IBM Standard File Labels on Tape
IBM® standard file labels are 80 bytes long.
Each file has a header and a trailer label of the same format. This allows a tape to be read forward and backward.
- Header labels:
- HDR1 and HDR2 –
- At the beginning of a file.
- Trailer labels:
- EOF1 and EOF2 –
- At the end of a file.
- EOV1 and EOV2 –
- At the end of a volume and not the end of a file.
Data Set 2 Labels
To facilitate migration to an MVS™ environment, labeled output tapes that are created via DTFMT or DTFPH contain standard IBM data set label 2 records (HDR2, EOF2, EOV2). The purpose of these labels is to record characteristics of the file, such as block size, record size, record format. These labels also contain information about the recording technique used to create the file, the unit on which the data was written, and the job and program (taken from the COMREG) that were used to create the file. In an MVS environment, the file can thus be used without any data control block (DCB) or data definition (DD) specification.
Data set 2 labels are also created for standard labeled work files. On input, these labels are skipped.
Additional labels (HDR3 through HDR8, if present) are ignored by z/VSE.
Table 1 through Table 4 show IBM standard file labels for tapes.
Displ. | Length | Content |
---|---|---|
00 | 04 | Label ID: HDR1, EOF1, or EOV1. |
04 | 11 | File ID. From TLBL. |
15 | 06 | Volume serial number of first volume of the file. |
1B | 04 | Volume sequence number within the file. |
1F | 04 | File sequence number on the volume. |
23 | 04 | Version number of the file. |
27 | 02 | Subversion number. |
29 | 06 | Creation date: cyyddd. |
2F | 06 | Expiration date: cyyddd. |
35 | 01 | Reserved. |
36 | 06 | Number of blocks written. Used only in trailer labels. |
37 | 0D | System code: IBMDOSVS. |
49 | 01 | Bit 0 = 1: expiration date specified by retention period. |
4A | 02 | Reserved. |
4C | 04 | High-order block count. |
Displ. | Length | Content |
---|---|---|
00 | 04 | Label ID: HDR1, EOF1, or EOV1. |
04 | 11 | File ID. From TLBL. |
15 | 06 | Volume serial number of first volume of the file. |
1B | 04 | Volume sequence number within the file. |
1F | 04 | File sequence number within volume. |
23 | 04 | Version number of the file. |
27 | 02 | Subversion number. |
29 | 06 | Creation date: cyyddd. |
2F | 06 | Expiration date: cyyddd. |
35 | 01 | Data set security (accessibility character). |
36 | 06 | Number of blocks written. Used only in trailer labels. |
3C | 0D | System code: IBMZLB, followed by two blanks. |
49 | 07 | Reserved. |
Displ. | Length | Content |
---|---|---|
00 | 04 | Label ID: HDR2, EOF2, or EOV2. |
04 | 01 | Record format:
|
05 | 05 | Block length. |
0A | 05 | Record length. |
0F | 23 | Reserved. |
32 | 02 | Buffer-offset length. |
34 | 1C | Reserved. |
Displ. | Length | Content |
---|---|---|
00 | 04 | Label ID: HDR2, EOF2, or EOV2. |
04 | 01 | Record format:
|
05 | 05 | Block length, unpacked decimal (for DTFPH, a maximum block length of 32,767 is assumed). |
0A | 05 | Record length, unpacked decimal. |
0F | 01 | Tape density:
|
10 | 01 | Data set position:
Open sets the field to 0 when it is the first volume, that is, whenever the volume serial number and the file serial number are the same; otherwise it sets the field to 1. For end of volume (EOV) and close (EOF), the field is set to 0 or 1 in the same way as for Open. |
11 | 17 | Job/job step identification: Bytes 1 to 8: Job name (taken from the COMREG).
Byte 9: Set to '/'. Bytes 10 to 17: Program name (taken from the COMREG). For tape files that have been extended with TLBL DISP=OLD or DISP=MOD, this field in the EOV2/EOF2 labels contain the information that is related to the job and job step that extended the file. |
22 | 02 | Tape recording technique:
|
24 | 01 | Printer control character, always set to blanks. |
25 | 01 | Reserved for future use, set to blanks. |
26 | 01 | Block attribute.
|
27 | 02 | Reserved, set to blanks. |
29 | 06 | For the 3590 or 3592, bytes 42-47 contain the device serial number (taken from sense byte 27-29). |
2A | 05 | This field is set as follows:
|
2F | 01 | Checkpoint data set identifier, set to blanks. |
30 | 20 | Reserved, set to blanks. |