Imported Upstream version 0.72.4
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TANIGUCHI Takaki
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documentation/ru/qa36.html
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documentation/ru/qa36.html
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<head>
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<meta http-equiv="content-type" content="text/html; charset=UTF-8">
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<title>Remarks on read errors</title>
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<link rel="stylesheet" type="text/css" href="../include/dvdisaster.css">
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</head>
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<body>
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<!-- Title header -->
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<table width="100%" cellpadding="0" border="0">
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<tr>
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<td align="left">
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<span class="fxxl"><b>dvdisaster</b></span>
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<i>Версия 0.72.4 / 0.72 (pl4)</i>
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</td>
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<td align="right">
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<span class="fxxl"> </span><a href="http://dvdisaster.net/ru/">К интернет-версии</a>
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<a href="../cs/qa36.html"></a>
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<a href="../de/qa36.html"></a>
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<a href="../en/qa36.html"></a>
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</td>
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</tr>
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</table>
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<!-- Language chooser or separator -->
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<table width="100%" cellpadding="0" border="0">
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<tr>
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<td colspan="2" class="hsep"></td>
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</tr>
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<tr><td colspan="2" style="height: 10px">
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</td></tr>
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</table>
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<!-- Main body (Navigation, actual page content, optional news column) -->
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<table width="100%" cellspacing=0>
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<tr>
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<!-- Navigation -->
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<td style="background-color:#f0f0f0; vertical-align:top; width:20%;">
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<table width="100%" cellpadding="10">
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<tr>
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<td>
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<span class="fs"><b>Содержание</b></span>
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<table width="100%" cellpadding="0" cellspacing="0">
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<tr>
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<td class="hsep"></td>
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</tr>
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</table><p>
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<table width="100%">
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<tr><td colspan=3><span class="fs"><a href="news.html">Новости</a></span></td></tr>
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<tr><td></td><td></td><td style="height:10px;"></td></tr>
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<tr><td colspan=3><span class="fs"><a href="index.html">Обзор</a></span></td></tr>
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<tr><td></td><td></td><td style="height:10px;"></td></tr>
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<tr><td colspan=3><span class="fs"><a href="howtos.html">Howto's</a></span></td></tr>
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<tr><td></td><td></td><td style="height:10px;"></td></tr>
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<tr><td colspan=3><span class="fs"><a href="download.html">Скачать</a></span></td></tr>
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<tr><td></td><td></td><td style="height:10px;"></td></tr>
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<tr><td colspan=3><span class="fs"><a href="qa.html">Вопросы и ответы</a></span></td></tr>
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<tr><td style="width:1%; vertical-align:top;">·</td><td colspan=2><span class="fs"><a href="qa10.html">Технические вопросы</a></span></td></tr>
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<tr><td style="width:1%; vertical-align:top;">·</td><td colspan=2><span class="fs"><a href="qa20.html">Сообщения об ошибках</a></span></td></tr>
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<tr><td style="width:1%; vertical-align:top;">·</td><td colspan=2><span class="fs"><a href="qa30.html">Background information</a></span></td></tr>
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<tr><td></td><td style="vertical-align:top; font-size:small;">-</td><td><span class="fs"><a href="qa31.html">Error correction properties</a></span></td></tr>
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<tr><td></td><td style="vertical-align:top; font-size:small;">-</td><td><span class="fs"><a href="qa32.html">Image level data recovery</a></span></td></tr>
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<tr><td></td><td style="vertical-align:top; font-size:small;">-</td><td><span class="fs"><a href="qa33.html">RS01, RS02 and RS03</a></span></td></tr>
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<tr><td></td><td style="vertical-align:top; font-size:small;">-</td><td><span class="fs"><a href="qa34.html">Linear reading strategy</a></span></td></tr>
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<tr><td></td><td style="vertical-align:top; font-size:small;">-</td><td><span class="fs"><a href="qa35.html">Adaptive reading strategy</a></span></td></tr>
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<tr><td></td><td style="vertical-align:top; font-size:small;">-</td><td><span class="fs">Remarks on read errors</span></td></tr>
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<tr><td></td><td style="vertical-align:top; font-size:small;">-</td><td><span class="fs"><a href="qa37.html">Hints for storing the error correction files</a></span></td></tr>
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<tr><td></td><td></td><td style="height:10px;"></td></tr>
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<tr><td colspan=3><span class="fs"><a href="feedback.html">Сообщения об ошибках</a></span></td></tr>
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</table>
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</td>
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</tr>
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</table>
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</td>
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<td></td>
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<!-- Actual page contents -->
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<td style="vertical-align:top; width:77%;" rowspan="2">
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<!-- Insert actual page content below -->
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<h3 class="top">Remarks on read errors</h3>
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Optical media have their own error correction code which protects the data
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against small manufacturing errors and inaccuracies during writing.
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If the writer and medium are compatible and of high quality, the
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error correction built into the medium will at first be mainly idle.
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This leaves enough reserves to compensate normal wear and aging effects
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during many years of the medium usage.
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<p>
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When the capacity of the built-in error correction is finally exhausted,
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read errors will start to appear on the medium. These will be reported by
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the <a href="howtos10.html">"Scan"</a>-operation of dvdisaster.
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Depending on the time of first occurrence,
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two types of read errors are of particular interest:<p>
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<b>Read errors appearing right after writing the medium.</b>
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This is a sign of:
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<ul>
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<li>media from a faulty production run, or</li>
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<li>media which are not compatible with the writer.</li>
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</ul>
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A prudential choice is to dispose of the faulty media and
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to write the data on error-free media, possibly switching to a
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different producer.<p>
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Please withstand the temptation of trying to preserve
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the faulty media by means of an error correction file - this
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will most likely end with data loss.<p>
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<b>Read errors after a few months/years.</b>
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The built-in error correction of the medium will be increasingly loaded
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during its life time until it finally fails and read errors show up.
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This happens for mechanical reasons (scratches, warping of the plastic material)
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as well as for chemical causes (decaying dye and/or reflective layer).<p>
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These effects typically occur while the medium is stored away for a few months,
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and it may not be possible to read in all sectors afterwards.<p>
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Therefore it is crucial to create the
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<a href="howtos21.html">error correction data</a> in time.
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The ecc data contains information for recalculating the contents of
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missing sectors
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<a href="qa31.html">(within certain limits)</a>.
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Therefore with the help of the ecc data
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dvdisaster can recover images even if not all sectors
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could actually be read by the drive.<p>
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Since the error correction can reconstruct missing sectors up to a certain number,
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it is not necessary to squeeze out a defective medium for every readable sector.
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The <a href="qa35.html">adaptive reading strategy</a> checks during
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reading whether enough data for error correction has been collected.
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As soon as this is the case, reading stops and still unread sectors
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will be recovered using the ecc data.<p>
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<a name="reading-tips"><b>
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Some hints for effectively reading damaged media</b></a><p>
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The outcome from reading damaged media depends on several factors:
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<ul>
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<li><b>Not all drives are built the same.</b><br>
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Different drives have different reading capabilities.
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Take advantage of dvdisaster's function for completing an image
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with several reading passes and use different drives for each pass.
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Transfer the image file between computers using a network or rewritable media
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in order to use drives installed in different machines.
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<p></li>
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<li><b>Eject and insert the medium again.</b><br>
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Sometimes it makes a difference to eject the medium, turn it about a quarter,
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and then load it again for another reading pass.
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<p></li>
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<li><b>Some drives read better while being cold.</b><br>
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Turn off the computer over night and perform another reading attempt in the next
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morning.<p>
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But note: "Cold" refers to normal living room conditions - putting hardware
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or media into the fridge can be very unhealthy for them.<p></li>
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</ul>
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<!-- do not change below -->
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</td> <!-- end of page contents -->
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</tr>
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<!--
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<tr valign="bottom">
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<td style="background-color:#f0f0f0;">
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<table cellpadding="10"><tr><td><a href="http://dvdisaster.net/legacy/en/index.html"><span class="fs"></span></a></td></tr></table>
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</td>
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<td></td>
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<td></td>
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</tr>
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-->
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</table> <!-- end of main body table -->
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<!-- Page footer -->
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<table width="100%" cellpadding="0" border="0">
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<tr><td colspan="2" style="width:100%; height:10px;"></td>
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</tr>
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<tr><td colspan="2" class="hsep"></td>
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</tr>
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<tr>
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<td align="center">
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<span class="fs">
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<i> Copyright 2007-2009 Igor Gorbounov.<br>
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Дословное копирование и распространение всей этой статьи разрешается на любом носителе, при условии, что это уведомление сохраняется.
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</i>
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</span>
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</td>
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||||
</tr>
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||||
<tr><td colspan="2" class="hsep"></td>
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</tr>
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</table>
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</body>
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</html>
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