IBM OS/390 User Manual

Page of 673
The VSE 
file-id (the label), which can be up to 17 characters long, is equivalent to
the MVS DSname, which can be up to 44 characters long.
4.3.10.4 MTC Statement
Magnetic Tape Control statements provide control over tape processing
including writing tape marks and unloading tapes. MTC has no direct equivalent
in MVS: OPEN automatically positions the tapes based on the LABEL parameter
of the DD statement and CLOSE rewinds or unloads volumes, depending on the
DISP parameter. Writing a tape-mark (MTC WTM) can be achieved with
IEBGENER, as follows:
//WTM
EXEC PGM=IEBGENER
//SYSPRINT DD SYSOUT=*
//SYSIN
DD DUMMY
//SYSUT1
DD DUMMY,RECFM=F,BLKSIZE=80
//SYSUT2
DD UNIT=TAPE,LABEL=(,NL)
4.3.10.5 ASSGN Statement
In VSE, the relationship between a logical unit (SYSxxx) used by a program, and
a physical device used to contain a file is established by the ASSGN JCL
statement. These assignments can be made temporarily -- that is, they will
revert to a standard value at the end of a VSE JOB or when a RESET statement
is processed, or they can be made permanent, where they will become the new
persistent value.
Often ASSGN standards are established during system initialization and JCL will
not explicitly repeat those ASSGN statements. Further, in the case of VSAM files,
ASSGN processing is handled automatically by VSAM without the need for any
ASSGN statements.
In MVS JCL, the closest analog is the use of the UNIT= parameter on a DD
statement.
4.3.10.6 RESET Statement
The RESET statement resets the current temporary ASSGN value and the
assignment of the logical unit will revert to its current permanent value.
There is no equivalent of this function in MVS JCL in OS/390, as there is no
persistence or 
carry-over
″ 
of device allocations from one job step to another.
4.3.10.7 DLBL and EXTENT
The DLBL and EXTENT statements provide information for disk files. The DLBL
provides information such as the filename (7-character name), the file-id (1-44
character name), retention period, file type (VSAM, SD, DA) plus more. The
EXTENT provides volume information and extent information for new data sets.
VSAM files don
t require EXTENT statements. The VSE 
filename is equivalent to
the MVS DDname and the VSE
 file-id is equivalent to the MVS DSname. The
filename (DSname) is the name written to the VTOC.
4.3.10.8 CAT=Catalog on DLBL
Another of the VSE differences is that the catalog is specified on the DLBL
statement. It is similar to having a //STEPCAT for every DD statement for VSAM.
Each disk file can have its own catalog pointer. This provides the ability to have
VSAM files that have the same name in different catalogs. When these files
having the same name are migrated, consideration must be given to the target
Chapter 4. Job Control Language (JCL) Differences and Considerations
83