Data set header labels

ISO/ANSI header labels consist of a data set label 1 (HDR1) and, generally, a data set label 2 (HDR2). The HDR1 label is created by the system routines each time a data set is recorded on tape. A HDR1 label identifies and describes the data set and protects it from unauthorized use.

The HDR1 label is 80 characters long. Any characters after position 80 are not used for label checking or verification.

A HDR2 label is optional for ISO/ANSI labeled tapes. When present, it immediately follows the HDR1 label. The z/OS operating system produces a HDR2 label for output tapes; such a label on an input tape is treated similarly to an IBM HDR2 label. If the HDR2 label is produced by another system, the "reserved for operating system" fields are not processed.

Labels identified as HDR3 - HDR9 are allowed but only checked for valid label identification and correct sequencing (and only if they are among the header labels of a requested data set). z/OS does not create optional data set header labels beyond the second label.