Format of the IBM standard volume label (VOL1)

The IBM standard volume label (VOL1) is 80 characters in length and is used to identify the tape volume and its owner. It is always the first record on an IBM standard labeled tape. It is recorded in EBCDIC on 9-track tape units, or in BCDIC on 7-track tape units.

Figure 1 shows the format of the volume label. The shaded areas represent fields that are recorded in the label, but are not used or verified during processing. The contents and processing of each field of the label are described below. The processing descriptions refer to the following system control blocks:

Job file control block (JFCB)
Unit control block (UCB)

Figure 1. Format of IBM standard volume label

1—Label Identifier (3 bytes)

Contents: The characters VOL identify this label as a volume label.
Processing: This field is read to verify that a standard labeled tape is mounted, and that this label is a volume label.
The labels can be initially created by the IEHINITT utility program, the DFSMSrmm-supplied EDGINERS utility program, and under certain circumstances during Open/EOV processing.

For standard labeled tape volume requests, DFSMSrmm or the label anomaly installation exit routine or label editor installation exit can give permission for the OPEN or EOV routines to write or rewrite the VOL1 label. See IBM standard volume label editor routines for more information.

2—Label Number (1 byte)

Contents: The relative position of this label within a set of labels of the same type; it is always 1 for the IBM standard volume label.
Processing: Verified in conjunction with Field 1 to identify this label as VOL1.

3—Volume Serial Number (6 bytes)

Contents: A unique identification code that is assigned through DFSMSrmm or IEHINITT to the volume when it enters the system, or that is assigned by the operator when the Open or EOV routines label the volume. This code may also appear on the external surface of the volume for visual identification. The code is normally numeric characters (000000 to 999999), but may be any 6 alphanumeric characters. It may be from 1 to 6 characters, but, if fewer than 6 characters, the code must be left-justified, and the remainder is padded with blanks.
If the volume serial number is specified in the JCL statements, all national characters, the hyphen, and other special characters are accepted when enclosed in apostrophes. Their use is not recommended, however, because it can be difficult to recognize volume serial numbers when typewriter heads, print chains, and screen fonts with nonalphanumeric characters are used.

If the volume serial number is assigned through the IEHINITT utility program, A through Z, 0 through 9, and the hyphen are the only valid characters that may be specified.

In a tape library there is an additional restriction. See System-Managed mountable tape external labels.
Processing: When the user specifies a volume serial number, it is in the JFCB. The system copies it to the UCB. When the system processes the labels, it compares the number in the UCB to the number in this field of the label to ensure that the correct volume is mounted.
For scratch output tapes, the volume serial number is obtained from this field of the label and recorded in both the JFCB and the UCB.

The EDGINERS and IEHINITT utility programs can create this label with a volume serial number of up to 6 characters. The number is left-justified, and the remainder of this field is padded with blanks.

4—Reserved (1 byte)

Contents: Reserved for possible future use—initialized as a blank or zero.
Processing: Not used.

5—VTOC Pointer (5 bytes)

Contents: Direct access volumes only. This field is not used for tape volumes and should be recorded as blanks.
Processing: Not used or verified. The EDGINERS and IEHINITT utility programs write blanks in this field.

6—Reserved (25 bytes)

Contents: Reserved for possible future use—should be recorded as blanks. The EDGINERS and IEHINITT utility programs write blanks in this field. The IEHINITT utility program writes blanks in this field.
Historical note: In certain levels of MVS/DFP™ Version 3, position 36 may have been written as "P" to signify that the data was compacted using IDRC. The system no longer does this.

7—Owner Name and Address Code (10 bytes)

Contents: Indicates a specific customer, person, installation, department, and so forth, to which the volume belongs. Any code or name is acceptable.
Processing: Not used or verified. The EDGINERS and IEHINITT utility programs write the text specified by the user, and the open and EOV routines write the text specified by the operator. If the code is less than 10 bytes, it is left-justified and the remainder of the field is padded with blanks. EDGINERS and IEHINITT allows EBCDIC alphanumeric and special characters.

8—Reserved (29 bytes)

Contents: Reserved for possible future use—should be recorded as blanks.
Processing: Not used or verified. The EDGINERS and IEHINITT utility programs write blanks in this field.