<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en" dir="ltr"> <head> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> <meta name="keywords" content="Intel Partition Table,TestDisk" /> <link rel="shortcut icon" href="favicon.ico" /> <link rel="search" type="application/opensearchdescription+xml" href="opensearch_desc.php" title="CGSecurity (English)" /> <link rel="copyright" href="http://www.gnu.org/copyleft/fdl.html" /> <title>Intel Partition Table - CGSecurity</title> <style type="text/css" media="screen, projection">/*<![CDATA[*/ @import "shared.css_97.css"; @import "main.css_97.css"; /*]]>*/</style> <link rel="stylesheet" type="text/css" media="print" href="commonprint.css_97.css" /> <!--[if lt IE 5.5000]><style type="text/css">@import "ie50fixes.css_97.css";</style><![endif]--> <!--[if IE 5.5000]><style type="text/css">@import "ie55fixes.css_97.css";</style><![endif]--> <!--[if IE 6]><style type="text/css">@import "ie60fixes.css_97.css";</style><![endif]--> <!--[if IE 7]><style type="text/css">@import "ie70fixes.css_97.css";</style><![endif]--> <!--[if lt IE 7]><script type="text/javascript" src="iefixes.js_97"></script> <meta http-equiv="imagetoolbar" content="no" /><![endif]--> <script type= "text/javascript">/*<![CDATA[*/ var skin = "monobook"; var stylepath = "/mw/skins"; var wgArticlePath = "/wiki/$1"; var wgScriptPath = "/mw"; var wgScript = "/mw/index.php"; var wgServer = "http://www.cgsecurity.org"; var wgCanonicalNamespace = ""; var wgCanonicalSpecialPageName = false; var wgNamespaceNumber = 0; var wgPageName = "Intel_Partition_Table"; var wgTitle = "Intel Partition Table"; var wgAction = "view"; var wgRestrictionEdit = []; var wgRestrictionMove = []; var wgArticleId = "1308"; var wgIsArticle = true; var wgUserName = null; var wgUserGroups = null; var wgUserLanguage = "en"; var wgContentLanguage = "en"; var wgBreakFrames = false; var wgCurRevisionId = "1501"; /*]]>*/</script> <script type="text/javascript" src="wikibits.js_97"><!-- wikibits js --></script> <script type="text/javascript" src="http://www.cgsecurity.org/mw/index.php?title=-&action=raw&gen=js&useskin=monobook"><!-- site js --></script> <style type="text/css">/*<![CDATA[*/ @import "Common.css"; @import "Monobook.css"; @import "dyn.css"; /*]]>*/</style> <!-- Head Scripts --> <script type="text/javascript" src="ajax.js_97"></script> </head> <body class="mediawiki ns-0 ltr page-Intel_Partition_Table"> <div id="globalWrapper"> <div id="column-content"> <div id="content"> <a name="top" id="top"></a> <h1 class="firstHeading">Intel Partition Table</h1> <div id="bodyContent"> <h3 id="siteSub">From CGSecurity</h3> <div id="contentSub"></div> <div id="jump-to-nav">Jump to: <a href="#column-one">navigation</a>, <a href="#searchInput">search</a></div> <!-- start content --> <a name="How_is_the_Partition_Table_written_.3F"></a><h2> <span class="mw-headline"> How is the Partition Table written ? </span></h2> <p>CHS (Cylinder, Head, Sector) values are limited by a set number of bits for each value in the 16-byte partition table entries to: 1023,254,63. So LBA and CHS values can't be equal for HD bigger than 8GB. </p><p>There are two ways to store the CHS value: </p> <ul><li>first way </li></ul> <pre> convert LBA to CHS, store (cylinder & 0x3FF, head & 0xFF, sector & 0x3F) </pre> <p>It's what Partition Magic does (prior to version 8.0?). </p> <ul><li>second way </li></ul> <pre> convert LBA to CHS if cylinder <= 1023, store (cylinder & 0x3FF, head & 0xFF, sector & 0x3F) else store (1023, max_head & 0xFF, max_sector & 0x3F) </pre> <p>This is what Linux fdisk and TestDisk do. </p><p><br /> </p><p>When TestDisk checks the partition table, it considers both ways may be correct. But the second way is better because start CHS is always lower or equal to end CHS. </p><p><br /> Example: A hard disk's logical geometry is 255 heads per cylinder and 63 sectors per head. A partition begins at LBA=46781280 or CHS=2912,0,1. This partition ends at 3072,254,63. </p> <ul><li>First way: </li></ul> <pre> start: 864, 0, 1 end: 0,254,63 </pre> <ul><li>Second way: </li></ul> <pre> start: 1023,254,63 end: 1023,254,63 </pre> <p><br /> NB: 1023 = 0x3FF (1023*255+254)*63+63-1=16450559 (2912*255+ 0)*63+ 1-1=46781280 </p><p>Partition Magic (before version 8.0?) considered the second way as invalid; even though it's an agreed upon standard. 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