Figure 1 shows the format of UHL and
UTL labels.
Figure 1. Format of ISO/ANSI user labels
1—Label Identifier (3 bytes)
- Contents: Three characters that identify the label are
as follows:
-
- UHL
- User header label (at the beginning of a data set)
- UTL
- User trailer label (at the end-of-volume or end-of-data set).
- Processing: This field is read to verify that the record
is a user label. The system accepts either UHL or UTL.
2—Label Number (1 byte)
- Contents: Any valid Version 3 or Version 4 character.
- Processing: This field is checked by the operating system
for a valid Version 3 or Version 4 character during creation of a
user header label (UHL) during open/EOV if validation has not been
suppressed. If an invalid character is detected, the label validation
exit is entered.
- Difference from IBM Field: This field can contain only
numeric 1 to 8 for IBM standard user labels. A maximum of 8 user header
or trailer labels is supported for conventional IBM standard user
labels, but any number of user labels can be written for Version 3
or Version 4 tapes, and they may be lettered or numbered in any order.
3—User Specified (76 bytes)
- Contents: Specified by the user, but must be valid Version
3 or Version 4 characters.
- Processing: Specified in the DCB exit list. This field
is checked as explained for Field 2.