March 30, 1979
196.2 IBM VM/370 eMS User's Guide

Pg. of GC20-1819-2 Rev March 30, 1979 by Supp. SD23-9024-1 for 5748-XX8 When you create a tape in CMS using AMSERV, CMS writes a tape mark
preceding each output file that it writes. When this same tape is read
using AMSERV under CMS, HDR1 and VOL1 labels are checked using the
LABELDEF command you provide. If you read this tape in a real DOS/VS system, you should use a TLBL card instead of the LABELtEF command. Similarly, when you create a tape under a DOS/VS system using access
method services, if the tape is created with standard labels, CMS AMSERV has no difficulty reading it.
The only time you should worry about positioning a tape created by AMSERV is when you want to read the tape using a method other than AMSERV, for example, the MOVEFILE command. Then, you must forward space
the tape past the label, using the CMS TAPE command before you can read
it.
Defining OS Input and Output Files !2te: This information is for OS/VS VSAM users only. VSE/VSAM users
should refer to "Defining DOS Input and output Files" for information on
defining files for use with VSAM. If you are going to use access method services to manipulate VSAM or SAM files or you are going to execute VSAM programs under eMS, you must use
the DLBL command to define the input and output files. The basic format
of the DLBL command is:
DLBL ddname filemode DSN datasetname (options
where ddname corresponds to the FILE parameter in the AMSERV file and
dataset name corresponds to the entry name of the VSAM file, that is, the
name specified in the NAME parameter of an access method services
control statement.
If you are using a CMS file for AMSERV input or output, use the CMS operand and enter CMS file identifiers as follows:
dlbl mine a cms out file1 (vsam
The maximum length allowed for ddnames under CMS VSAM is seven
characters. This means that if you have assigned eight-character ddnames
(or filenames) to files in your programs, only the first seven
characters of each ddname are used. So, if a program refers to the
ddname OUTPUTDD, you should issue the DLBL command for a ddname of OUTPUTD. Since you can encounter problems with a program that contains
ddnames with the same first seven characters, you should recompile those
programs using seven-character ddnames.
There are several options you can use when issuing the DLBL command
to define VSAM input and output files. These are: • VSAM, which you must use to indicate that the file is a VSAM file.
Note: You do not have to use the VSAM file if you are using any since they imply that the file
ddnames (filenames) IJSYSCT and
being defined is a iSAM file. VSAM option to identify a file as a
of the other options listed here,
is a VSAM file. In addition, the IJSYSUC also indicate that the file
Section 10. Using Access Method Services and VSAM 197