The volume label group immediately follows the first two initial program loading (IPL) records on track 0 of cylinder 0 of the volume. It consists of the initial volume label at record 3 plus a maximum of seven additional volume labels. The initial volume label identifies a volume and its owner, and is used to verify that the correct volume is mounted. It can also be used to prevent use of the volume by unauthorized programs. The additional labels can be processed by an installation routine that is incorporated into the system.

The format of the data portion of the direct access volume label group is shown in Figure 1.

Figure 1. Initial Volume Label Format

The operating system identifies an initial volume label when, in reading the initial record, it finds that the first 4 characters of the record are VOL1. That is, they contain the volume label identifier and the volume label number. The initial volume label is 80 bytes. The format of an initial volume label are described in the following text.

Volume Label Identifier (VOL). Field 1 identifies a volume label.

Volume Label Number (1). Field 2 identifies the relative position of the volume label in a volume label group. It must be written as X'F1'.

Volume Serial Number. Field 3 contains a unique identification code assigned when the volume enters the system. You can place the code on the external surface of the disk drive for visual identification. The code is any 1 to 6 alphanumeric or national (#, $, @) characters, or a hyphen (X'60'). If this field is fewer than 6 characters, it is padded on the right with blanks.

Volume Security. Field 4 is reserved for use by installations that want to provide security for volumes. Make this field an X'C0' unless you have your own security processing routines.

VTOC Pointer. Field 5 of direct access volume label 1 contains the address of the VTOC in the form of CCHHR.

Reserved. Field 6 is reserved for possible future use, and should be left blank.

Owner Name and Address Code. Field 7 contains an optional identification of the owner of the volume.

Reserved. Field 8 is reserved for possible future use, and should be left blank.

Dump conditioning volume serial number. Field 9 contains the volume serial number of the volume that the dump conditioned volume was copied from. This field contains blanks when the volume is not a dump conditioned volume.

Reserved. Field 10 is reserved and should be left blank.

Volume label flag area. Field 11 contains volume label flags. Bit 0 (X'80') being set to 1 indicates it is an XRC logger volume. This field contains a blank when the volume is not an XRC logger volume.

Reserved. Field 12 is reserved for possible future use, and should be left blank.

Label standard version. Field 13 contains the version of the label.