Introduction to tape processing

Labels are used to identify magnetic tape volumes and the data sets on those volumes. The term "volume" applies to reels, which are round, and to cartridges, which are rectangular. See Cartridge label. In this book the term "data set" is synonymous with "file." That is not true in all z/OS books. You can process tape volumes with the following labels:
  • IBM standard labels
  • Labels that follow standards published by:
    • International Organization for Standardization (ISO)
    • American National Standards Institute (ANSI)
  • Nonstandard labels
  • No labels
Your installation can install a bypass for any type of label processing; however, the use of labels is recommended as a basis for efficient control of your tape volumes. The operating system performs label processing and most tape positioning. Unlike many operating systems, application programs on z/OS generally do not perform these functions. Therefore, application programs can be device-independent.
IBM standard tape labels consist of volume labels and groups of data set labels. The volume label, identifying the volume and its owner, is the first record on the tape. The data set label, identifying the data set and describing its contents, precede and follow each data set on the volume:
  • The data set labels that precede the data set are called header labels.
  • The data set labels that follow the data set are called trailer labels. They are almost identical to the header labels.
  • The data set label groups can include standard user labels at your option.

Usually, the formats of ISO and ANSI labels, which are defined by the respective organizations, are similar to the formats of IBM standard labels. Unless otherwise specified, the term standard label, as used in this manual, refers to IBM, ISO, and ANSI standard labels. However, whereas ISO and ANSI labeled tapes are coded in the American National Standard Code for Information Interchange (ASCII), IBM labeled tapes are coded either in the extended binary-coded-decimal interchange code (EBCDIC) or in binary-coded-decimal interchange code (BCDIC).

Nonstandard tape labels can have any format and are processed by routines that the installation provides. Unlabeled tapes contain only data sets and tape marks.

Figure 1 shows the IBM standard, ISO and ANSI standard, nonstandard, and unlabeled tape layouts for a single data set on a single volume. Detailed layouts and variations for each type are illustrated and described in the appropriate sections of this manual.

Tape volumes with standard tape labels may be defined to Resource Access Control Facility (RACF), a component of the SecureWay Security Server for z/OS, by volume serial under the TAPEVOL class of entities. RACF authorization checking is performed for every standard labeled tape if system-wide tape protection has been specified. No protection is specifically extended by the system to nonstandard labeled tapes, but the installation-written nonstandard tape label routines may provide such protection.

Figure 1. Basic tape layouts
Basic tape layouts