The IBM® standard
data set label 2 (HDR2/EOV2/TRL2) is 80 characters in length and the program
uses it to identify additional information about the data set.
Table 1. Format of the IBM Standard Data
Set Label 2 (HDR2/EOV2/EOF2)| Offset |
Data type |
Length |
Contents |
|---|
| 0 |
Character |
3 |
Label identifier |
| 3 |
Character |
1 |
Label number |
| 4 |
Character |
1 |
Record Format |
| 5 |
Character |
5 |
Block Length |
| 10 |
Character |
5 |
Record Length |
| 15 |
Character |
1 |
Tape Density/Format |
| 16 |
Character |
1 |
Data Set Position |
| 17 |
Character |
17 |
Job/Job Step Identification |
| 34 |
Character |
2 |
Tape Recording Technique |
| 36 |
Character |
1 |
Control Character |
| 37 |
Character |
1 |
Reserved |
| 38 |
Character |
1 |
Block Attribute |
| 39 |
Character |
3 |
Reserved |
| 42 |
Character |
5 |
Device Serial Number (not used) |
| 47 |
Character |
1 |
Checkpoint Data Set Identifier |
| 48 |
Character |
22 |
Reserved |
| 70 |
Character |
10 |
Large Block Length |
The program records the data set label in EBCDIC.
The program describes the contents and function of each of the following
fields.
- Label identifier
The characters identify the type of data set label.
- HDR
- Header Label (the beginning of a data set)
- EOF
- Trailer Label (the end of a data set)
- EOV
- Trailer Label (the end of a data set that is continued on another volume)
- Label number
The relative positions of this label within the set of
labels of the same type. The Label number is always 2 for the IBM data set label
2.
- Record Format
An alphabetic character that indicates the format of
the records in the data set. While the operating system reads from the tape,
the Record format field tells the operating system how to interpret the blocks
of data the program reads.
- F
- Fixed length records
- V
- Variable length records
- U
- Undefined length records
- Block Length
A number indicating the block length (in bytes) of the
data blocks on the tape. The number in this field can range from 18 to 32 767
on i5/OS™.
For numbers greater than 32 767, the Large Block Length field allows
values up to 512 KB.
- Record Length
A number that indicates the record length, in bytes,
of the logical records on the tape volume. The interpretation of the number
depends on the Record Format field.
- F
- Fixed length records.
- V
- Variable length records.
- U
- Undefined length records
- Tape Density/Format
A code indicating the record density/format of
the tape volume.
- 3
- 1600 bpi
- 4
- 6250 bpi
- 5
- 3200 bpi
- blank
- all other densities/formats
- Data Set Position
A code indicating a volume switch is as follows:
- 0
- No volume switch has occurred
- 1
- A volume switch previously occurred
- Job/Job Step Identification
This field identifies the job and job
step that created or extended the data set. i5/OS does not use this field.
- Tape Recording Technique
This field indicates the tape recording technique
used in creating the data set.
- blank
- No Improved Data Recording Capability (IDRC) used.
- 'P '
- Improved Data Recording Capability (IDRC) used.
- Control Character
A printer control code indicating whether the program
uses a control character set to create the data set and the type of control
characters used:
- A
- Contains ANSI control characters
- M
- Contains machine control characters
- blank
- Contains no control characters
- Block Attribute
A code indicating the block attribute used to create
the data set:
- B
- Blocked records
- S
- Spanned records, if the record format byte is V
- S
- Standard records, if the record format byte is F
- R
- Blocked and spanned records, if the record format byte is V
- R
- Blocked and standard records, if the record format byte is F
- blank
- Records that are not blocked and not spanned, or records that are not
blocked and not standard
- Device Serial Number (not used)
The serial number of the device that
writes the volume. Header and trailer labels can have different serial numbers
if the program extends the data set. i5/OS does not use this field.
- Checkpoint Data Set Identifier
This byte contains the character C
if the data set is a secure checkpoint data set. The byte is blank if the
data set is not a secure data set checkpoint.
- Large Block Length
A number indicating the block length (in bytes)
of the data blocks on the tape. The number in this field can range from 18
to 524288 on i5/OS.
For numbers up to 32767, the Block Length field also contains the block length
in bytes.