IBM OS/390 manual MTC Statement, Assgn Statement, Reset Statement, Dlbl and Extent

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 ²carry-over² 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-idis 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