User's Manual

IBM OS/360 AND DOS/360 STANDARD LABELED TAPES
XEROX LASER PRINTING SYSTEMS TAPE FORMATS MANUAL 2-7
The HDR1 label is always the first beginning-of-file label. When the
file is the first on the tape, the HDR1 label immediately follows the last
VOL label without an intervening tape mark. When the file is not the
first on the tape, HDR1 is the first block following the tape mark that
followed the previous end-of-file label group. The HDR1 label is
created by both OS/360 and DOS/360.
The EOV1 label is always the first (or only) label following the last
data block on a tape when a file is continued on a succeeding tape.
It is separated from the final data block by a tape mark.
The EOF1 label is always the first (or only) label following the last
data block of a file. It is separated from the final data block by a tape
mark.
HDR2, EOV2, EOF2 labels
The formats of these labels are identical and are described in table
2-5. Only HDR2 labels are processed. EOV2 and EOF2 are
bypassed.
Table 2- 5. HDR2, EOV2, and EOF2 labels (IBM tapes)
Name
Character
position(s)
Field Description
Label identifier 1-3 1 This is the 3-character identifier HDR, EOV, or EOF.
Label number 4 2 This is the number 2.
Record format* 5 3 This is an alphabetic character that indicates the
format of the records in the associated file. The
characters are:
F = fixed length.
V = variable length.
U = undefined length.
Block length* 6-10 4 This is a binary number (up to 32,764) that indicates
the block length in bytes.
Format F—Must be an integral multiple of record
length (field 5).
Format V—Indicates maximum block length in file,
including the 4-byte length field.
Format U—Indicates maximum block length.
Record length* 11-15 5 This is a number that indicates record length in bytes.
Format F—Indicates actual record length.
Format V—Indicates maximum record length in file,
including the 4-byte length field.
Format U—Zeros.
Tape density 16 6 This is a code that indicates the recording density of
the tape.
2 = 800 bpi
3 = 1600 bpi
* Fields 3, 4, 5, and 12 are used by the operating system.