User header and trailer label groups can be included with data sets of physically sequential or direct organization. They are not supported for extended format data sets. The labels in each group have the format shown in Figure 1.

Figure 1. User Header and Trailer Labels on DASD or Tape

Each group can include as many as eight labels, but the space required for both groups must not be more than one track on a direct access storage device. A program becomes device-dependent (among direct access storage devices) when it creates more than eight header labels or eight trailer labels.

If user labels are specified in the DD statement (LABEL=SUL), an additional track is normally allocated when the data set is created. No additional track is allocated when specific tracks are requested (SPACE=(ABSTR,...)). In that case, labels are written on the first track that is allocated.

User Header Label Group. The operating system writes these labels as directed by the processing program recording the data set. The first four characters of the user header label must be UHL1,UHL2, through UHL8; you can specify the remaining 76 characters. When the data set is read, the operating system makes the user header labels available to the application program for processing.

User Trailer Label Group. These labels are recorded (and processed) as explained in the preceding text for user header labels, except that the first four characters must be UTL1,UTL2, through UTL8.

The format of user header and trailer labels follows:

Label Identifier. Field 1 shows the kind of user header label. “UHL” means a user header label; “UTL” means a user trailer label.

Label Number. Field 2 identifies the relative position (1 to 8) of the label within the user label group. It is an EBCDIC character.

User-Specified. Field 3 (76 bytes).