the job step to terminate with a X’04C‘ system completion code. IKJEFT1A also returns to the caller the completion code from the command or program in register 15.
If a command or program being processed by IKJEFT1A ends with a user abend, IKJEFT1A saves the completion code in register 15 and then terminates.
If a command, program or REXX exec being processed by IKJEFT1A returns a non-zero return code to IKJEFT1A, IKJEFT1A saves this return code in register 15 and then terminates. Non-zero return codes to IKJEFT1A from CLISTs will not affect the contents of register 15 and the TMP will continue processing.
For a non-zero return code or an abend from a command or program that was not given control directly by IKJEFT1A, no return code is saved in register 15, and IKJEFT1A does not terminate.

**PGM=IKJEFT1B
If a command or program being processed by IKJEFT1B ends with a system or user abend, IKJEFT1B causes the job step to terminate with a X’04C‘ system completion code. IKJEFT1B also returns to the caller the completion code from the command or program in register 15.
If a command, program, CLIST, or REXX exec being processed by IKJEFT1B returns a non-zero return code to IKJEFT1B, IKJEFT1B saves this return code in register 15 and then terminates.
For a non-zero return code or abend completion code from a program or command that was not given control by IKJEFT1B, no return code is saved in register 15, and IKJEFT1B does not terminate.

See z/OS TSO/E Customization for information on abend and non-zero return code processing by these alternate programs, as well as conditional disposition processing for data sets.
DYNAMNBR= indicates the number of system resources the system should hold in anticipation of reuse. For information on the specific number of allocations you can specify, see z/OS MVS JCL Reference.
PARM= is optional and can be used to supply the first (or only) command to be executed. This is used most often when you only execute one command in the step.