Pg. of GC20-1819-2 Rev March 30, 1979 by Supp. St23-9024-1 for 5748-XX8 • When the user has not specified a block count routine in his DCB EXIT list under OS/VS, the program abends when a block count error occurs. Under eMS, this condition produces a message that asks whether or net
to abend the operation. • Certain fields in HDRl and EOFl labels default to values different
from those under OS/VS. These values can always be specified in a
LABELDEF command if the user does not like the default values. For
example, the default for data set name in an output label under OS simulation is DDNAME and not DSNAME. The default data set sequence
number is always one even when the data set is not the first data set
on the tape. The default volume sequence numter is always one. Read
the section on the LABELDEF command in this manual to learn what the
default values are under eMS. You can find what default values are
in OS/VS by reading the IBM publication Note that
you can always get exactly what you want written on a tape label by
explicitly specifying the field on a LABELDEF command. For example,
you can specify DSNAME as FID on such a command and have it written
in the label instead of DDNAME. • Default volids (when you do not specify a volid in a
FILEDEF statement) in output HDRl and EOFl records under CMSOOl and will not be the actual volume serial in the
already en the tape. It is rp.commended that you always
volid in FILEDEF or LABELDEF to be sure the information
correct.
LABELDEF or eMS will be VOLl record
specify the
written is • Expiration date specification is always done in absolute form rather
than by retention period. You must always use the form yyddd where
yy is the year (O-99) and ddd the day (O-366). eMS does not handle
expiration dates specified by retention periods. • When eMS reads a HDRl label and finds an unexpired file, it always
issues a message allowing you to enter 'IGNORE' or 'ERROR'. 'ERROR' prevents opening the file but 'IGNORE' lets you ignore the error and
write over the unexpired file. • The NSL routine linkage is quite under CMS than in OS/VS. (See the section "NSL processing" fdr details.)
, • Volume serial number verification occurs every time a file on a tape
is opened under OS simulation unless the FILEtEF LEAVE option is used
for multifile tapes. • Existing VOLl labels are not automatically rewritten for density
incompatibility in CMS as they are in OS/VS. • HDR2 records are skipped for input under eMS for OS simulation. They
are not checked and information in them is not merged with DCB
information. HDR2 records are written (with information obtained
from the DCB) on output. • Blank tapes used for output in CMS cause the tape to run off the reel
if you define the tape file as SL or NL. The tape label processing
routines try to read an existing VOLl or HDRl label tefore writing on
the tape. Therefore, you should always use the eMS TAPE command to
write at least one tape mark (for NL tapes) or a VaLl label (for SL or SUL tapes) before using the tape to write an output data set. • If you specify a position parameter that is too big (that is, there
are not that many files on the tape), the tape will run off the reel
in CMS. 122.6 IBM VM/370 eMS Guide

Pg. of GC20-1819-2 Rev March 30, 1979 by Supp. SD23-9024-1 for 5748-XX8 • There are no user exits for user standard labels for EOV label
processing in CMS. • CMS does not support user return codes of 8 and 12 for input
user labels. If the return code from a user routine is
after input label processing, CMS treats it as if the return
4. (See the IBM publication Qs!s for details).
standard
not zero
code was or • No count is kept of user standard labels read or bypassed in CMS. If
more than eight such labels exist, the fact is not detected. • User label processing routines do not receive control under CMS when
an abend or a permanent I/O error occurs. • If a CMS output tape is not positioned at a HDR1 label or a tape mark
when label processing begins, error message 422 is issued. Under OS/VS such conditions cause an abend. • TCLOSE with the REREAD option causes a tape to be rewound under and then forward spaced one file if the tape has standard labels. Under OS/VS, the tape is backspaced four files and forward spaced one
file. REREAD for unlabelled tapes in eMS always causes a rewind.
For further information on OS/VS tape label processing, refer to the
fellowing IBM publications: and For details on end-of-tape/end-of-volume precessing under CMS, see
the "End-of-Volume" and "End-of-Tape processing" section later in this
publication.
LABEL PROCESSING IN CMS/DOS You specify the type of label processing you want in on a DTFMT macro in exactly the same way you specify it when you want to run your
program under DOS/VSE. See the Qyide for
details on eMS support for the DTFMT macro.
Labelled tapes are only supported if you use the DTFMT macro. There
is no support for labelled tapes in CMS/DOS for any other type. If yeu
try to read labelled tapes with a DTFCP or DTFDI macro, input standard IBM header labels are skipped, but no other input labels are processed. Output tapes with standard labels have these labels overwritten with a
tape mark. All tape work files are treated as output unlabelled files
in CMS/DOS although they are defined by a DTFMT. Tapes used for such
files have a tape mark written as the first record when the file is
opened. You define an unlabelled tape with the DTFMT parameter FILABL=NO. The
tape file is Frocessed as having no labels. You define a nonstandard labelled tape with the DTFMT parameter
FILABL=NSTD. You also must provide a routine to process your
nonstandard labels in the LABADDR=parameter of the DTFMT. TaFe processing in CMS for these files is the same as it is under DOS/VSE. Section 7. Using Real Printers, Punches, Readers, and Tapes 122.7