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There is no equivalent function in OS/390. Many users write their own routine to
replace the PAUSE function, if needed, or use the existing automation functions
of OS/390.
4.3.4 Allocation of Resources
The allocation of resources in OS/390 occurs at step initialization time. This is a
big difference from VSE where allocation of resources occurs at open time. In
OS/390, if the JCL contains DD statements that point to data sets, the data sets
are allocated even if they are not opened. This makes IEFBR14 useful in testing
out allocations or in allocating new data sets.
In MVS, IEFBR14 can be used to run a job with no program execution. This
causes all JCL to go through conversion and interpretation. Using IEFBR14 in
VSE would not cause a file to be opened, so no allocation of resources could
take place.
With MVS, the system allocates the resources when a job step is started. The
volumes have to be mounted, the devices have to be available, the system data
sets have to be there and the region has to be available. If there are data sets in
your JCL, they have to be cataloged and the volume information must be
specified. If more tape drives are required than are available to execute the job,
the job will wait until sufficient tape drives are made available.
With MVS, the scope of allocation is generally the current step. JCL statements,
such as the DD statement, affect only the current job step. This is very different
from VSE where the ASSGN statement can secure a tape drive for the duration
of the job. In OS/390, a tape drive deallocated at the end of a step may be
″stolen″ by another JOB before the beginning of the next step, causing the tape
to be dismounted and a mount message to be issued on another tape drive.
4.3.4.1 Resource Allocation at Open Time
With VSE JCL, allocation of resources is done at OPEN time. The JCL can
contain numerous DLBL or TLBL statements, even for files that do not exist; as
long as the application does not open them, they′re just ignored. This is
completely different in OS/390 where files specified in JCL are allocated at step
initiation time, whether the application opens them or not. See item 4 on
page 71.
4.3.5 Hidden JCL
Hidden JCL doesn′t appear in the job stream but is used during the execution of
the job. It can be the permanent assignments, labels in the partition or system
standard label areas, or ″carryover″ (described below).
4.3.5.1 Partition and System Standard Labels
File definitions stored in the partition and standard label areas do not appear in
the VSE JCL. In OS/390 all file definitions are coded in the JCL.
System standard labels provide a set of labels that is common to the whole VSE
system.
Partition standard labels provide a set of partition specific file definitions. These
file definitions are different from one partition to another. This function can be
used for application, sort or compiler work files. This may have an impact on
78 VSE to OS/390 Migration Workbook