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<h1 class="topictitle1">ISO/ANSI standard data set label 2 (HDR2/EOV2/EOF2)</h1>
<div><p>The ISO/ANSI standard data set label 2 (HDR2/EOV2/TRL2) is 80 characters
in length and is used to identify additional information about the data set.
The system records the data set label in ASCII.</p>
<div class="tablenoborder"><table cellpadding="4" cellspacing="0" summary="" width="100%" frame="hsides" border="0" rules="none"><caption>Table 1. Format of the IBM<sup>®</sup> Standard Data
Set Label 2 (HDR2/EOV2/EOF2)</caption><thead align="left"><tr><th align="left" valign="bottom" width="9.945750452079565%" id="d0e25">Offset</th>
<th align="left" valign="bottom" width="14.466546112115733%" id="d0e27">Data type</th>
<th align="left" valign="bottom" width="10.849909584086799%" id="d0e29">Length</th>
<th align="left" valign="bottom" width="64.73779385171791%" id="d0e31">Contents</th>
</tr>
</thead>
<tbody><tr><td align="left" valign="top" width="9.945750452079565%" headers="d0e25 ">0</td>
<td align="left" valign="top" width="14.466546112115733%" headers="d0e27 ">Character</td>
<td align="left" valign="top" width="10.849909584086799%" headers="d0e29 ">3</td>
<td align="left" valign="top" width="64.73779385171791%" headers="d0e31 ">Label identifier</td>
</tr>
<tr><td align="left" valign="top" width="9.945750452079565%" headers="d0e25 ">3</td>
<td align="left" valign="top" width="14.466546112115733%" headers="d0e27 ">Character</td>
<td align="left" valign="top" width="10.849909584086799%" headers="d0e29 ">1</td>
<td align="left" valign="top" width="64.73779385171791%" headers="d0e31 ">Label number</td>
</tr>
<tr><td align="left" valign="top" width="9.945750452079565%" headers="d0e25 ">4</td>
<td align="left" valign="top" width="14.466546112115733%" headers="d0e27 ">Character</td>
<td align="left" valign="top" width="10.849909584086799%" headers="d0e29 ">1</td>
<td align="left" valign="top" width="64.73779385171791%" headers="d0e31 ">Record Format</td>
</tr>
<tr><td align="left" valign="top" width="9.945750452079565%" headers="d0e25 ">5</td>
<td align="left" valign="top" width="14.466546112115733%" headers="d0e27 ">Character</td>
<td align="left" valign="top" width="10.849909584086799%" headers="d0e29 ">5</td>
<td align="left" valign="top" width="64.73779385171791%" headers="d0e31 ">Block Length</td>
</tr>
<tr><td align="left" valign="top" width="9.945750452079565%" headers="d0e25 ">10</td>
<td align="left" valign="top" width="14.466546112115733%" headers="d0e27 ">Character</td>
<td align="left" valign="top" width="10.849909584086799%" headers="d0e29 ">5</td>
<td align="left" valign="top" width="64.73779385171791%" headers="d0e31 ">Record Length</td>
</tr>
<tr><td align="left" valign="top" width="9.945750452079565%" headers="d0e25 ">15</td>
<td align="left" valign="top" width="14.466546112115733%" headers="d0e27 ">Character</td>
<td align="left" valign="top" width="10.849909584086799%" headers="d0e29 ">35</td>
<td align="left" valign="top" width="64.73779385171791%" headers="d0e31 ">Reserved for Operating System</td>
</tr>
<tr><td align="left" valign="top" width="9.945750452079565%" headers="d0e25 ">50</td>
<td align="left" valign="top" width="14.466546112115733%" headers="d0e27 ">Character</td>
<td align="left" valign="top" width="10.849909584086799%" headers="d0e29 ">2</td>
<td align="left" valign="top" width="64.73779385171791%" headers="d0e31 ">Buffer offset</td>
</tr>
<tr><td align="left" valign="top" width="9.945750452079565%" headers="d0e25 ">52</td>
<td align="left" valign="top" width="14.466546112115733%" headers="d0e27 ">Character</td>
<td align="left" valign="top" width="10.849909584086799%" headers="d0e29 ">28</td>
<td align="left" valign="top" width="64.73779385171791%" headers="d0e31 ">Reserved</td>
</tr>
</tbody>
</table>
</div>
<p>The manual describes the contents and function of each of the following
fields.</p>
<ul><li>Label identifier <div class="p">The characters identify the type of data set label.
<dl><dt class="dlterm">HDR</dt>
<dd>Header Label (the beginning of a data set)</dd>
<dt class="dlterm">EOF</dt>
<dd>Trailer Label (the end of a data set)</dd>
<dt class="dlterm">EOV</dt>
<dd>Trailer Label (the end of a data set that is continued on another volume)</dd>
</dl>
</div>
</li>
<li>Label number <p>The relative position of this label within the set of
labels of the same type; it is always 2 for the data set label 2.</p>
</li>
<li>Record Format <div class="p">An alphabetic character that indicates the format of
the records in the data set. The record format indicates to the operating
system how to interpret the blocks of data that the program reads from the
tape volume. <dl><dt class="dlterm">F</dt>
<dd>Fixed length records</dd>
<dt class="dlterm">V</dt>
<dd>Variable length records</dd>
<dt class="dlterm">U</dt>
<dd>Undefined length records</dd>
</dl>
</div>
</li>
<li>Block Length <p>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 2048.
This block length should include the buffer offset and padding.</p>
<p>Note
that the 18-byte to 2048 byte limit on block length is an ISCII/ASCII standard.
You can specify larger blocks (up to 9999 bytes) with the agreement of the
interchange parties. However, for tapes with Version 3 labels, exceeding the
2048 byte limit might create incompatible tapes.</p>
<div class="p">Interpretation of
the number depends on the associated record format field as follows: <dl><dt class="dlterm">Record format F</dt>
<dd>Maximum block length.</dd>
<dt class="dlterm">Record format D</dt>
<dd>Maximum block length that includes the 4 byte length indicator in the
records and the optional block prefix.</dd>
<dt class="dlterm">Record format S</dt>
<dd>Maximum block length that includes the optional block prefix, plus one
or more pairs of 5 byte segment control words and segments.</dd>
</dl>
</div>
</li>
<li>Record Length <div class="p">A number indicating the record length, in bytes, of
the logical records on the tape volume. The interpretation of the number depends
on the Record Format field. <ul><li>Record format F <p>Actual record length</p>
</li>
<li>Record format D <p>Maximum record length that includes the 4 byte length
indicator in the records</p>
</li>
<li>Record format S <p>Maximum record length that excludes all the 5 byte
segment control words that describe the record. If the record length is larger
than 99999, this field is 0.</p>
</li>
</ul>
</div>
</li>
<li>Reserved for Operating System <div class="p">The content of this field is optional
for each operating system. <span class="keyword">i5/OS™</span> has
chosen similar meaning to the same bytes in the IBM Standard Data Set Label 2. <ul><li>Tape Density (1 byte) <dl><dt class="dlterm">3</dt>
<dd>1600 bpi</dd>
<dt class="dlterm">4</dt>
<dd>3200 bpi</dd>
<dt class="dlterm">5</dt>
<dd>6250 bpi</dd>
<dt class="dlterm">blank</dt>
<dd>All other densities/formats</dd>
</dl>
</li>
<li>Data Set Position (1 byte) <div class="p">A code indicating a volume switch is as
follows: <dl><dt class="dlterm">0</dt>
<dd>No volume switch has occurred</dd>
<dt class="dlterm">1</dt>
<dd>A volume switch previously occurred</dd>
</dl>
</div>
</li>
<li>Job/Job Step Identification (17 bytes) <p>This field identifies the job
and job step that created or extended the data set. <span class="keyword">i5/OS</span> does not use this field.</p>
</li>
<li>Tape Recording Technique (2 bytes) <div class="p">This field indicates the tape recording
technique used in creating the data set. <dl><dt class="dlterm">blank</dt>
<dd>No Improved Data Recording Capability (IDRC) used.</dd>
<dt class="dlterm">'P '</dt>
<dd>Improved Data Recording Capability (IDRC) used.</dd>
</dl>
</div>
</li>
<li>Control Character (1 byte) <div class="p">A printer control code indicating whether
the program uses a control character set to create the data set and the type
of control characters the program uses: <dl><dt class="dlterm">A</dt>
<dd>Contains ISO/ANSI control letters</dd>
<dt class="dlterm">blank</dt>
<dd>Contains no control characters</dd>
</dl>
</div>
</li>
<li>Buffer Alignment Block (1 byte) <p><span class="keyword">i5/OS</span> does not use this field.</p>
</li>
<li>Block Attribute <div class="p">A code indicating the block attribute used to create
the data set: <dl><dt class="dlterm">B</dt>
<dd>Blocked records</dd>
<dt class="dlterm">blank</dt>
<dd>Records not blocked</dd>
</dl>
</div>
</li>
<li>Reserved (11 bytes) <p><span class="keyword">i5/OS</span> does not use this field.</p>
</li>
</ul>
</div>
</li>
<li>Buffer Offset <p>The length of the block prefix (from 0 to 99). Used
to determine the length of an optional prefix that might be a part of a physical
block on tape. The version of the prefix for variable and spanned record formats
is known as a block descriptor word (BDW). A BDW is always 4 bytes long and
contains the block length of the physical record it describes, including the
BDW.</p>
</li>
</ul>
</div>
<div>
<div class="familylinks">
<div class="parentlink"><strong>Parent topic:</strong> <a href="volum.htm" title="This topic describes the volume labels used in the open feedback area.">Volume label fields</a></div>
</div>
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