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vector-toc-level-2"> <a class="vector-toc-link" href="#Implementations"> <div class="vector-toc-text"> 1.2 Implementations </div> </a> <ul id="toc-Implementations-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Architectural_features" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Architectural_features"> <div class="vector-toc-text"> 1.3 Architectural features </div> </a> <ul id="toc-Architectural_features-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Virtual_address_space_details" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Virtual_address_space_details"> <div class="vector-toc-text"> 1.4 Virtual address space details </div> </a> <ul id="toc-Virtual_address_space_details-sublist" class="vector-toc-list"> <li id="toc-Canonical_form_addresses" class="vector-toc-list-item vector-toc-level-3"> <a class="vector-toc-link" href="#Canonical_form_addresses"> <div class="vector-toc-text"> 1.4.1 Canonical form addresses </div> </a> <ul id="toc-Canonical_form_addresses-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Page_table_structure" class="vector-toc-list-item vector-toc-level-3"> <a class="vector-toc-link" href="#Page_table_structure"> <div class="vector-toc-text"> 1.4.2 Page table structure </div> </a> <ul id="toc-Page_table_structure-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Operating_system_limits" class="vector-toc-list-item vector-toc-level-3"> <a class="vector-toc-link" href="#Operating_system_limits"> <div class="vector-toc-text"> 1.4.3 Operating system limits </div> </a> <ul id="toc-Operating_system_limits-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Physical_address_space_details" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Physical_address_space_details"> <div class="vector-toc-text"> 1.5 Physical address space details </div> </a> <ul id="toc-Physical_address_space_details-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Operating_modes" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Operating_modes"> <div class="vector-toc-text"> 1.6 Operating modes </div> </a> <ul id="toc-Operating_modes-sublist" class="vector-toc-list"> <li id="toc-Long_mode" class="vector-toc-list-item vector-toc-level-3"> <a class="vector-toc-link" href="#Long_mode"> <div class="vector-toc-text"> 1.6.1 Long mode </div> </a> <ul id="toc-Long_mode-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Legacy_mode" class="vector-toc-list-item vector-toc-level-3"> <a class="vector-toc-link" href="#Legacy_mode"> <div class="vector-toc-text"> 1.6.2 Legacy mode </div> </a> <ul id="toc-Legacy_mode-sublist" class="vector-toc-list"> <li id="toc-Protected_mode" class="vector-toc-list-item vector-toc-level-4"> <a class="vector-toc-link" href="#Protected_mode"> <div class="vector-toc-text"> 1.6.2.1 Protected mode </div> </a> <ul id="toc-Protected_mode-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Real_mode" class="vector-toc-list-item vector-toc-level-4"> <a class="vector-toc-link" href="#Real_mode"> <div class="vector-toc-text"> 1.6.2.2 Real mode </div> </a> <ul id="toc-Real_mode-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> </ul> </li> </ul> </li> <li id="toc-Intel_64" class="vector-toc-list-item vector-toc-level-1"> <a class="vector-toc-link" href="#Intel_64"> <div class="vector-toc-text"> 2 Intel 64 </div> </a> <button aria-controls="toc-Intel_64-sublist" class="cdx-button cdx-button--weight-quiet cdx-button--icon-only vector-toc-toggle"> Toggle Intel 64 subsection </button> <ul id="toc-Intel_64-sublist" class="vector-toc-list"> <li id="toc-History_2" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#History_2"> <div class="vector-toc-text"> 2.1 History </div> </a> <ul id="toc-History_2-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Implementations_2" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Implementations_2"> <div class="vector-toc-text"> 2.2 Implementations </div> </a> <ul id="toc-Implementations_2-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-X86S" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#X86S"> <div class="vector-toc-text"> 2.3 X86S </div> </a> <ul id="toc-X86S-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Advanced_Performance_Extensions" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Advanced_Performance_Extensions"> <div class="vector-toc-text"> 2.4 Advanced Performance Extensions </div> </a> <ul id="toc-Advanced_Performance_Extensions-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-VIA's_x86-64_implementation" class="vector-toc-list-item vector-toc-level-1"> <a class="vector-toc-link" href="#VIA's_x86-64_implementation"> <div class="vector-toc-text"> 3 VIA's x86-64 implementation </div> </a> <ul id="toc-VIA's_x86-64_implementation-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Microarchitecture_levels" class="vector-toc-list-item vector-toc-level-1"> <a class="vector-toc-link" href="#Microarchitecture_levels"> <div class="vector-toc-text"> 4 Microarchitecture levels </div> </a> <ul id="toc-Microarchitecture_levels-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Differences_between_AMD64_and_Intel_64" class="vector-toc-list-item vector-toc-level-1"> <a class="vector-toc-link" href="#Differences_between_AMD64_and_Intel_64"> <div class="vector-toc-text"> 5 Differences between AMD64 and Intel 64 </div> </a> <button aria-controls="toc-Differences_between_AMD64_and_Intel_64-sublist" class="cdx-button cdx-button--weight-quiet cdx-button--icon-only vector-toc-toggle"> Toggle Differences between AMD64 and Intel 64 subsection </button> <ul id="toc-Differences_between_AMD64_and_Intel_64-sublist" class="vector-toc-list"> <li id="toc-Recent_implementations" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Recent_implementations"> <div class="vector-toc-text"> 5.1 Recent implementations </div> </a> <ul id="toc-Recent_implementations-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Older_implementations" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Older_implementations"> <div class="vector-toc-text"> 5.2 Older implementations </div> </a> <ul id="toc-Older_implementations-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Adoption" class="vector-toc-list-item vector-toc-level-1"> <a class="vector-toc-link" href="#Adoption"> <div class="vector-toc-text"> 6 Adoption </div> </a> <ul id="toc-Adoption-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Operating_system_compatibility_and_characteristics" class="vector-toc-list-item vector-toc-level-1"> <a class="vector-toc-link" href="#Operating_system_compatibility_and_characteristics"> <div class="vector-toc-text"> 7 Operating system compatibility and characteristics </div> </a> <button aria-controls="toc-Operating_system_compatibility_and_characteristics-sublist" class="cdx-button cdx-button--weight-quiet cdx-button--icon-only vector-toc-toggle"> Toggle Operating system compatibility and characteristics subsection </button> <ul id="toc-Operating_system_compatibility_and_characteristics-sublist" class="vector-toc-list"> <li id="toc-BSD" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#BSD"> <div class="vector-toc-text"> 7.1 BSD </div> </a> <ul id="toc-BSD-sublist" class="vector-toc-list"> <li id="toc-DragonFly_BSD" class="vector-toc-list-item vector-toc-level-3"> <a class="vector-toc-link" href="#DragonFly_BSD"> <div class="vector-toc-text"> 7.1.1 DragonFly BSD </div> </a> <ul id="toc-DragonFly_BSD-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-FreeBSD" class="vector-toc-list-item vector-toc-level-3"> <a class="vector-toc-link" href="#FreeBSD"> <div class="vector-toc-text"> 7.1.2 FreeBSD </div> </a> <ul id="toc-FreeBSD-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-NetBSD" class="vector-toc-list-item vector-toc-level-3"> <a class="vector-toc-link" href="#NetBSD"> <div class="vector-toc-text"> 7.1.3 NetBSD </div> </a> <ul id="toc-NetBSD-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-OpenBSD" class="vector-toc-list-item vector-toc-level-3"> <a class="vector-toc-link" href="#OpenBSD"> <div class="vector-toc-text"> 7.1.4 OpenBSD </div> </a> <ul id="toc-OpenBSD-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-DOS" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#DOS"> <div class="vector-toc-text"> 7.2 DOS </div> </a> <ul id="toc-DOS-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Linux" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Linux"> <div class="vector-toc-text"> 7.3 Linux </div> </a> <ul id="toc-Linux-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-macOS" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#macOS"> <div class="vector-toc-text"> 7.4 macOS </div> </a> <ul id="toc-macOS-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Solaris" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Solaris"> <div class="vector-toc-text"> 7.5 Solaris </div> </a> <ul id="toc-Solaris-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Windows" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Windows"> <div class="vector-toc-text"> 7.6 Windows </div> </a> <ul id="toc-Windows-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Video_game_consoles" class="vector-toc-list-item vector-toc-level-1"> <a class="vector-toc-link" href="#Video_game_consoles"> <div class="vector-toc-text"> 8 Video game consoles </div> </a> <ul id="toc-Video_game_consoles-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Industry_naming_conventions" class="vector-toc-list-item vector-toc-level-1"> <a class="vector-toc-link" href="#Industry_naming_conventions"> <div class="vector-toc-text"> 9 Industry naming conventions </div> </a> <ul id="toc-Industry_naming_conventions-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Licensing" class="vector-toc-list-item vector-toc-level-1"> <a class="vector-toc-link" href="#Licensing"> <div class="vector-toc-text"> 10 Licensing </div> </a> <ul id="toc-Licensing-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-See_also" class="vector-toc-list-item vector-toc-level-1"> <a class="vector-toc-link" href="#See_also"> <div class="vector-toc-text"> 11 See also </div> </a> <ul id="toc-See_also-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Notes" class="vector-toc-list-item vector-toc-level-1"> <a class="vector-toc-link" href="#Notes"> <div class="vector-toc-text"> 12 Notes </div> </a> <ul id="toc-Notes-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-References" class="vector-toc-list-item vector-toc-level-1"> <a class="vector-toc-link" href="#References"> <div class="vector-toc-text"> 13 References </div> </a> <ul id="toc-References-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-External_links" class="vector-toc-list-item vector-toc-level-1"> <a class="vector-toc-link" href="#External_links"> <div class="vector-toc-text"> 14 External links </div> </a> <ul id="toc-External_links-sublist" class="vector-toc-list"> </ul> </li> </ul> </div> </div> </nav> </div> </div> <div class="mw-content-container"> <main id="content" class="mw-body"> <header class="mw-body-header vector-page-titlebar"> <nav aria-label="Contents" class="vector-toc-landmark"> <div id="vector-page-titlebar-toc" class="vector-dropdown vector-page-titlebar-toc vector-button-flush-left" > <input type="checkbox" id="vector-page-titlebar-toc-checkbox" role="button" aria-haspopup="true" data-event-name="ui.dropdown-vector-page-titlebar-toc" class="vector-dropdown-checkbox " aria-label="Toggle the table of contents" > <label id="vector-page-titlebar-toc-label" for="vector-page-titlebar-toc-checkbox" class="vector-dropdown-label cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet cdx-button--icon-only " aria-hidden="true" > Toggle the table of contents </label> <div class="vector-dropdown-content"> <div id="vector-page-titlebar-toc-unpinned-container" class="vector-unpinned-container"> </div> </div> </div> </nav> <h1 id="firstHeading" class="firstHeading mw-first-heading">x86-64</h1> <div id="p-lang-btn" class="vector-dropdown mw-portlet mw-portlet-lang" > <input type="checkbox" id="p-lang-btn-checkbox" role="button" aria-haspopup="true" data-event-name="ui.dropdown-p-lang-btn" class="vector-dropdown-checkbox 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Available in 35 languages" > <label id="p-lang-btn-label" for="p-lang-btn-checkbox" class="vector-dropdown-label cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet cdx-button--action-progressive mw-portlet-lang-heading-35" aria-hidden="true" > 35 languages </label> <div class="vector-dropdown-content"> <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li class="interlanguage-link interwiki-ar mw-list-item"><a href="https://ar.wikipedia.org/wiki/%D8%A5%D9%83%D8%B386-64" title="إكس86-64 – Arabic" lang="ar" hreflang="ar" data-title="إكس86-64" data-language-autonym="العربية" data-language-local-name="Arabic" class="interlanguage-link-target">العربية</a></li><li class="interlanguage-link interwiki-ca mw-list-item"><a href="https://ca.wikipedia.org/wiki/Arquitectura_x86-64" title="Arquitectura x86-64 – Catalan" lang="ca" hreflang="ca" data-title="Arquitectura x86-64" data-language-autonym="Català" data-language-local-name="Catalan" class="interlanguage-link-target">Català</a></li><li class="interlanguage-link interwiki-cs mw-list-item"><a href="https://cs.wikipedia.org/wiki/X86-64" title="X86-64 – Czech" lang="cs" hreflang="cs" data-title="X86-64" data-language-autonym="Čeština" data-language-local-name="Czech" class="interlanguage-link-target">Čeština</a></li><li class="interlanguage-link interwiki-da mw-list-item"><a href="https://da.wikipedia.org/wiki/X86-64" title="X86-64 – Danish" lang="da" hreflang="da" data-title="X86-64" data-language-autonym="Dansk" data-language-local-name="Danish" class="interlanguage-link-target">Dansk</a></li><li class="interlanguage-link interwiki-de mw-list-item"><a href="https://de.wikipedia.org/wiki/X64" title="X64 – German" lang="de" hreflang="de" data-title="X64" data-language-autonym="Deutsch" data-language-local-name="German" class="interlanguage-link-target">Deutsch</a></li><li class="interlanguage-link interwiki-et mw-list-item"><a href="https://et.wikipedia.org/wiki/X86-64" title="X86-64 – Estonian" lang="et" hreflang="et" data-title="X86-64" data-language-autonym="Eesti" data-language-local-name="Estonian" class="interlanguage-link-target">Eesti</a></li><li class="interlanguage-link interwiki-el mw-list-item"><a href="https://el.wikipedia.org/wiki/X86-64" title="X86-64 – Greek" lang="el" hreflang="el" data-title="X86-64" data-language-autonym="Ελληνικά" data-language-local-name="Greek" class="interlanguage-link-target">Ελληνικά</a></li><li class="interlanguage-link interwiki-es mw-list-item"><a href="https://es.wikipedia.org/wiki/X86-64" title="X86-64 – Spanish" lang="es" hreflang="es" data-title="X86-64" data-language-autonym="Español" data-language-local-name="Spanish" class="interlanguage-link-target">Español</a></li><li class="interlanguage-link interwiki-fa mw-list-item"><a href="https://fa.wikipedia.org/wiki/X86-64" title="X86-64 – Persian" lang="fa" hreflang="fa" data-title="X86-64" data-language-autonym="فارسی" data-language-local-name="Persian" class="interlanguage-link-target">فارسی</a></li><li class="interlanguage-link interwiki-fr mw-list-item"><a href="https://fr.wikipedia.org/wiki/X64" title="X64 – French" lang="fr" hreflang="fr" data-title="X64" data-language-autonym="Français" data-language-local-name="French" class="interlanguage-link-target">Français</a></li><li class="interlanguage-link interwiki-ko mw-list-item"><a href="https://ko.wikipedia.org/wiki/X86-64" title="X86-64 – Korean" lang="ko" hreflang="ko" data-title="X86-64" data-language-autonym="한국어" data-language-local-name="Korean" class="interlanguage-link-target">한국어</a></li><li class="interlanguage-link interwiki-hi mw-list-item"><a href="https://hi.wikipedia.org/wiki/X%E0%A5%AE%E0%A5%AC-%E0%A5%AC%E0%A5%AA" title="X८६-६४ – Hindi" lang="hi" hreflang="hi" data-title="X८६-६४" data-language-autonym="हिन्दी" data-language-local-name="Hindi" class="interlanguage-link-target">हिन्दी</a></li><li class="interlanguage-link interwiki-it mw-list-item"><a href="https://it.wikipedia.org/wiki/X86-64" title="X86-64 – Italian" lang="it" hreflang="it" data-title="X86-64" data-language-autonym="Italiano" data-language-local-name="Italian" class="interlanguage-link-target">Italiano</a></li><li class="interlanguage-link interwiki-he mw-list-item"><a href="https://he.wikipedia.org/wiki/X86-64" title="X86-64 – Hebrew" lang="he" hreflang="he" data-title="X86-64" data-language-autonym="עברית" data-language-local-name="Hebrew" class="interlanguage-link-target">עברית</a></li><li class="interlanguage-link interwiki-hu mw-list-item"><a href="https://hu.wikipedia.org/wiki/X86-64" title="X86-64 – Hungarian" lang="hu" hreflang="hu" data-title="X86-64" data-language-autonym="Magyar" data-language-local-name="Hungarian" class="interlanguage-link-target">Magyar</a></li><li class="interlanguage-link interwiki-ml mw-list-item"><a href="https://ml.wikipedia.org/wiki/%E0%B4%8E%E0%B4%8E%E0%B4%82%E0%B4%A1%E0%B4%BF64(X86-64)" title="എഎംഡി64(X86-64) – Malayalam" lang="ml" hreflang="ml" data-title="എഎംഡി64(X86-64)" data-language-autonym="മലയാളം" data-language-local-name="Malayalam" class="interlanguage-link-target">മലയാളം</a></li><li class="interlanguage-link interwiki-ms mw-list-item"><a href="https://ms.wikipedia.org/wiki/X86-64" title="X86-64 – Malay" lang="ms" hreflang="ms" data-title="X86-64" data-language-autonym="Bahasa Melayu" data-language-local-name="Malay" class="interlanguage-link-target">Bahasa Melayu</a></li><li class="interlanguage-link interwiki-nl mw-list-item"><a href="https://nl.wikipedia.org/wiki/X86-64" title="X86-64 – Dutch" lang="nl" hreflang="nl" data-title="X86-64" data-language-autonym="Nederlands" data-language-local-name="Dutch" class="interlanguage-link-target">Nederlands</a></li><li class="interlanguage-link interwiki-ja mw-list-item"><a href="https://ja.wikipedia.org/wiki/X64" title="X64 – Japanese" lang="ja" hreflang="ja" data-title="X64" data-language-autonym="日本語" data-language-local-name="Japanese" class="interlanguage-link-target">日本語</a></li><li class="interlanguage-link interwiki-no mw-list-item"><a href="https://no.wikipedia.org/wiki/X86-64" title="X86-64 – Norwegian Bokmål" lang="nb" hreflang="nb" data-title="X86-64" data-language-autonym="Norsk bokmål" data-language-local-name="Norwegian Bokmål" class="interlanguage-link-target">Norsk bokmål</a></li><li class="interlanguage-link interwiki-pl mw-list-item"><a href="https://pl.wikipedia.org/wiki/X86-64" title="X86-64 – Polish" lang="pl" hreflang="pl" data-title="X86-64" data-language-autonym="Polski" data-language-local-name="Polish" class="interlanguage-link-target">Polski</a></li><li class="interlanguage-link interwiki-ro mw-list-item"><a href="https://ro.wikipedia.org/wiki/X86-64" title="X86-64 – Romanian" lang="ro" hreflang="ro" data-title="X86-64" data-language-autonym="Română" data-language-local-name="Romanian" class="interlanguage-link-target">Română</a></li><li class="interlanguage-link interwiki-qu mw-list-item"><a href="https://qu.wikipedia.org/wiki/X86-64" title="X86-64 – Quechua" lang="qu" hreflang="qu" data-title="X86-64" data-language-autonym="Runa Simi" data-language-local-name="Quechua" class="interlanguage-link-target">Runa Simi</a></li><li class="interlanguage-link interwiki-ru mw-list-item"><a href="https://ru.wikipedia.org/wiki/X86-64" title="X86-64 – Russian" lang="ru" hreflang="ru" data-title="X86-64" data-language-autonym="Русский" data-language-local-name="Russian" class="interlanguage-link-target">Русский</a></li><li class="interlanguage-link interwiki-simple mw-list-item"><a href="https://simple.wikipedia.org/wiki/X64" title="X64 – Simple English" lang="en-simple" hreflang="en-simple" data-title="X64" data-language-autonym="Simple English" data-language-local-name="Simple English" class="interlanguage-link-target">Simple English</a></li><li class="interlanguage-link interwiki-sk mw-list-item"><a href="https://sk.wikipedia.org/wiki/X86-64" title="X86-64 – Slovak" lang="sk" hreflang="sk" data-title="X86-64" data-language-autonym="Slovenčina" data-language-local-name="Slovak" class="interlanguage-link-target">Slovenčina</a></li><li class="interlanguage-link interwiki-sl mw-list-item"><a href="https://sl.wikipedia.org/wiki/X86-64" title="X86-64 – Slovenian" lang="sl" hreflang="sl" data-title="X86-64" data-language-autonym="Slovenščina" data-language-local-name="Slovenian" class="interlanguage-link-target">Slovenščina</a></li><li class="interlanguage-link interwiki-sr mw-list-item"><a href="https://sr.wikipedia.org/wiki/X86-64" title="X86-64 – Serbian" lang="sr" hreflang="sr" data-title="X86-64" data-language-autonym="Српски / srpski" data-language-local-name="Serbian" class="interlanguage-link-target">Српски / srpski</a></li><li class="interlanguage-link interwiki-sv mw-list-item"><a href="https://sv.wikipedia.org/wiki/AMD64" title="AMD64 – Swedish" lang="sv" hreflang="sv" data-title="AMD64" data-language-autonym="Svenska" data-language-local-name="Swedish" class="interlanguage-link-target">Svenska</a></li><li class="interlanguage-link interwiki-th mw-list-item"><a href="https://th.wikipedia.org/wiki/%E0%B9%80%E0%B8%AD%E0%B8%81%E0%B8%8B%E0%B9%8C86-64" title="เอกซ์86-64 – Thai" lang="th" hreflang="th" data-title="เอกซ์86-64" data-language-autonym="ไทย" data-language-local-name="Thai" class="interlanguage-link-target">ไทย</a></li><li class="interlanguage-link interwiki-tr mw-list-item"><a href="https://tr.wikipedia.org/wiki/X86-64" title="X86-64 – Turkish" lang="tr" hreflang="tr" data-title="X86-64" data-language-autonym="Türkçe" data-language-local-name="Turkish" class="interlanguage-link-target">Türkçe</a></li><li class="interlanguage-link interwiki-uk mw-list-item"><a href="https://uk.wikipedia.org/wiki/X86-64" title="X86-64 – Ukrainian" lang="uk" hreflang="uk" 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data-mw-ve-target-container> <div class="vector-body-before-content"> <div class="mw-indicators"> </div> <div id="siteSub" class="noprint">From Wikipedia, the free encyclopedia</div> </div> <div id="contentSub"><div id="mw-content-subtitle">(Redirected from <a href="/w/index.php?title=X64&redirect=no" class="mw-redirect" title="X64">X64</a>)</div></div> <div id="mw-content-text" class="mw-body-content"><div class="mw-content-ltr mw-parser-output" lang="en" dir="ltr"><div class="shortdescription nomobile noexcerpt noprint searchaux" style="display:none">64-bit version of x86 architecture</div> <style data-mw-deduplicate="TemplateStyles:r1236090951">.mw-parser-output .hatnote{font-style:italic}.mw-parser-output div.hatnote{padding-left:1.6em;margin-bottom:0.5em}.mw-parser-output .hatnote i{font-style:normal}.mw-parser-output .hatnote+link+.hatnote{margin-top:-0.5em}@media print{body.ns-0 .mw-parser-output .hatnote{display:none!important}}</style><div role="note" class="hatnote navigation-not-searchable">"Intel 64" redirects here. For the Intel 64-bit architecture in Itanium chips, see <a href="/wiki/IA-64" title="IA-64">IA-64</a>.</div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">"x64" redirects here. For the New York City bus route, see <a href="/wiki/X64_(New_York_City_bus)" class="mw-redirect" title="X64 (New York City bus)">X64 (New York City bus)</a>.</div> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:AMD_Opteron_146_Venus,_2005.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/6/67/AMD_Opteron_146_Venus%2C_2005.jpg/220px-AMD_Opteron_146_Venus%2C_2005.jpg" decoding="async" width="220" height="221" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/6/67/AMD_Opteron_146_Venus%2C_2005.jpg/330px-AMD_Opteron_146_Venus%2C_2005.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/6/67/AMD_Opteron_146_Venus%2C_2005.jpg/440px-AMD_Opteron_146_Venus%2C_2005.jpg 2x" data-file-width="1003" data-file-height="1008" /></a><figcaption><a href="/wiki/AMD" title="AMD">AMD</a> <a href="/wiki/Opteron" title="Opteron">Opteron</a>, the first CPU to introduce the x86-64 extensions in April 2003</figcaption></figure> <figure class="mw-default-size mw-halign-right" typeof="mw:File/Thumb"><a href="/wiki/File:AMD_x86-64_Architecture_Programmers_Manuals.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/3/30/AMD_x86-64_Architecture_Programmers_Manuals.jpg/220px-AMD_x86-64_Architecture_Programmers_Manuals.jpg" decoding="async" width="220" height="155" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/3/30/AMD_x86-64_Architecture_Programmers_Manuals.jpg/330px-AMD_x86-64_Architecture_Programmers_Manuals.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/3/30/AMD_x86-64_Architecture_Programmers_Manuals.jpg/440px-AMD_x86-64_Architecture_Programmers_Manuals.jpg 2x" data-file-width="768" data-file-height="540" /></a><figcaption>The five-volume set of the x86-64 Architecture Programmer's Manual, as published and distributed by AMD in 2002</figcaption></figure> x86-64 (also known as x64, x86_64, AMD64, and Intel 64)<a href="#cite_note-11">[note 1]</a> is a <a href="/wiki/64-bit" class="mw-redirect" title="64-bit">64-bit</a> version of the <a href="/wiki/X86" title="X86">x86</a> <a href="/wiki/Instruction_set" class="mw-redirect" title="Instruction set">instruction set</a>, first announced in 1999. It introduced two new modes of operation, 64-bit mode and compatibility mode, along with a new 4-level <a href="/wiki/Paging" class="mw-redirect" title="Paging">paging</a> mode. With 64-bit mode and the new paging mode, it supports vastly larger amounts of <a href="/wiki/Virtual_memory" title="Virtual memory">virtual memory</a> and <a href="/wiki/Physical_memory" class="mw-redirect" title="Physical memory">physical memory</a> than was possible on its <a href="/wiki/32-bit_computing" title="32-bit computing">32-bit</a> predecessors, allowing programs to store larger amounts of data in memory. x86-64 also expands <a href="/wiki/General-purpose_register" class="mw-redirect" title="General-purpose register">general-purpose registers</a> to 64-bit, and expands the number of them from 8 (some of which had limited or fixed functionality, e.g. for stack management) to 16 (fully general), and provides numerous other enhancements. <a href="/wiki/Floating-point_arithmetic" title="Floating-point arithmetic">Floating-point arithmetic</a> is supported via mandatory <a href="/wiki/SSE2" title="SSE2">SSE2</a>-like instructions[<a href="/wiki/Wikipedia:Citation_needed" title="Wikipedia:Citation needed"><span title="The AMD64 Architecture’s Programmers Manual Volume 1 pg 276f recommends that the programmer checks for SSE2 support, The Xeon Phi claims that it only supports AVX/AVX2/AVX512 and not SSE (August 2024)">citation needed</a>], and <a href="/wiki/X87" title="X87">x87</a>/<a href="/wiki/MMX_(instruction_set)" title="MMX (instruction set)">MMX</a> style registers are generally not used (but still available even in 64-bit mode); instead, a set of 16 <a href="/wiki/Vector_registers" class="mw-redirect" title="Vector registers">vector registers</a>, 128 bits each, is used. (Each register can store one or two <a href="/wiki/Double-precision_floating-point_format" title="Double-precision floating-point format">double-precision</a> numbers or one to four <a href="/wiki/Single-precision_floating-point_format" title="Single-precision floating-point format">single-precision</a> numbers, or various integer formats.) In 64-bit mode, instructions are modified to support 64-bit <a href="/wiki/Operands" class="mw-redirect" title="Operands">operands</a> and 64-bit <a href="/wiki/Addressing_mode" title="Addressing mode">addressing mode</a>. The compatibility mode defined in the architecture allows 16-bit and 32-bit <a href="/wiki/User_space" class="mw-redirect" title="User space">user applications</a> to run unmodified, coexisting with 64-bit applications if the 64-bit operating system supports them.<a href="#cite_note-amd-24593-12">[11]</a><a href="#cite_note-14">[note 2]</a> As the full x86 16-bit and 32-bit instruction sets remain implemented in hardware without any intervening emulation, these older <a href="/wiki/Executable" title="Executable">executables</a> can run with little or no performance penalty,<a href="#cite_note-x86-compat-perf-15">[13]</a> while newer or modified applications can take advantage of new features of the processor design to achieve performance improvements. Also, a processor supporting x86-64 still powers on in <a href="/wiki/Real_mode" title="Real mode">real mode</a> for full <a href="/wiki/Backward_compatibility" title="Backward compatibility">backward compatibility</a> with the <a href="/wiki/Intel_8086" title="Intel 8086">8086</a>, as x86 processors supporting <a href="/wiki/Protected_mode" title="Protected mode">protected mode</a> have done since the <a href="/wiki/Intel_80286" title="Intel 80286">80286</a>. The original specification, created by <a href="/wiki/AMD" title="AMD">AMD</a> and released in 2000, has been implemented by AMD, <a href="/wiki/Intel_Corporation" class="mw-redirect" title="Intel Corporation">Intel</a>, and <a href="/wiki/VIA_Technologies" title="VIA Technologies">VIA</a>. The <a href="/wiki/AMD_K8" title="AMD K8">AMD K8</a> <a href="/wiki/Microarchitecture" title="Microarchitecture">microarchitecture</a>, in the <a href="/wiki/Opteron" title="Opteron">Opteron</a> and <a href="/wiki/Athlon_64" title="Athlon 64">Athlon 64</a> processors, was the first to implement it. This was the first significant addition to the <a href="/wiki/X86" title="X86">x86</a> architecture designed by a company other than Intel. Intel was forced to follow suit and introduced a modified <a href="/wiki/NetBurst" title="NetBurst">NetBurst</a> family which was software-compatible with AMD's specification. <a href="/wiki/VIA_Technologies" title="VIA Technologies">VIA Technologies</a> introduced x86-64 in their VIA Isaiah architecture, with the <a href="/wiki/VIA_Nano" title="VIA Nano">VIA Nano</a>. The x86-64 architecture was quickly adopted for desktop and laptop personal computers and servers which were commonly configured for 16 GiB (<a href="/wiki/Gibibyte" class="mw-redirect" title="Gibibyte">gibibytes</a>) of memory or more. It has effectively replaced the discontinued Intel <a href="/wiki/Itanium" title="Itanium">Itanium</a> architecture (formerly <a href="/wiki/IA-64" title="IA-64">IA-64</a>), which was originally intended to replace the x86 architecture. x86-64 and Itanium are not compatible on the native instruction set level, and operating systems and applications compiled for one architecture cannot be run on the other natively. <meta property="mw:PageProp/toc" /> <div class="mw-heading mw-heading2"><h2 id="AMD64">AMD64</h2>[<a href="/w/index.php?title=X86-64&action=edit&section=1" title="Edit section: AMD64">edit</a>]</div> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:AMD64_Logo.svg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/1/1a/AMD64_Logo.svg/110px-AMD64_Logo.svg.png" decoding="async" width="110" height="110" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/1/1a/AMD64_Logo.svg/165px-AMD64_Logo.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/1/1a/AMD64_Logo.svg/220px-AMD64_Logo.svg.png 2x" data-file-width="144" data-file-height="144" /></a><figcaption>AMD64 logo</figcaption></figure> <div class="mw-heading mw-heading3"><h3 id="History">History</h3>[<a href="/w/index.php?title=X86-64&action=edit&section=2" title="Edit section: History">edit</a>]</div> AMD64 (also variously referred to by <a href="/wiki/AMD" title="AMD">AMD</a> in their literature and documentation as “AMD 64-bit Technology” and “AMD x86-64 Architecture”) was created as an alternative to the radically different <a href="/wiki/IA-64" title="IA-64">IA-64</a> architecture designed by <a href="/wiki/Intel" title="Intel">Intel</a> and <a href="/wiki/Hewlett-Packard" title="Hewlett-Packard">Hewlett-Packard</a>, which was <a href="/wiki/Backward_compatibility" title="Backward compatibility">backward-incompatible</a> with <a href="/wiki/IA-32" title="IA-32">IA-32</a>, the 32-bit version of the <a href="/wiki/X86" title="X86">x86</a> architecture. AMD originally announced AMD64 in 1999<a href="#cite_note-16">[14]</a> with a full specification available in August 2000.<a href="#cite_note-17">[15]</a> As AMD was never invited to be a contributing party for the IA-64 architecture and any kind of licensing seemed unlikely, the AMD64 architecture was positioned by AMD from the beginning as an evolutionary way to add <a href="/wiki/64-bit_computing" title="64-bit computing">64-bit computing</a> capabilities to the existing x86 architecture while supporting legacy 32-bit x86 <a href="/wiki/Machine_code" title="Machine code">code</a>, as opposed to Intel's approach of creating an entirely new, completely x86-incompatible 64-bit architecture with IA-64. The first AMD64-based processor, the <a href="/wiki/Opteron" title="Opteron">Opteron</a>, was released in April 2003. <div class="mw-heading mw-heading3"><h3 id="Implementations">Implementations</h3>[<a href="/w/index.php?title=X86-64&action=edit&section=3" title="Edit section: Implementations">edit</a>]</div> AMD's processors implementing the AMD64 architecture include <a href="/wiki/Opteron" title="Opteron">Opteron</a>, <a href="/wiki/Athlon_64" title="Athlon 64">Athlon 64</a>, <a href="/wiki/Athlon_64_X2" title="Athlon 64 X2">Athlon 64 X2</a>, <a href="/wiki/Athlon_64_FX" class="mw-redirect" title="Athlon 64 FX">Athlon 64 FX</a>, <a href="/wiki/Athlon_II" title="Athlon II">Athlon II</a> (followed by "X2", "X3", or "X4" to indicate the number of cores, and XLT models), <a href="/wiki/Turion_64" class="mw-redirect" title="Turion 64">Turion 64</a>, <a href="/wiki/Turion_64_X2" class="mw-redirect" title="Turion 64 X2">Turion 64 X2</a>, <a href="/wiki/Sempron" title="Sempron">Sempron</a> ("Palermo" E6 stepping and all "Manila" models), <a href="/wiki/Phenom_(processor)" class="mw-redirect" title="Phenom (processor)">Phenom</a> (followed by "X3" or "X4" to indicate the number of cores), <a href="/wiki/Phenom_II" title="Phenom II">Phenom II</a> (followed by "X2", "X3", "X4" or "X6" to indicate the number of cores), <a href="/wiki/AMD_FX" title="AMD FX">FX</a>, <a href="/wiki/AMD_Accelerated_Processing_Unit" class="mw-redirect" title="AMD Accelerated Processing Unit">Fusion/APU</a> and <a href="/wiki/Ryzen" title="Ryzen">Ryzen</a>/<a href="/wiki/Epyc" title="Epyc">Epyc</a>. <div class="mw-heading mw-heading3"><h3 id="Architectural_features">Architectural features</h3>[<a href="/w/index.php?title=X86-64&action=edit&section=4" title="Edit section: Architectural features">edit</a>]</div> The primary defining characteristic of AMD64 is the availability of 64-bit general-purpose <a href="/wiki/Processor_register" title="Processor register">processor registers</a> (for example, <style data-mw-deduplicate="TemplateStyles:r886049734">.mw-parser-output .monospaced{font-family:monospace,monospace}</style>rax), 64-bit <a href="/wiki/Integer_(computer_science)" title="Integer (computer science)">integer</a> arithmetic and logical operations, and 64-bit <a href="/wiki/Protected_Virtual_Address_Mode" class="mw-redirect" title="Protected Virtual Address Mode">virtual addresses</a>.<a href="#cite_note-18">[16]</a> The designers took the opportunity to make other improvements as well. Notable changes in the 64-bit extensions include: <dl><dt>64-bit integer capability</dt> <dd>All <a href="/wiki/General-purpose_register" class="mw-redirect" title="General-purpose register">general-purpose registers</a> (GPRs) are expanded from 32 <a href="/wiki/Bit" title="Bit">bits</a> to 64 bits, and all arithmetic and logical operations, memory-to-register and register-to-memory operations, etc., can operate directly on 64-bit integers. <a href="/wiki/Stack_(data_structure)" class="mw-redirect" title="Stack (data structure)">Pushes and pops</a> on the <a href="/wiki/Stack_register" title="Stack register">stack</a> default to 8-byte strides, and <a href="/wiki/Pointer_(computer_programming)" title="Pointer (computer programming)">pointers</a> are 8 bytes wide.</dd> <dt>Additional registers</dt> <dd>In addition to increasing the size of the general-purpose registers, the number of named general-purpose registers is increased from eight (i.e. <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r886049734">eax, <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r886049734">ecx, <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r886049734">edx, <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r886049734">ebx, <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r886049734">esp, <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r886049734">ebp, <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r886049734">esi, <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r886049734">edi) in x86 to 16 (i.e. <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r886049734">rax, <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r886049734">rcx, <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r886049734">rdx, <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r886049734">rbx, <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r886049734">rsp, <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r886049734">rbp, <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r886049734">rsi, <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r886049734">rdi, <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r886049734">r8, <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r886049734">r9, <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r886049734">r10, <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r886049734">r11, <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r886049734">r12, <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r886049734">r13, <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r886049734">r14, <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r886049734">r15). It is therefore possible to keep more local variables in registers rather than on the stack, and to let registers hold frequently accessed constants; arguments for small and fast subroutines may also be passed in registers to a greater extent.</dd> <dd>AMD64 still has fewer registers than many <a href="/wiki/RISC" class="mw-redirect" title="RISC">RISC</a> <a href="/wiki/Instruction_set" class="mw-redirect" title="Instruction set">instruction sets</a> (e.g. <a href="/wiki/Power_ISA" title="Power ISA">Power ISA</a> has 32 GPRs; <a href="/wiki/ARM_architecture#64/32-bit_architecture" class="mw-redirect" title="ARM architecture">64-bit ARM</a>, <a href="/wiki/RISC-V" title="RISC-V">RISC-V</a> I, <a href="/wiki/SPARC" title="SPARC">SPARC</a>, <a href="/wiki/DEC_Alpha" title="DEC Alpha">Alpha</a>, <a href="/wiki/MIPS_architecture" title="MIPS architecture">MIPS</a>, and <a href="/wiki/PA-RISC" title="PA-RISC">PA-RISC</a> have 31) or <a href="/wiki/VLIW" class="mw-redirect" title="VLIW">VLIW</a>-like machines such as the <a href="/wiki/IA-64" title="IA-64">IA-64</a> (which has 128 registers). However, an AMD64 implementation may have far more internal registers than the number of architectural registers exposed by the instruction set (see <a href="/wiki/Register_renaming" title="Register renaming">register renaming</a>). (For example, AMD Zen cores have 168 64-bit integer and 160 128-bit vector floating-point physical internal registers.)</dd> <dt>Additional XMM (SSE) registers</dt> <dd>Similarly, the number of 128-bit XMM registers (used for <a href="/wiki/Streaming_SIMD_Extensions" title="Streaming SIMD Extensions">Streaming SIMD</a> instructions) is also increased from 8 to 16.</dd> <dd>The traditional x87 FPU register stack is not included in the register file size extension in 64-bit mode, compared with the XMM registers used by SSE2, which did get extended. The <a href="/wiki/X87" title="X87">x87</a> register stack is not a simple register file although it does allow direct access to individual registers by low cost exchange operations.</dd> <dt>Larger virtual address space</dt> <dd>The AMD64 architecture defines a 64-bit virtual address format, of which the low-order 48 bits are used in current implementations.<a href="#cite_note-amd-24593-12">[11]</a>: 120  This allows up to 256 <a href="/wiki/Tebibyte" class="mw-redirect" title="Tebibyte">TiB</a> (248 <a href="/wiki/Byte" title="Byte">bytes</a>) of virtual address space. The architecture definition allows this limit to be raised in future implementations to the full 64 bits,<a href="#cite_note-amd-24593-12">[11]</a>: 2 : 3 : 13 : 117 : 120  extending the virtual address space to 16 <a href="/wiki/Exbibyte" class="mw-redirect" title="Exbibyte">EiB</a> (264 bytes).<a href="#cite_note-19">[17]</a> This is compared to just 4 <a href="/wiki/Gibibyte" class="mw-redirect" title="Gibibyte">GiB</a> (232 bytes) for the x86.<a href="#cite_note-intel-253668-20">[18]</a></dd> <dd>This means that very large files can be operated on by <a href="/wiki/Memory-mapped_file" title="Memory-mapped file">mapping</a> the entire file into the process's address space (which is often much faster than working with file read/write calls), rather than having to map regions of the file into and out of the address space.</dd> <dt>Larger physical address space</dt> <dd>The original implementation of the AMD64 architecture implemented 40-bit <a href="/wiki/Physical_address" title="Physical address">physical addresses</a> and so could address up to 1 TiB (240 bytes) of RAM.<a href="#cite_note-amd-24593-12">[11]</a>: 24  Current implementations of the AMD64 architecture (starting from <a href="/wiki/AMD_K10" class="mw-redirect" title="AMD K10">AMD 10h microarchitecture</a>) extend this to 48-bit physical addresses<a href="#cite_note-amd10h-21">[19]</a> and therefore can address up to 256 TiB (248 bytes) of RAM. The architecture permits extending this to 52 bits in the future<a href="#cite_note-amd-24593-12">[11]</a>: 24 <a href="#cite_note-22">[20]</a> (limited by the page table entry format);<a href="#cite_note-amd-24593-12">[11]</a>: 131  this would allow addressing of up to 4 PiB of RAM. For comparison, 32-bit x86 processors are limited to 64 GiB of RAM in <a href="/wiki/Physical_Address_Extension" title="Physical Address Extension">Physical Address Extension</a> (PAE) mode,<a href="#cite_note-shanley-ppro-23">[21]</a> or 4 GiB of RAM without PAE mode.<a href="#cite_note-amd-24593-12">[11]</a>: 4 </dd> <dt>Larger physical address space in legacy mode</dt> <dd>When operating in <a href="/wiki/Legacy_mode" title="Legacy mode">legacy mode</a> the AMD64 architecture supports <a href="/wiki/Physical_Address_Extension" title="Physical Address Extension">Physical Address Extension</a> (PAE) mode, as do most current x86 processors, but AMD64 extends PAE from 36 bits to an architectural limit of 52 bits of physical address. Any implementation, therefore, allows the same physical address limit as under <a href="/wiki/Long_mode" title="Long mode">long mode</a>.<a href="#cite_note-amd-24593-12">[11]</a>: 24 </dd> <dt>Instruction pointer relative data access</dt> <dd>Instructions can now reference data relative to the instruction pointer (RIP register). This makes <a href="/wiki/Position-independent_code" title="Position-independent code">position-independent code</a>, as is often used in <a href="/wiki/Library_(computing)#Shared_libraries" title="Library (computing)">shared libraries</a> and code loaded at run time, more efficient.</dd> <dt>SSE instructions</dt> <dd>The original AMD64 architecture adopted Intel's <a href="/wiki/Streaming_SIMD_Extensions" title="Streaming SIMD Extensions">SSE</a> and <a href="/wiki/SSE2" title="SSE2">SSE2</a> as core instructions. These instruction sets provide a vector supplement to the scalar <a href="/wiki/X87" title="X87">x87</a> FPU, for the single-precision and double-precision data types. SSE2 also offers integer vector operations, for data types ranging from 8bit to 64bit precision. This makes the vector capabilities of the architecture on par with those of the most advanced x86 processors of its time. These instructions can also be used in 32-bit mode. The proliferation of 64-bit processors has made these vector capabilities ubiquitous in home computers, allowing the improvement of the standards of 32-bit applications. The 32-bit edition of Windows 8, for example, requires the presence of SSE2 instructions.<a href="#cite_note-24">[22]</a> <a href="/wiki/SSE3" title="SSE3">SSE3</a> instructions and later <a href="/wiki/Streaming_SIMD_Extensions" title="Streaming SIMD Extensions">Streaming SIMD Extensions</a> instruction sets are not standard features of the architecture.</dd> <dt>No-Execute bit</dt> <dd>The No-Execute bit or <a href="/wiki/NX_bit" title="NX bit">NX bit</a> (bit 63 of the page table entry) allows the operating system to specify which pages of virtual address space can contain executable code and which cannot. An attempt to execute code from a page tagged "no execute" will result in a memory access violation, similar to an attempt to write to a read-only page. This should make it more difficult for malicious code to take control of the system via "<a href="/wiki/Buffer_overflow" title="Buffer overflow">buffer overrun</a>" or "unchecked buffer" attacks. A similar feature has been available on x86 processors since the <a href="/wiki/80286" class="mw-redirect" title="80286">80286</a> as an attribute of <a href="/wiki/Segment_descriptor" title="Segment descriptor">segment descriptors</a>; however, this works only on an entire segment at a time.</dd> <dd><a href="/wiki/X86_memory_segmentation" title="X86 memory segmentation">Segmented addressing</a> has long been considered an obsolete mode of operation, and all current PC operating systems in effect bypass it, setting all segments to a base address of zero and (in their 32-bit implementation) a size of 4 GiB. AMD was the first x86-family vendor to implement no-execute in linear addressing mode. The feature is also available in legacy mode on AMD64 processors, and recent Intel x86 processors, when PAE is used.</dd> <dt>Removal of older features</dt> <dd>A few "system programming" features of the x86 architecture were either unused or underused in modern operating systems and are either not available on AMD64 in long (64-bit and compatibility) mode, or exist only in limited form. These include segmented addressing (although the FS and GS segments are retained in vestigial form for use as extra-base pointers to operating system structures),<a href="#cite_note-amd-24593-12">[11]</a>: 70  the <a href="/wiki/Task_State_Segment" class="mw-redirect" title="Task State Segment">task state switch</a> mechanism, and <a href="/wiki/Virtual_8086_mode" title="Virtual 8086 mode">virtual 8086 mode</a>. These features remain fully implemented in "legacy mode", allowing these processors to run 32-bit and 16-bit operating systems without modifications. Some instructions that proved to be rarely useful are not supported in 64-bit mode, including saving/restoring of segment registers on the stack, saving/restoring of all registers (PUSHA/POPA), decimal arithmetic, BOUND and INTO instructions, and "far" jumps and calls with immediate operands.</dd></dl> <div class="mw-heading mw-heading3"><h3 id="Virtual_address_space_details">Virtual address space details</h3>[<a href="/w/index.php?title=X86-64&action=edit&section=5" title="Edit section: Virtual address space details">edit</a>]</div> <div class="mw-heading mw-heading4"><h4 id="Canonical_form_addresses">Canonical form addresses</h4>[<a href="/w/index.php?title=X86-64&action=edit&section=6" title="Edit section: Canonical form addresses">edit</a>]</div> <style data-mw-deduplicate="TemplateStyles:r1237032888/mw-parser-output/.tmulti">.mw-parser-output .tmulti .multiimageinner{display:flex;flex-direction:column}.mw-parser-output .tmulti .trow{display:flex;flex-direction:row;clear:left;flex-wrap:wrap;width:100%;box-sizing:border-box}.mw-parser-output .tmulti .tsingle{margin:1px;float:left}.mw-parser-output .tmulti .theader{clear:both;font-weight:bold;text-align:center;align-self:center;background-color:transparent;width:100%}.mw-parser-output .tmulti .thumbcaption{background-color:transparent}.mw-parser-output .tmulti .text-align-left{text-align:left}.mw-parser-output .tmulti .text-align-right{text-align:right}.mw-parser-output .tmulti .text-align-center{text-align:center}@media all and (max-width:720px){.mw-parser-output .tmulti .thumbinner{width:100%!important;box-sizing:border-box;max-width:none!important;align-items:center}.mw-parser-output .tmulti .trow{justify-content:center}.mw-parser-output .tmulti .tsingle{float:none!important;max-width:100%!important;box-sizing:border-box;text-align:center}.mw-parser-output .tmulti .tsingle .thumbcaption{text-align:left}.mw-parser-output .tmulti .trow>.thumbcaption{text-align:center}}@media screen{html.skin-theme-clientpref-night .mw-parser-output .tmulti .multiimageinner img{background-color:white}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .tmulti .multiimageinner img{background-color:white}}</style><div class="thumb tmulti tright"><div class="thumbinner multiimageinner" style="width:462px;max-width:462px"><div class="trow"><div class="theader">Canonical address space implementations (diagrams not to scale)</div></div><div class="trow"><div class="tsingle" style="width:152px;max-width:152px"><div class="thumbimage"><a href="/wiki/File:AMD64-canonical--48-bit.svg" class="mw-file-description"><img alt="" src="//upload.wikimedia.org/wikipedia/commons/thumb/2/2a/AMD64-canonical--48-bit.svg/150px-AMD64-canonical--48-bit.svg.png" decoding="async" width="150" height="263" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/2/2a/AMD64-canonical--48-bit.svg/225px-AMD64-canonical--48-bit.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/2/2a/AMD64-canonical--48-bit.svg/300px-AMD64-canonical--48-bit.svg.png 2x" data-file-width="200" data-file-height="350" /></a></div><div class="thumbcaption">Current 48-bit implementation</div></div><div class="tsingle" style="width:152px;max-width:152px"><div class="thumbimage"><a href="/wiki/File:AMD64-canonical--57-bit.svg" class="mw-file-description"><img alt="" src="//upload.wikimedia.org/wikipedia/commons/thumb/b/be/AMD64-canonical--57-bit.svg/150px-AMD64-canonical--57-bit.svg.png" decoding="async" width="150" height="263" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/b/be/AMD64-canonical--57-bit.svg/225px-AMD64-canonical--57-bit.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/b/be/AMD64-canonical--57-bit.svg/300px-AMD64-canonical--57-bit.svg.png 2x" data-file-width="200" data-file-height="350" /></a></div><div class="thumbcaption">57-bit implementation</div></div><div class="tsingle" style="width:152px;max-width:152px"><div class="thumbimage"><a href="/wiki/File:AMD64-canonical--64-bit.svg" class="mw-file-description"><img alt="" src="//upload.wikimedia.org/wikipedia/commons/thumb/4/45/AMD64-canonical--64-bit.svg/150px-AMD64-canonical--64-bit.svg.png" decoding="async" width="150" height="263" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/4/45/AMD64-canonical--64-bit.svg/225px-AMD64-canonical--64-bit.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/4/45/AMD64-canonical--64-bit.svg/300px-AMD64-canonical--64-bit.svg.png 2x" data-file-width="200" data-file-height="350" /></a></div><div class="thumbcaption">64-bit implementation</div></div></div></div></div> Although virtual addresses are 64 bits wide in 64-bit mode, current implementations (and all chips that are known to be in the planning stages) do not allow the entire virtual address space of 264 bytes (16 <a href="/wiki/Exbibyte" class="mw-redirect" title="Exbibyte">EiB</a>) to be used. This would be approximately four billion times the size of the virtual address space on 32-bit machines. Most operating systems and applications will not need such a large address space for the foreseeable future, so implementing such wide virtual addresses would simply increase the complexity and cost of address translation with no real benefit. AMD, therefore, decided that, in the first implementations of the architecture, only the least significant 48 bits of a virtual address would actually be used in address translation (<a href="/wiki/Page_table" title="Page table">page table</a> lookup).<a href="#cite_note-amd-24593-12">[11]</a>: 120  In addition, the AMD specification requires that the most significant 16 bits of any virtual address, bits 48 through 63, must be copies of bit 47 (in a manner akin to <a href="/wiki/Sign_extension" title="Sign extension">sign extension</a>). If this requirement is not met, the processor will raise an exception.<a href="#cite_note-amd-24593-12">[11]</a>: 131  Addresses complying with this rule are referred to as "canonical form."<a href="#cite_note-amd-24593-12">[11]</a>: 130  Canonical form addresses run from 0 through 00007FFF'FFFFFFFF, and from FFFF8000'00000000 through FFFFFFFF'FFFFFFFF, for a total of 256 <a href="/wiki/Tebibyte" class="mw-redirect" title="Tebibyte">TiB</a> of usable virtual address space. This is still 65,536 times larger than the virtual 4 GiB address space of 32-bit machines. This feature eases later scalability to true 64-bit addressing. Many operating systems (including, but not limited to, the <a href="/wiki/Windows_NT" title="Windows NT">Windows NT</a> family) take the higher-addressed half of the address space (named <a href="/wiki/Kernel_space" class="mw-redirect" title="Kernel space">kernel space</a>) for themselves and leave the lower-addressed half (<a href="/wiki/User_space" class="mw-redirect" title="User space">user space</a>) for application code, user mode stacks, heaps, and other data regions.<a href="#cite_note-win-lim-msdn-25">[23]</a> The "canonical address" design ensures that every AMD64 compliant implementation has, in effect, two memory halves: the lower half starts at 00000000'00000000 and "grows upwards" as more virtual address bits become available, while the higher half is "docked" to the top of the address space and grows downwards. Also, enforcing the "canonical form" of addresses by checking the unused address bits prevents their use by the operating system in <a href="/wiki/Tagged_pointer" title="Tagged pointer">tagged pointers</a> as flags, privilege markers, etc., as such use could become problematic when the architecture is extended to implement more virtual address bits. The first versions of Windows for x64 did not even use the full 256 TiB; they were restricted to just 8 TiB of user space and 8 TiB of kernel space.<a href="#cite_note-win-lim-msdn-25">[23]</a> Windows did not support the entire 48-bit address space until <a href="/wiki/Windows_8.1" title="Windows 8.1">Windows 8.1</a>, which was released in October 2013.<a href="#cite_note-win-lim-msdn-25">[23]</a> <div class="mw-heading mw-heading4"><h4 id="Page_table_structure">Page table structure</h4>[<a href="/w/index.php?title=X86-64&action=edit&section=7" title="Edit section: Page table structure">edit</a>]</div> <figure class="mw-halign-right" typeof="mw:File"><a href="/wiki/File:X86_Paging_64bit.svg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/9/9b/X86_Paging_64bit.svg/555px-X86_Paging_64bit.svg.png" decoding="async" width="555" height="263" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/9/9b/X86_Paging_64bit.svg/833px-X86_Paging_64bit.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/9/9b/X86_Paging_64bit.svg/1110px-X86_Paging_64bit.svg.png 2x" data-file-width="873" data-file-height="414" /></a><figcaption></figcaption></figure> The 64-bit addressing mode ("<a href="/wiki/Long_mode" title="Long mode">long mode</a>") is a superset of <a href="/wiki/Physical_Address_Extension" title="Physical Address Extension">Physical Address Extensions</a> (PAE); because of this, <a href="/wiki/Paging" class="mw-redirect" title="Paging">page</a> sizes may be 4 <a href="/wiki/Kibibyte" class="mw-redirect" title="Kibibyte">KiB</a> (212 bytes) or 2 <a href="/wiki/Mebibyte" class="mw-redirect" title="Mebibyte">MiB</a> (221 bytes).<a href="#cite_note-amd-24593-12">[11]</a>: 120  Long mode also supports page sizes of 1 <a href="/wiki/Gibibyte" class="mw-redirect" title="Gibibyte">GiB</a> (230 bytes).<a href="#cite_note-amd-24593-12">[11]</a>: 120  Rather than the three-level <a href="/wiki/Page_table" title="Page table">page table</a> system used by systems in PAE mode, systems running in <a href="/wiki/Long_mode" title="Long mode">long mode</a> use four levels of page table: PAE's Page-Directory Pointer Table is extended from four entries to 512, and an additional Page-Map Level 4 (PML4) Table is added, containing 512 entries in 48-bit implementations.<a href="#cite_note-amd-24593-12">[11]</a>: 131  A full mapping hierarchy of 4 KiB pages for the whole 48-bit space would take a bit more than 512 <a href="/wiki/Gibibyte" class="mw-redirect" title="Gibibyte">GiB</a> of memory (about 0.195% of the 256 TiB virtual space). <dl><dd><table class="wikitable" style="text-align:center"> <caption>64 bit page table entry </caption> <tbody><tr style="border-top:2px solid #777777;"> <th>Bits: </th> <th>63 </th> <th colspan="11">62 … 52 </th> <th colspan="20">51 … 32 </th></tr> <tr style="border-bottom:2px solid #777777;"> <th>Content: </th> <td><a href="/wiki/NX_bit" title="NX bit">NX</a> </td> <td colspan="11" style="background-color:#ccc;">reserved </td> <td colspan="20">Bit 51…32 of base address </td></tr> <tr> <th>Bits: </th> <th colspan="20">31 … 12 </th> <th colspan="3">11 … 9 </th> <th>8 </th> <th>7 </th> <th>6 </th> <th>5 </th> <th>4 </th> <th>3 </th> <th>2 </th> <th>1 </th> <th>0 </th></tr> <tr style="border-bottom:2px solid #777777;"> <th>Content: </th> <td colspan="20">Bit 31…12 of base address </td> <td colspan="3">ign. </td> <td>G </td> <td>PAT </td> <td>D </td> <td>A </td> <td>PCD </td> <td>PWT </td> <td>U/S </td> <td>R/W </td> <td>P </td></tr></tbody></table></dd></dl> Intel has implemented a scheme with a <a href="/wiki/Intel_5-level_paging" title="Intel 5-level paging">5-level page table</a>, which allows Intel 64 processors to support a 57-bit virtual address space.<a href="#cite_note-26">[24]</a> Further extensions may allow full 64-bit virtual address space and physical memory with 12-bit page table descriptors and 16- or 21-bit memory offsets for 64 KiB and 2 MiB page allocation sizes; the page table entry would be expanded to 128 bits to support additional hardware flags for page size and virtual address space size.<a href="#cite_note-27">[25]</a> <div class="mw-heading mw-heading4"><h4 id="Operating_system_limits">Operating system limits</h4>[<a href="/w/index.php?title=X86-64&action=edit&section=8" title="Edit section: Operating system limits">edit</a>]</div> The operating system can also limit the virtual address space. Details, where applicable, are given in the "<a href="#Operating_system_compatibility_and_characteristics">Operating system compatibility and characteristics</a>" section. <div class="mw-heading mw-heading3"><h3 id="Physical_address_space_details">Physical address space details</h3>[<a href="/w/index.php?title=X86-64&action=edit&section=9" title="Edit section: Physical address space details">edit</a>]</div> Current AMD64 processors support a physical address space of up to 248 bytes of RAM, or 256 <a href="/wiki/Tebibyte" class="mw-redirect" title="Tebibyte">TiB</a>.<a href="#cite_note-amd10h-21">[19]</a> However, as of 2020<a class="external text" href="https://en.wikipedia.org/w/index.php?title=X86-64&action=edit">[update]</a>, there were no known x86-64 <a href="/wiki/Motherboard" title="Motherboard">motherboards</a> that support 256 TiB of RAM.<a href="#cite_note-28">[26]</a><a href="#cite_note-29">[27]</a><a href="#cite_note-30">[28]</a><a href="#cite_note-31">[29]</a>[<a href="/wiki/Wikipedia:Verifiability" title="Wikipedia:Verifiability">failed verification</a>] The operating system may place additional limits on the amount of RAM that is usable or supported. Details on this point are given in the "<a href="#Operating_system_compatibility_and_characteristics">Operating system compatibility and characteristics</a>" section of this article. <div class="mw-heading mw-heading3"><h3 id="Operating_modes">Operating modes</h3>[<a href="/w/index.php?title=X86-64&action=edit&section=10" title="Edit section: Operating modes">edit</a>]</div> The architecture has two primary modes of operation: long mode and legacy mode. <table class="wikitable" style="text-align: center;"> <tbody><tr> <th colspan="2">Operating </th> <th rowspan="2"><a href="/wiki/Operating_system" title="Operating system">Operating system</a> required </th> <th rowspan="2">Type of code being run </th> <th colspan="2">Size (in bits) </th> <th rowspan="2">No. of <a href="/wiki/Register_file" title="Register file">general-purpose registers</a> </th></tr> <tr> <th>mode </th> <th>sub-mode </th> <th>addresses </th> <th>operands (default in italics) </th></tr> <tr> <td rowspan="3"><a href="/wiki/Long_mode" title="Long mode">Long mode</a> </td> <td>64-bit mode </td> <td>64-bit OS, 64-bit <a href="/wiki/UEFI" title="UEFI">UEFI</a> firmware, or the previous two interacting via a 64-bit firmware's UEFI interface </td> <td><a href="/wiki/Long_mode" title="Long mode">64-bit</a> </td> <td>64 </td> <td>8, 16, 32, 64 </td> <td>16 </td></tr> <tr> <td rowspan="2">Compatibility mode </td> <td rowspan="2"><a href="/wiki/Bootloader" title="Bootloader">Bootloader</a> or 64-bit OS </td> <td><a href="/wiki/Protected_mode#The_386" title="Protected mode">32-bit</a> </td> <td>32 </td> <td>8, 16, 32 </td> <td>8 </td></tr> <tr> <td><a href="/wiki/Protected_mode#The_286" title="Protected mode">16-bit protected mode</a> </td> <td>16 </td> <td>8, 16, 32 </td> <td>8 </td></tr> <tr> <td rowspan="5">Legacy mode </td> <td rowspan="2"><a href="/wiki/Protected_mode" title="Protected mode">Protected mode</a> </td> <td><a href="/wiki/Bootloader" title="Bootloader">Bootloader</a>, 32-bit OS, 32-bit UEFI firmware, or the latter two interacting via the firmware's UEFI interface </td> <td><a href="/wiki/Protected_mode#The_386" title="Protected mode">32-bit</a> </td> <td>32 </td> <td>8, 16, 32 </td> <td>8 </td></tr> <tr> <td>16-bit protected mode OS </td> <td><a href="/wiki/Protected_mode#The_286" title="Protected mode">16-bit protected mode</a> </td> <td>16 </td> <td>8, 16, 32<a href="#cite_note-opsize-prefix-32">[m 1]</a> </td> <td>8 </td></tr> <tr> <td><a href="/wiki/Virtual_8086_mode" title="Virtual 8086 mode">Virtual 8086 mode</a> </td> <td>16-bit protected mode or 32-bit OS </td> <td>subset of <a href="/wiki/Real_mode" title="Real mode">real mode</a> </td> <td>16 </td> <td>8, 16, 32<a href="#cite_note-opsize-prefix-32">[m 1]</a> </td> <td>8 </td></tr> <tr> <td><a href="/wiki/Unreal_mode" title="Unreal mode">Unreal mode</a> </td> <td><a href="/wiki/Bootloader" title="Bootloader">Bootloader</a> or real mode OS </td> <td><a href="/wiki/Real_mode" title="Real mode">real mode</a> </td> <td>16, 20, 32 </td> <td>8, 16, 32<a href="#cite_note-opsize-prefix-32">[m 1]</a> </td> <td>8 </td></tr> <tr> <td><a href="/wiki/Real_mode" title="Real mode">Real mode</a> </td> <td><a href="/wiki/Bootloader" title="Bootloader">Bootloader</a>, real mode OS, or any OS interfacing with a firmware's <a href="/wiki/BIOS" title="BIOS">BIOS</a> interface<a href="#cite_note-AMIBlog-33">[30]</a> </td> <td><a href="/wiki/Real_mode" title="Real mode">real mode</a> </td> <td>16, 20, <a href="/wiki/A20_line" title="A20 line">21</a> </td> <td>8, 16, 32<a href="#cite_note-opsize-prefix-32">[m 1]</a> </td> <td>8 </td></tr></tbody></table> <style data-mw-deduplicate="TemplateStyles:r1239543626">.mw-parser-output .reflist{margin-bottom:0.5em;list-style-type:decimal}@media screen{.mw-parser-output .reflist{font-size:90%}}.mw-parser-output .reflist .references{font-size:100%;margin-bottom:0;list-style-type:inherit}.mw-parser-output .reflist-columns-2{column-width:30em}.mw-parser-output .reflist-columns-3{column-width:25em}.mw-parser-output .reflist-columns{margin-top:0.3em}.mw-parser-output .reflist-columns ol{margin-top:0}.mw-parser-output .reflist-columns li{page-break-inside:avoid;break-inside:avoid-column}.mw-parser-output .reflist-upper-alpha{list-style-type:upper-alpha}.mw-parser-output .reflist-upper-roman{list-style-type:upper-roman}.mw-parser-output .reflist-lower-alpha{list-style-type:lower-alpha}.mw-parser-output .reflist-lower-greek{list-style-type:lower-greek}.mw-parser-output .reflist-lower-roman{list-style-type:lower-roman}</style><div class="reflist"> <div class="mw-references-wrap"><ol class="references"> <li id="cite_note-opsize-prefix-32">^ <a href="#cite_ref-opsize-prefix_32-0">a</a> <a href="#cite_ref-opsize-prefix_32-1">b</a> <a href="#cite_ref-opsize-prefix_32-2">c</a> <a href="#cite_ref-opsize-prefix_32-3">d</a> Note that 16-bit code written for the 80286 and below does not use 32-bit operand instructions. Code written for the 80386 and above can use the operand-size override prefix (0x66). Normally this prefix is used by protected and long mode code for the purpose of using 16-bit operands, as that code would be running in a code segment with a default operand size of 32 bits. In real mode, the default operand size is 16 bits, so the 0x66 prefix is interpreted differently, changing operand size to 32 bits. </li> </ol></div></div> <figure typeof="mw:File/Thumb"><a href="/wiki/File:AMD64StateDiagram.svg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/e/ef/AMD64StateDiagram.svg/400px-AMD64StateDiagram.svg.png" decoding="async" width="400" height="309" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/e/ef/AMD64StateDiagram.svg/600px-AMD64StateDiagram.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/e/ef/AMD64StateDiagram.svg/800px-AMD64StateDiagram.svg.png 2x" data-file-width="990" data-file-height="765" /></a><figcaption>State diagram of the x86-64 operating modes</figcaption></figure> <div class="mw-heading mw-heading4"><h4 id="Long_mode">Long mode</h4>[<a href="/w/index.php?title=X86-64&action=edit&section=11" title="Edit section: Long mode">edit</a>]</div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/wiki/Long_mode" title="Long mode">Long mode</a></div> Long mode is the architecture's intended primary mode of operation; it is a combination of the processor's native 64-bit mode and a combined 32-bit and 16-bit compatibility mode. It is used by 64-bit operating systems. Under a 64-bit operating system, 64-bit programs run under 64-bit mode, and 32-bit and 16-bit protected mode applications (that do not need to use either real mode or virtual 8086 mode in order to execute at any time) run under compatibility mode. Real-mode programs and programs that use virtual 8086 mode at any time cannot be run in long mode unless those modes are emulated in software.<a href="#cite_note-amd-24593-12">[11]</a>: 11  However, such programs may be started from an operating system running in long mode on processors supporting <a href="/wiki/VT-x" class="mw-redirect" title="VT-x">VT-x</a> or <a href="/wiki/AMD-V" class="mw-redirect" title="AMD-V">AMD-V</a> by creating a virtual processor running in the desired mode. Since the basic <a href="/wiki/Instruction_set" class="mw-redirect" title="Instruction set">instruction set</a> is the same, there is almost no performance penalty for executing protected mode x86 code. This is unlike Intel's <a href="/wiki/IA-64" title="IA-64">IA-64</a>, where differences in the underlying instruction set mean that running 32-bit code must be done either in emulation of x86 (making the process slower) or with a dedicated x86 coprocessor. However, on the x86-64 platform, many x86 applications could benefit from a 64-bit <a href="/wiki/Recompile" class="mw-redirect" title="Recompile">recompile</a>, due to the additional registers in 64-bit code and guaranteed SSE2-based FPU support, which a <a href="/wiki/Compiler" title="Compiler">compiler</a> can use for optimization. However, applications that regularly handle integers wider than 32 bits, such as cryptographic algorithms, will need a rewrite of the code handling the huge integers in order to take advantage of the 64-bit registers. <div class="mw-heading mw-heading4"><h4 id="Legacy_mode">Legacy mode</h4>[<a href="/w/index.php?title=X86-64&action=edit&section=12" title="Edit section: Legacy mode">edit</a>]</div> Legacy mode is the mode that the processor is in when it is not in long mode.<a href="#cite_note-amd-24593-12">[11]</a>: 14  In this mode, the processor acts like an older x86 processor, and only 16-bit and 32-bit code can be executed. Legacy mode allows for a maximum of 32 bit virtual addressing which limits the virtual address space to 4 GiB.<a href="#cite_note-amd-24593-12">[11]</a>: 14 : 24 : 118  64-bit programs cannot be run from legacy mode. <div class="mw-heading mw-heading5"><h5 id="Protected_mode">Protected mode</h5>[<a href="/w/index.php?title=X86-64&action=edit&section=13" title="Edit section: Protected mode">edit</a>]</div> <a href="/wiki/Protected_mode" title="Protected mode">Protected mode</a> is made into a submode of legacy mode.<a href="#cite_note-amd-24593-12">[11]</a>: 14  It is the submode that 32-bit operating systems and 16-bit protected mode operating systems operate in when running on an x86-64 CPU.<a href="#cite_note-amd-24593-12">[11]</a>: 14  <div class="mw-heading mw-heading5"><h5 id="Real_mode">Real mode</h5>[<a href="/w/index.php?title=X86-64&action=edit&section=14" title="Edit section: Real mode">edit</a>]</div> <a href="/wiki/Real_mode" title="Real mode">Real mode</a> is the initial mode of operation when the processor is initialized, and is a submode of legacy mode. It is backwards compatible with the original <a href="/wiki/Intel_8086" title="Intel 8086">Intel 8086</a> and <a href="/wiki/Intel_8088" title="Intel 8088">Intel 8088</a> processors. Real mode is primarily used today by operating system bootloaders, which are required by the architecture to configure <a href="#Physical_address_space_details">virtual memory details</a> before transitioning to higher modes. This mode is also used by any operating system that needs to communicate with the system firmware with a traditional <a href="/wiki/BIOS" title="BIOS">BIOS</a>-style interface.<a href="#cite_note-AMIBlog-33">[30]</a> <div class="mw-heading mw-heading2"><h2 id="Intel_64">Intel 64</h2>[<a href="/w/index.php?title=X86-64&action=edit&section=15" title="Edit section: Intel 64">edit</a>]</div> Intel 64 is Intel's implementation of x86-64, used and implemented in various processors made by Intel. <div class="mw-heading mw-heading3"><h3 id="History_2">History</h3>[<a href="/w/index.php?title=X86-64&action=edit&section=16" title="Edit section: History">edit</a>]</div> Historically, AMD has developed and produced processors with instruction sets patterned after Intel's original designs, but with x86-64, roles were reversed: Intel found itself in the position of adopting the <a href="/wiki/Instruction_set_architecture" title="Instruction set architecture">ISA</a> that AMD created as an extension to Intel's own x86 processor line. Intel's project was originally <a href="/wiki/Codename" class="mw-redirect" title="Codename">codenamed</a> Yamhill<a href="#cite_note-35">[31]</a> (after the <a href="/wiki/Yamhill_River" title="Yamhill River">Yamhill River</a> in Oregon's Willamette Valley). After several years of denying its existence, Intel announced at the February 2004 <a href="/wiki/Intel_Developer_Forum" title="Intel Developer Forum">IDF</a> that the project was indeed underway. Intel's chairman at the time, <a href="/wiki/Craig_Barrett_(chief_executive)" title="Craig Barrett (chief executive)">Craig Barrett</a>, admitted that this was one of their worst-kept secrets.<a href="#cite_note-36">[32]</a><a href="#cite_note-37">[33]</a> Intel's name for this instruction set has changed several times. The name used at the IDF was CT<a href="#cite_note-38">[34]</a> (presumably[<a href="/wiki/Wikipedia:No_original_research" title="Wikipedia:No original research">original research?</a>] for Clackamas Technology, another codename from an <a href="/wiki/Clackamas_River" title="Clackamas River">Oregon river</a>); within weeks they began referring to it as IA-32e (for <a href="/wiki/IA-32" title="IA-32">IA-32</a> extensions) and in March 2004 unveiled the "official" name EM64T (Extended Memory 64 Technology). In late 2006 Intel began instead using the name Intel 64 for its implementation, paralleling AMD's use of the name AMD64.<a href="#cite_note-39">[35]</a> The first processor to implement Intel 64 was the multi-socket processor <a href="/wiki/Xeon" title="Xeon">Xeon</a> code-named <a href="/wiki/Xeon#Nocona_and_Irwindale" title="Xeon">Nocona</a> in June 2004. In contrast, the initial Prescott chips (February 2004) did not enable this feature. Intel subsequently began selling Intel 64-enabled Pentium 4s using the E0 revision of the Prescott core, being sold on the OEM market as the Pentium 4, model F. The E0 revision also adds eXecute Disable (XD) (Intel's name for the <a href="/wiki/NX_bit" title="NX bit">NX bit</a>) to Intel 64, and has been included in then current Xeon code-named Irwindale. Intel's official launch of Intel 64 (under the name EM64T at that time) in mainstream desktop processors was the N0 stepping Prescott-2M. The first Intel <a href="/wiki/Mobile_processor" title="Mobile processor">mobile processor</a> implementing Intel 64 is the <a href="/wiki/Merom_(microprocessor)" title="Merom (microprocessor)">Merom</a> version of the <a href="/wiki/Core_2" class="mw-redirect" title="Core 2">Core 2</a> processor, which was released on July 27, 2006. None of Intel's earlier notebook CPUs (<a href="/wiki/Core_Duo" class="mw-redirect" title="Core Duo">Core Duo</a>, <a href="/wiki/Pentium_M" title="Pentium M">Pentium M</a>, <a href="/wiki/Celeron_M" class="mw-redirect" title="Celeron M">Celeron M</a>, <a href="/wiki/Pentium_4" title="Pentium 4">Mobile Pentium 4</a>) implement Intel 64. <div class="mw-heading mw-heading3"><h3 id="Implementations_2">Implementations</h3>[<a href="/w/index.php?title=X86-64&action=edit&section=17" title="Edit section: Implementations">edit</a>]</div> Intel's processors implementing the Intel64 architecture include the <a href="/wiki/Pentium_4" title="Pentium 4">Pentium 4</a> F-series/5x1 series, 506, and 516, <a href="/wiki/Celeron_D" class="mw-redirect" title="Celeron D">Celeron D</a> models 3x1, 3x6, 355, 347, 352, 360, and 365 and all later <a href="/wiki/Celeron" title="Celeron">Celerons</a>, all models of <a href="/wiki/Xeon" title="Xeon">Xeon</a> since "<a href="/wiki/Xeon#Nocona_and_Irwindale" title="Xeon">Nocona</a>", all models of <a href="/wiki/Pentium_Dual-Core" title="Pentium Dual-Core">Pentium Dual-Core</a> processors since "<a href="/wiki/Merom_(microprocessor)#Merom-2M" title="Merom (microprocessor)">Merom-2M</a>", the <a href="/wiki/Intel_Atom" title="Intel Atom">Atom</a> 230, 330, D410, D425, D510, D525, N450, N455, N470, N475, N550, N570, N2600 and N2800, all versions of the <a href="/wiki/Pentium_D" title="Pentium D">Pentium D</a>, <a href="/wiki/Pentium_Extreme_Edition" class="mw-redirect" title="Pentium Extreme Edition">Pentium Extreme Edition</a>, <a href="/wiki/Core_2" class="mw-redirect" title="Core 2">Core 2</a>, <a href="/wiki/Core_i9" class="mw-redirect" title="Core i9">Core i9</a>, <a href="/wiki/Core_i7" class="mw-redirect" title="Core i7">Core i7</a>, <a href="/wiki/Core_i5" class="mw-redirect" title="Core i5">Core i5</a>, and <a href="/wiki/Core_i3" class="mw-redirect" title="Core i3">Core i3</a> processors, and the <a href="/wiki/Xeon_Phi" title="Xeon Phi">Xeon Phi</a> 7200 series processors. <div class="mw-heading mw-heading3"><h3 id="X86S">X86S</h3>[<a href="/w/index.php?title=X86-64&action=edit&section=18" title="Edit section: X86S">edit</a>]</div> X86S is a simplification of x86-64 proposed by Intel in May 2023 for their "Intel 64" products.<a href="#cite_note-40">[36]</a> The new architecture would remove support for 16-bit and 32-bit operating systems, while 32-bit programs will still run under a 64-bit OS. A CPU would no longer have <a href="#Legacy_mode">legacy mode</a>, and start directly in 64-bit <a href="/wiki/Long_mode" title="Long mode">long mode</a>. There will be a way to switch to <a href="/wiki/5-level_paging" class="mw-redirect" title="5-level paging">5-level paging</a> without going through the unpaged mode. Specific removed features include:<a href="#cite_note-x86-S-41">[37]</a> <style data-mw-deduplicate="TemplateStyles:r1184024115">.mw-parser-output .div-col{margin-top:0.3em;column-width:30em}.mw-parser-output .div-col-small{font-size:90%}.mw-parser-output .div-col-rules{column-rule:1px solid #aaa}.mw-parser-output .div-col dl,.mw-parser-output .div-col ol,.mw-parser-output .div-col ul{margin-top:0}.mw-parser-output .div-col li,.mw-parser-output .div-col dd{page-break-inside:avoid;break-inside:avoid-column}</style><div class="div-col"> <ul><li>Segmentation gates</li> <li>32-bit ring 0 <ul><li>VT-x will no longer emulate this feature</li></ul></li> <li><a href="/wiki/Protection_ring" title="Protection ring">Rings 1 and 2</a></li> <li>Ring 3 I/O port (<link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r886049734">IN/<link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r886049734">OUT) access; see <a href="/wiki/Port-mapped_I/O" class="mw-redirect" title="Port-mapped I/O">port-mapped I/O</a></li> <li>String port I/O (<link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r886049734">INS/<link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r886049734">OUTS)</li> <li><a href="/wiki/Real_mode" title="Real mode">Real mode</a> (including <a href="/wiki/Huge_real_mode" class="mw-redirect" title="Huge real mode">huge real mode</a>), 16-bit protected mode, VM86</li> <li>16-bit addressing mode <ul><li>VT-x will no longer provide unrestricted mode</li></ul></li> <li><a href="/wiki/Intel_8259" title="Intel 8259">8259</a> support; the only <a href="/wiki/Advanced_Programmable_Interrupt_Controller" title="Advanced Programmable Interrupt Controller">APIC</a> supported would be X2APIC</li> <li>Some unused operating system mode bits</li> <li>16-bit and 32-bit Startup <a href="/wiki/Inter-Processor_Interrupt" class="mw-redirect" title="Inter-Processor Interrupt">IPI</a> (SIPI)</li></ul> </div> Intel believes the change follows logically after the removal of the <a href="/wiki/A20_gate" class="mw-redirect" title="A20 gate">A20 gate</a> in 2008 and the removal of 16-bit and 32-bit OS support in Intel firmware in 2020. Support for legacy operating systems would be accomplished via <a href="/wiki/VT-x" class="mw-redirect" title="VT-x">hardware-accelerated virtualization</a> and/or <a href="/wiki/Protection_ring" title="Protection ring">ring 0</a> emulation.<a href="#cite_note-x86-S-41">[37]</a> <div class="mw-heading mw-heading3"><h3 id="Advanced_Performance_Extensions">Advanced Performance Extensions</h3>[<a href="/w/index.php?title=X86-64&action=edit&section=19" title="Edit section: Advanced Performance Extensions">edit</a>]</div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/wiki/X86#APX_(Advanced_Performance_Extensions)" title="X86">X86 § APX (Advanced Performance Extensions)</a></div> Advanced Performance Extensions is a 2023 Intel proposal for new instructions and an additional 16 general-purpose registers. <div class="mw-heading mw-heading2"><h2 id="VIA's_x86-64_implementation">VIA's x86-64 implementation</h2>[<a href="/w/index.php?title=X86-64&action=edit&section=20" title="Edit section: VIA's x86-64 implementation">edit</a>]</div> <a href="/wiki/VIA_Technologies" title="VIA Technologies">VIA Technologies</a> introduced their first implementation of the x86-64 architecture in 2008 after five years of development by its CPU division, <a href="/wiki/Centaur_Technology" title="Centaur Technology">Centaur Technology</a>.<a href="#cite_note-42">[38]</a> Codenamed "Isaiah", the 64-bit architecture was unveiled on January 24, 2008,<a href="#cite_note-43">[39]</a> and launched on May 29 under the <a href="/wiki/VIA_Nano" title="VIA Nano">VIA Nano</a> brand name.<a href="#cite_note-44">[40]</a> The processor supports a number of VIA-specific x86 extensions designed to boost efficiency in low-power appliances. It is expected that the Isaiah architecture will be twice as fast in integer performance and four times as fast in <a href="/wiki/Floating-point" class="mw-redirect" title="Floating-point">floating-point</a> performance as the previous-generation <a href="/wiki/VIA_Esther" class="mw-redirect" title="VIA Esther">VIA Esther</a> at an equivalent <a href="/wiki/Clock_speed" class="mw-redirect" title="Clock speed">clock speed</a>. Power consumption is also expected to be on par with the previous-generation VIA CPUs, with <a href="/wiki/Thermal_design_power" title="Thermal design power">thermal design power</a> ranging from 5 W to 25 W.<a href="#cite_note-45">[41]</a> Being a completely new design, the Isaiah architecture was built with support for features like the x86-64 instruction set and <a href="/wiki/X86_virtualization" title="X86 virtualization">x86 virtualization</a> which were unavailable on its predecessors, the <a href="/wiki/VIA_C7" title="VIA C7">VIA C7</a> line, while retaining their encryption extensions. <div class="mw-heading mw-heading2"><h2 id="Microarchitecture_levels">Microarchitecture levels</h2>[<a href="/w/index.php?title=X86-64&action=edit&section=21" title="Edit section: Microarchitecture levels">edit</a>]</div> In 2020, through a collaboration between AMD, Intel, <a href="/wiki/Red_Hat" title="Red Hat">Red Hat</a>, and <a href="/wiki/SUSE_S.A." title="SUSE S.A.">SUSE</a>, three microarchitecture levels (or feature levels) on top of the x86-64 baseline were defined: x86-64-v2, x86-64-v3, and x86-64-v4.<a href="#cite_note-46">[42]</a><a href="#cite_note-47">[43]</a> These levels define specific features that can be targeted by programmers to provide compile-time optimizations. The features exposed by each level are as follows:<a href="#cite_note-48">[44]</a> <table class="wikitable"> <caption>CPU microarchitecture levels </caption> <tbody><tr> <th>Level name </th> <th>CPU features </th> <th>Example instruction </th> <th>Supported processors </th></tr> <tr> <td rowspan="9">(baseline) also as: x86-64-v1 </td> <td><a href="/wiki/CMOV" class="mw-redirect" title="CMOV">CMOV</a></td> <td>cmov </td> <td rowspan="9"> baseline for all x86-64 CPUs matches the common capabilities between the 2003 AMD AMD64 and the 2004 Intel EM64T initial implementations in the AMD K8 and the Intel Prescott processor families </td></tr> <tr> <td>CX8</td> <td>cmpxchg8b </td></tr> <tr> <td><a href="/wiki/X87" title="X87">FPU</a></td> <td>fld </td></tr> <tr> <td>FXSR</td> <td>fxsave </td></tr> <tr> <td>MMX</td> <td>emms </td></tr> <tr> <td>OSFXSR</td> <td>fxsave </td></tr> <tr> <td>SCE</td> <td>syscall </td></tr> <tr> <td>SSE</td> <td>cvtss2si </td></tr> <tr> <td>SSE2</td> <td>cvtpi2pd </td></tr> <tr> <td rowspan="7">x86-64-v2 </td> <td>CMPXCHG16B</td> <td>cmpxchg16b </td> <td rowspan="7"> Intel <a href="/wiki/Nehalem_(microarchitecture)" title="Nehalem (microarchitecture)">Nehalem</a> and newer Intel "big" cores Intel (Atom) <a href="/wiki/Silvermont" title="Silvermont">Silvermont</a> and newer Intel "small" cores AMD <a href="/wiki/Bulldozer_(microarchitecture)" title="Bulldozer (microarchitecture)">Bulldozer</a> and newer AMD "big" cores AMD <a href="/wiki/Jaguar_(microarchitecture)" title="Jaguar (microarchitecture)">Jaguar</a> <a href="/wiki/VIA_Technologies" title="VIA Technologies">VIA</a> Nano and Eden "C" features match the 2008 Intel Nehalem architecture, excluding Intel-specific instructions </td></tr> <tr> <td>LAHF-SAHF</td> <td>lahf </td></tr> <tr> <td>POPCNT</td> <td>popcnt </td></tr> <tr> <td>SSE3</td> <td>addsubpd </td></tr> <tr> <td>SSE4_1</td> <td>blendpd </td></tr> <tr> <td>SSE4_2</td> <td>pcmpestri </td></tr> <tr> <td>SSSE3</td> <td>pshufb </td></tr> <tr> <td rowspan="9">x86-64-v3 </td> <td>AVX</td> <td>vzeroall </td> <td rowspan="9"> Intel <a href="/wiki/Haswell_(microarchitecture)" title="Haswell (microarchitecture)">Haswell</a> and newer Intel "big" cores (AVX2 enabled models only) Intel (Atom) <a href="/wiki/Gracemont_(microarchitecture)" title="Gracemont (microarchitecture)">Gracemont</a> and newer Intel "small" cores AMD <a href="/wiki/Excavator_(microarchitecture)" title="Excavator (microarchitecture)">Excavator</a> and newer AMD "big" cores <a href="/wiki/QEMU" title="QEMU">QEMU</a> emulation (as of version 7.2)<a href="#cite_note-49">[45]</a><a href="#cite_note-50">[46]</a> features match the 2013 Intel Haswell architecture, excluding Intel-specific instructions </td></tr> <tr> <td>AVX2</td> <td>vpermd </td></tr> <tr> <td>BMI1</td> <td>andn </td></tr> <tr> <td>BMI2</td> <td>bzhi </td></tr> <tr> <td>F16C</td> <td>vcvtph2ps </td></tr> <tr> <td>FMA</td> <td>vfmadd132pd </td></tr> <tr> <td>LZCNT</td> <td>lzcnt </td></tr> <tr> <td>MOVBE</td> <td>movbe </td></tr> <tr> <td>OSXSAVE</td> <td>xgetbv </td></tr> <tr> <td rowspan="5">x86-64-v4 </td> <td>AVX512F</td> <td>kmovw </td> <td rowspan="5"> Intel <a href="/wiki/Skylake_(microarchitecture)" title="Skylake (microarchitecture)">Skylake</a> and newer Intel "big" cores (AVX512 enabled models only) AMD <a href="/wiki/Zen_4" title="Zen 4">Zen 4</a> and newer AMD cores features match the 2017 Intel Skylake-X architecture, excluding Intel-specific instructions </td></tr> <tr> <td>AVX512BW</td> <td>vdbpsadbw </td></tr> <tr> <td>AVX512CD</td> <td>vplzcntd </td></tr> <tr> <td>AVX512DQ</td> <td>vpmullq </td></tr> <tr> <td>AVX512VL</td> <td data-sort-value="" style="background: var(--background-color-interactive, #ececec); color: var(--color-base, inherit); vertical-align: middle; text-align: center;" class="table-na">— </td></tr></tbody></table> The x86-64 microarchitecture feature levels can also be found as AMD64-v1, AMD64-v2 .. or AMD64_v1 .. in settings where the "AMD64" nomenclature is used. These are used as synonyms with the x86-64-vX nomenclature and are thus functionally identical. E.g. the Go language documentation or the Fedora linux distribution. All levels include features found in the previous levels. Instruction set extensions not concerned with general-purpose computation, including <a href="/wiki/AES-NI" class="mw-redirect" title="AES-NI">AES-NI</a> and <a href="/wiki/RDRAND" title="RDRAND">RDRAND</a>, are excluded from the level requirements. <div class="mw-heading mw-heading2"><h2 id="Differences_between_AMD64_and_Intel_64">Differences between AMD64 and Intel 64</h2>[<a href="/w/index.php?title=X86-64&action=edit&section=22" title="Edit section: Differences between AMD64 and Intel 64">edit</a>]</div> Although nearly identical, there are some differences between the two instruction sets in the semantics of a few seldom used machine instructions (or situations), which are mainly used for <a href="/wiki/System_programming" class="mw-redirect" title="System programming">system programming</a>.<a href="#cite_note-trcscott-51">[47]</a> Compilers generally produce <a href="/wiki/Executable" title="Executable">executables</a> (i.e. <a href="/wiki/Machine_code" title="Machine code">machine code</a>) that avoid any differences, at least for ordinary <a href="/wiki/Application_software" title="Application software">application programs</a>. This is therefore of interest mainly to developers of compilers, operating systems and similar, which must deal with individual and special system instructions. <div class="mw-heading mw-heading3"><h3 id="Recent_implementations">Recent implementations</h3>[<a href="/w/index.php?title=X86-64&action=edit&section=23" title="Edit section: Recent implementations">edit</a>]</div> <ul><li>Intel 64's <a href="/wiki/Find_first_set" title="Find first set"><code>BSF</code></a> and <a href="/wiki/Find_first_set" title="Find first set"><code>BSR</code></a> instructions act differently than AMD64's when the source is zero and the operand size is 32 bits. The processor sets the zero flag and leaves the upper 32 bits of the destination undefined.[<a href="/wiki/Wikipedia:Citation_needed" title="Wikipedia:Citation needed"><span title="my testing on Core2 and Skylake show in practice the whole 64-bit register is unmodified; Intel *documents* that the whole register (not just upper bits) is undefined in this case, but in practice implements the same behaviour AMD documents (March 2021)">citation needed</a>] Note that Intel documents that the destination register has an undefined value in this case, but in practice in silicon implements the same behaviour as AMD (destination unmodified). The separate claim about maybe not preserving bits in the upper 32 has not been verified, but has only been ruled out for Core 2 and Skylake,<a href="#cite_note-52">[48]</a> not all Intel microarchitectures like 64-bit Pentium 4 or low-power Atom.</li> <li>AMD64 requires a different microcode update format and control MSRs (model-specific registers), while Intel 64 implements <a href="/wiki/Microcode" title="Microcode">microcode</a> update unchanged from their 32-bit only processors.</li> <li>Intel 64 lacks some MSRs that are considered architectural in AMD64. These include <code>SYSCFG</code>, <code>TOP_MEM</code>, and <code>TOP_MEM2</code>.</li> <li>Intel 64 allows <code>SYSCALL</code>/<code>SYSRET</code> only in 64-bit mode (not in compatibility mode),<a href="#cite_note-53">[49]</a> and allows <code>SYSENTER</code>/<code>SYSEXIT</code> in both modes.<a href="#cite_note-54">[50]</a> AMD64 lacks <code>SYSENTER</code>/<code>SYSEXIT</code> in both sub-modes of <a href="/wiki/Long_mode" title="Long mode">long mode</a>.<a href="#cite_note-amd-24593-12">[11]</a>: 33 </li> <li>In 64-bit mode, near branches with the 66H (operand size override) prefix behave differently. Intel 64 ignores this prefix: the instruction has a 32-bit sign extended offset, and instruction pointer is not truncated. AMD64 uses a 16-bit offset field in the instruction, and clears the top 48 bits of instruction pointer.</li> <li>On Intel 64 but not AMD64, the <code>REX.W</code> prefix can be used with the far-pointer instructions (<code>LFS</code>, <code>LGS</code>, <code>LSS</code>, <code>JMP FAR</code>, <code>CALL FAR</code>) to increase the size of their <a href="/wiki/Far_pointer" title="Far pointer">far pointer</a> argument to 80 bits (64-bit offset + 16-bit segment).</li> <li>When the <code>MOVSXD</code> instruction is executed with a memory source operand and an operand-size of 16 bits, the memory operand will be accessed with a 16-bit read on Intel 64, but a 32-bit read on AMD64.</li> <li>The <code>FCOMI</code>/<code>FCOMIP</code>/<code>FUCOMI</code>/<code>FUCOMIP</code> (x87 floating-point compare) instructions will clear the OF, SF and AF bits of <a href="/wiki/EFLAGS" class="mw-redirect" title="EFLAGS">EFLAGS</a> on Intel 64, but leave these flag bits unmodified on AMD64.</li> <li>For the <code>VMASKMOVPS</code>/<code>VMASKMOVPD</code>/<code>VPMASKMOVD</code>/<code>VPMASKMOVQ</code> (AVX/AVX2 masked move to/from memory) instructions, Intel 64 architecturally guarantees that the instructions will not cause memory faults (e.g. page-faults and segmentation-faults) for any zero-masked lanes, while AMD64 does not provide such a guarantee.</li> <li>Intel 64 lacks the ability to save and restore a reduced (and thus faster) version of the <a href="/wiki/Floating-point" class="mw-redirect" title="Floating-point">floating-point</a> state (involving the <code>FXSAVE</code> and <code>FXRSTOR</code> instructions).[<a href="/wiki/Wikipedia:Please_clarify" title="Wikipedia:Please clarify">clarification needed</a>]</li> <li>AMD processors ever since <a href="/wiki/Opteron" title="Opteron">Opteron</a> Rev. E and <a href="/wiki/Athlon_64" title="Athlon 64">Athlon 64</a> Rev. D have reintroduced limited support for segmentation, via the Long Mode Segment Limit Enable (LMSLE) bit, to ease <a href="/wiki/X86_virtualization#64-bit" title="X86 virtualization">virtualization</a> of 64-bit guests.<a href="#cite_note-55">[51]</a><a href="#cite_note-56">[52]</a> LMLSE support was removed in the Zen 3 processor. <a href="#cite_note-57">[53]</a></li> <li>When returning to a non-canonical address using <code>SYSRET</code>, AMD64 processors execute the general protection fault handler in privilege level 3,<a href="#cite_note-58">[54]</a> while on Intel 64 processors it is executed in privilege level 0.<a href="#cite_note-59">[55]</a></li> <li>The ordering guarantees provided by some memory ordering instructions such as <code>LFENCE</code> and <code>MFENCE</code> differ between Intel 64 and AMD64: <ul><li><code>LFENCE</code> is dispatch-serializing (enabling it to be used as a <a href="/wiki/Speculative_execution" title="Speculative execution">speculation</a> fence) on Intel 64 but is not architecturally guaranteed to be dispatch-serializing on AMD64.<a href="#cite_note-60">[56]</a></li> <li><code>MFENCE</code> is a fully serializing instruction (including instruction fetch serialization) on AMD64 but not Intel 64.</li></ul></li></ul> <div class="mw-heading mw-heading3"><h3 id="Older_implementations">Older implementations</h3>[<a href="/w/index.php?title=X86-64&action=edit&section=24" title="Edit section: Older implementations">edit</a>]</div> <style data-mw-deduplicate="TemplateStyles:r1251242444">.mw-parser-output .ambox{border:1px solid #a2a9b1;border-left:10px solid #36c;background-color:#fbfbfb;box-sizing:border-box}.mw-parser-output .ambox+link+.ambox,.mw-parser-output .ambox+link+style+.ambox,.mw-parser-output .ambox+link+link+.ambox,.mw-parser-output .ambox+.mw-empty-elt+link+.ambox,.mw-parser-output .ambox+.mw-empty-elt+link+style+.ambox,.mw-parser-output .ambox+.mw-empty-elt+link+link+.ambox{margin-top:-1px}html body.mediawiki .mw-parser-output .ambox.mbox-small-left{margin:4px 1em 4px 0;overflow:hidden;width:238px;border-collapse:collapse;font-size:88%;line-height:1.25em}.mw-parser-output .ambox-speedy{border-left:10px solid #b32424;background-color:#fee7e6}.mw-parser-output .ambox-delete{border-left:10px solid #b32424}.mw-parser-output .ambox-content{border-left:10px solid #f28500}.mw-parser-output .ambox-style{border-left:10px solid #fc3}.mw-parser-output .ambox-move{border-left:10px solid #9932cc}.mw-parser-output .ambox-protection{border-left:10px solid #a2a9b1}.mw-parser-output .ambox .mbox-text{border:none;padding:0.25em 0.5em;width:100%}.mw-parser-output .ambox .mbox-image{border:none;padding:2px 0 2px 0.5em;text-align:center}.mw-parser-output .ambox .mbox-imageright{border:none;padding:2px 0.5em 2px 0;text-align:center}.mw-parser-output .ambox .mbox-empty-cell{border:none;padding:0;width:1px}.mw-parser-output .ambox .mbox-image-div{width:52px}@media(min-width:720px){.mw-parser-output .ambox{margin:0 10%}}@media print{body.ns-0 .mw-parser-output .ambox{display:none!important}}</style><table class="box-Update plainlinks metadata ambox ambox-content ambox-Update" role="presentation"><tbody><tr><td class="mbox-image"><div class="mbox-image-div"><img alt="" src="//upload.wikimedia.org/wikipedia/commons/thumb/5/53/Ambox_current_red_Americas.svg/42px-Ambox_current_red_Americas.svg.png" decoding="async" width="42" height="34" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/5/53/Ambox_current_red_Americas.svg/63px-Ambox_current_red_Americas.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/5/53/Ambox_current_red_Americas.svg/84px-Ambox_current_red_Americas.svg.png 2x" data-file-width="360" data-file-height="290" /></div></td><td class="mbox-text"><div class="mbox-text-span">This section needs to be updated. The reason given is: future tense relating to processors that have been out for years, dates with day and month but no year. Please help update this article to reflect recent events or newly available information. (January 2023)</div></td></tr></tbody></table> <ul><li>The AMD64 processors prior to Revision F<a href="#cite_note-61">[57]</a> (distinguished by the switch from <a href="/wiki/DDR_SDRAM" title="DDR SDRAM">DDR</a> to <a href="/wiki/DDR2_SDRAM" title="DDR2 SDRAM">DDR2</a> memory and new sockets <a href="/wiki/Socket_AM2" title="Socket AM2">AM2</a>, <a href="/wiki/Socket_F" title="Socket F">F</a> and <a href="/wiki/Socket_S1" title="Socket S1">S1</a>) of 2006 lacked the <code>CMPXCHG16B</code> instruction, which is an extension of the <code>CMPXCHG8B</code> instruction present on most post-<a href="/wiki/80486" class="mw-redirect" title="80486">80486</a> processors. Similar to <code>CMPXCHG8B</code>, <code>CMPXCHG16B</code> allows for <a href="/wiki/Atomic_operation" class="mw-redirect" title="Atomic operation">atomic operations</a> on octa-words (128-bit values). This is useful for parallel algorithms that use <a href="/wiki/Compare_and_swap" class="mw-redirect" title="Compare and swap">compare and swap</a> on data larger than the size of a pointer, common in <a href="/wiki/Lock-free_and_wait-free_algorithms" class="mw-redirect" title="Lock-free and wait-free algorithms">lock-free and wait-free algorithms</a>. Without <code>CMPXCHG16B</code> one must use workarounds, such as a <a href="/wiki/Critical_section" title="Critical section">critical section</a> or alternative lock-free approaches.<a href="#cite_note-62">[58]</a> Its absence also prevents 64-bit <a href="/wiki/Microsoft_Windows" title="Microsoft Windows">Windows</a> prior to Windows 8.1 from having a <a href="/wiki/User-mode" class="mw-redirect" title="User-mode">user-mode</a> address space larger than 8 <a href="/wiki/Tebibyte" class="mw-redirect" title="Tebibyte">TiB</a>.<a href="#cite_note-63">[59]</a> The 64-bit version of <a href="/wiki/Windows_8.1" title="Windows 8.1">Windows 8.1</a> requires the instruction.<a href="#cite_note-CPUinsts8.1-64">[60]</a></li> <li>Early AMD64 and Intel 64 CPUs lacked <code>LAHF</code> and <code>SAHF</code> instructions in 64-bit mode. AMD introduced these instructions (also in 64-bit mode) with their <a href="/wiki/90_nm_process" title="90 nm process">90 nm</a> (revision D) processors, starting with Athlon 64 in October 2004.<a href="#cite_note-65">[61]</a><a href="#cite_note-66">[62]</a> Intel introduced the instructions in October 2005 with the 0F47h and later revisions of <a href="/wiki/NetBurst" title="NetBurst">NetBurst</a>.<a href="#cite_note-73">[68]</a> The 64-bit version of Windows 8.1 requires this feature.<a href="#cite_note-CPUinsts8.1-64">[60]</a></li> <li>Early Intel CPUs with Intel 64 also lack the <a href="/wiki/NX_bit" title="NX bit">NX bit</a> of the AMD64 architecture. It was added in the stepping E0 (0F41h) Pentium 4 in October 2004.<a href="#cite_note-74">[69]</a> This feature is required by all versions of Windows 8.</li> <li>Early Intel 64 implementations had a 36-bit (64 GiB) physical addressing of memory while original AMD64 implementations had a 40-bit (1 <a href="/wiki/Tebibyte" class="mw-redirect" title="Tebibyte">TiB</a>) physical addressing. Intel used the 40-bit physical addressing first on Xeon MP (<a href="/wiki/Xeon#Cranford_and_Potomac" title="Xeon">Potomac</a>), launched on 29 March 2005.<a href="#cite_note-75">[70]</a> The difference is not a difference of the user-visible ISAs. In 2007 <a href="/wiki/AMD_10h" title="AMD 10h">AMD 10h</a>-based Opteron was the first to provide a 48-bit (256 TiB) physical address space.<a href="#cite_note-76">[71]</a><a href="#cite_note-77">[72]</a> Intel 64's physical addressing was extended to 44 bits (16 TiB) in Nehalem-EX in 2010<a href="#cite_note-78">[73]</a> and to 46 bits (64 TiB) in Sandy Bridge E in 2011.<a href="#cite_note-79">[74]</a><a href="#cite_note-80">[75]</a> With the Ice Lake 3rd gen Xeon Scalable processors, Intel increased the virtual addressing to 57 bits (128 <a href="/wiki/Pebibyte" class="mw-redirect" title="Pebibyte">PiB</a>) and physical to 52 bits (4 PiB) in 2021, necessitating a <a href="/wiki/Intel_5-level_paging" title="Intel 5-level paging">5-level paging</a>.<a href="#cite_note-81">[76]</a> The following year AMD64 added the same in 4th generation <a href="/wiki/EPYC" class="mw-redirect" title="EPYC">EPYC</a> (Genoa).<a href="#cite_note-82">[77]</a> Non-server CPUs retain smaller address spaces for longer.</li></ul> <div class="mw-heading mw-heading2"><h2 id="Adoption">Adoption</h2>[<a href="/w/index.php?title=X86-64&action=edit&section=25" title="Edit section: Adoption">edit</a>]</div> <figure typeof="mw:File/Thumb"><a href="/wiki/File:Processor_families_in_TOP500_supercomputers.svg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/e/ef/Processor_families_in_TOP500_supercomputers.svg/350px-Processor_families_in_TOP500_supercomputers.svg.png" decoding="async" width="350" height="248" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/e/ef/Processor_families_in_TOP500_supercomputers.svg/525px-Processor_families_in_TOP500_supercomputers.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/e/ef/Processor_families_in_TOP500_supercomputers.svg/700px-Processor_families_in_TOP500_supercomputers.svg.png 2x" data-file-width="1232" data-file-height="873" /></a><figcaption>An area chart showing the representation of different families of microprocessors in the TOP500 supercomputer ranking list, from 1993 to 2020<a href="#cite_note-83">[78]</a></figcaption></figure> In <a href="/wiki/Supercomputer" title="Supercomputer">supercomputers</a> tracked by <a href="/wiki/TOP500" title="TOP500">TOP500</a>, the appearance of 64-bit extensions for the x86 architecture enabled 64-bit x86 processors by AMD and Intel to replace most RISC processor architectures previously used in such systems (including <a href="/wiki/PA-RISC" title="PA-RISC">PA-RISC</a>, <a href="/wiki/SPARC" title="SPARC">SPARC</a>, <a href="/wiki/DEC_Alpha" title="DEC Alpha">Alpha</a> and others), as well as 32-bit x86, even though Intel itself initially tried unsuccessfully to replace x86 with a new incompatible 64-bit architecture in the <a href="/wiki/Itanium" title="Itanium">Itanium</a> processor. As of 2023<a class="external text" href="https://en.wikipedia.org/w/index.php?title=X86-64&action=edit">[update]</a>, a <a href="/wiki/Hewlett_Packard_Enterprise" title="Hewlett Packard Enterprise">HPE</a> <a href="/wiki/Epyc" title="Epyc">EPYC</a>-based supercomputer called <a href="/wiki/Frontier_(supercomputer)" title="Frontier (supercomputer)">Frontier</a> is number one. The first ARM-based supercomputer appeared on the list in 2018<a href="#cite_note-84">[79]</a> and, in recent years, non-CPU architecture co-processors (<a href="/wiki/General-purpose_computing_on_graphics_processing_units" title="General-purpose computing on graphics processing units">GPGPU</a>) have also played a big role in performance. Intel's <a href="/wiki/Xeon_Phi#Knights_Corner" title="Xeon Phi">Xeon Phi "Knights Corner"</a> coprocessors, which implement a subset of x86-64 with some vector extensions,<a href="#cite_note-85">[80]</a> are also used, along with x86-64 processors, in the <a href="/wiki/Tianhe-2" title="Tianhe-2">Tianhe-2</a> supercomputer.<a href="#cite_note-86">[81]</a> <div style="clear:both;" class=""></div> <div class="mw-heading mw-heading2"><h2 id="Operating_system_compatibility_and_characteristics">Operating system compatibility and characteristics</h2>[<a href="/w/index.php?title=X86-64&action=edit&section=26" title="Edit section: Operating system compatibility and characteristics">edit</a>]</div> The following operating systems and releases support the x86-64 architecture in <a href="/wiki/Long_mode" title="Long mode">long mode</a>. <div class="mw-heading mw-heading3"><h3 id="BSD">BSD</h3>[<a href="/w/index.php?title=X86-64&action=edit&section=27" title="Edit section: BSD">edit</a>]</div> <div class="mw-heading mw-heading4"><h4 id="DragonFly_BSD">DragonFly BSD</h4>[<a href="/w/index.php?title=X86-64&action=edit&section=28" title="Edit section: DragonFly BSD">edit</a>]</div> Preliminary infrastructure work was started in February 2004 for a x86-64 port.<a href="#cite_note-dfly-amd64-prelim-87">[82]</a> This development later stalled. Development started again during July 2007<a href="#cite_note-dfly-amd64-noah-88">[83]</a> and continued during <a href="/wiki/Google_Summer_of_Code" title="Google Summer of Code">Google Summer of Code</a> 2008 and SoC 2009.<a href="#cite_note-dfly-amd64-soc2008-89">[84]</a><a href="#cite_note-dfly-amd64-soc2009-90">[85]</a> The first official release to contain x86-64 support was version 2.4.<a href="#cite_note-dflyamd64-release-91">[86]</a> <div class="mw-heading mw-heading4"><h4 id="FreeBSD">FreeBSD</h4>[<a href="/w/index.php?title=X86-64&action=edit&section=29" title="Edit section: FreeBSD">edit</a>]</div> <a href="/wiki/FreeBSD" title="FreeBSD">FreeBSD</a> first added x86-64 support under the name "amd64" as an experimental architecture in 5.1-RELEASE in June 2003. It was included as a standard distribution architecture as of 5.2-RELEASE in January 2004. Since then, FreeBSD has designated it as a Tier 1 platform. The 6.0-RELEASE version cleaned up some quirks with running x86 executables under amd64, and most drivers work just as they do on the x86 architecture. Work is currently being done to integrate more fully the x86 <a href="/wiki/Application_binary_interface" title="Application binary interface">application binary interface</a> (ABI), in the same manner as the Linux 32-bit ABI compatibility currently works. <div class="mw-heading mw-heading4"><h4 id="NetBSD">NetBSD</h4>[<a href="/w/index.php?title=X86-64&action=edit&section=30" title="Edit section: NetBSD">edit</a>]</div> x86-64 architecture support was first committed to the <a href="/wiki/NetBSD" title="NetBSD">NetBSD</a> source tree on June 19, 2001. As of NetBSD 2.0, released on December 9, 2004, NetBSD/amd64 is a fully integrated and supported port. 32-bit code is still supported in 64-bit mode, with a netbsd-32 kernel compatibility layer for 32-bit syscalls. The NX bit is used to provide non-executable stack and heap with per-page granularity (segment granularity being used on 32-bit x86). <div class="mw-heading mw-heading4"><h4 id="OpenBSD">OpenBSD</h4>[<a href="/w/index.php?title=X86-64&action=edit&section=31" title="Edit section: OpenBSD">edit</a>]</div> <a href="/wiki/OpenBSD" title="OpenBSD">OpenBSD</a> has supported AMD64 since OpenBSD 3.5, released on May 1, 2004. Complete in-tree implementation of AMD64 support was achieved prior to the hardware's initial release because AMD had loaned several machines for the project's <a href="/wiki/Hackathon" title="Hackathon">hackathon</a> that year. OpenBSD developers have taken to the platform because of its support for the <a href="/wiki/NX_bit" title="NX bit">NX bit</a>, which allowed for an easy implementation of the <a href="/wiki/W%5EX" title="W^X">W^X</a> feature. The code for the AMD64 port of OpenBSD also runs on Intel 64 processors which contains cloned use of the AMD64 extensions, but since Intel left out the page table NX bit in early Intel 64 processors, there is no W^X capability on those Intel CPUs; later Intel 64 processors added the NX bit under the name "XD bit". <a href="/wiki/Symmetric_multiprocessing" title="Symmetric multiprocessing">Symmetric multiprocessing</a> (SMP) works on OpenBSD's AMD64 port, starting with release 3.6 on November 1, 2004. <div class="mw-heading mw-heading3"><h3 id="DOS">DOS</h3>[<a href="/w/index.php?title=X86-64&action=edit&section=32" title="Edit section: DOS">edit</a>]</div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1251242444"><table class="box-More_citations_needed plainlinks metadata ambox ambox-content ambox-Refimprove" role="presentation"><tbody><tr><td class="mbox-image"><div class="mbox-image-div"><a href="/wiki/File:Question_book-new.svg" class="mw-file-description"><img alt="" src="//upload.wikimedia.org/wikipedia/en/thumb/9/99/Question_book-new.svg/50px-Question_book-new.svg.png" decoding="async" width="50" height="39" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/en/thumb/9/99/Question_book-new.svg/75px-Question_book-new.svg.png 1.5x, //upload.wikimedia.org/wikipedia/en/thumb/9/99/Question_book-new.svg/100px-Question_book-new.svg.png 2x" data-file-width="512" data-file-height="399" /></a></div></td><td class="mbox-text"><div class="mbox-text-span">This article needs additional citations for <a href="/wiki/Wikipedia:Verifiability" title="Wikipedia:Verifiability">verification</a>. Please help <a href="/wiki/Special:EditPage/X86-64" title="Special:EditPage/X86-64">improve this article</a> by <a href="/wiki/Help:Referencing_for_beginners" title="Help:Referencing for beginners">adding citations to reliable sources</a>. Unsourced material may be challenged and removed. Find sources: <a rel="nofollow" class="external text" href="https://www.google.com/search?as_eq=wikipedia&q=%22X86-64%22">"X86-64"</a> – <a rel="nofollow" class="external text" href="https://www.google.com/search?tbm=nws&q=%22X86-64%22+-wikipedia&tbs=ar:1">news</a> · <a rel="nofollow" class="external text" href="https://www.google.com/search?&q=%22X86-64%22&tbs=bkt:s&tbm=bks">newspapers</a> · <a rel="nofollow" class="external text" href="https://www.google.com/search?tbs=bks:1&q=%22X86-64%22+-wikipedia">books</a> · <a rel="nofollow" class="external text" href="https://scholar.google.com/scholar?q=%22X86-64%22">scholar</a> · <a rel="nofollow" class="external text" href="https://www.jstor.org/action/doBasicSearch?Query=%22X86-64%22&acc=on&wc=on">JSTOR</a> (December 2022) (<a href="/wiki/Help:Maintenance_template_removal" title="Help:Maintenance template removal">Learn how and when to remove this message</a>)</div></td></tr></tbody></table> It is possible to enter <a href="/wiki/Long_mode" title="Long mode">long mode</a> under <a href="/wiki/DOS" title="DOS">DOS</a> without a DOS extender,<a href="#cite_note-92">[87]</a> but the user must return to real mode in order to call BIOS or DOS interrupts. It may also be possible to enter <a href="/wiki/Long_mode" title="Long mode">long mode</a> with a <a href="/wiki/DOS_extender" title="DOS extender">DOS extender</a> similar to <a href="/wiki/DOS/4GW" class="mw-redirect" title="DOS/4GW">DOS/4GW</a>, but more complex since x86-64 lacks <a href="/wiki/Virtual_8086_mode" title="Virtual 8086 mode">virtual 8086 mode</a>. DOS itself is not aware of that, and no benefits should be expected unless running DOS in an emulation with an adequate virtualization driver backend, for example: the mass storage interface. <div class="mw-heading mw-heading3"><h3 id="Linux">Linux</h3>[<a href="/w/index.php?title=X86-64&action=edit&section=33" title="Edit section: Linux">edit</a>]</div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">See also: <a href="/wiki/Comparison_of_Linux_distributions#Instruction_set_architecture_support" title="Comparison of Linux distributions">Comparison of Linux distributions § Instruction set architecture support</a></div> <a href="/wiki/Linux" title="Linux">Linux</a> was the first operating system kernel to run the x86-64 architecture in <a href="/wiki/Long_mode" title="Long mode">long mode</a>, starting with the 2.4 version in 2001 (preceding the hardware's availability).<a href="#cite_note-93">[88]</a><a href="#cite_note-94">[89]</a> Linux also provides backward compatibility for running 32-bit executables. This permits programs to be recompiled into long mode while retaining the use of 32-bit programs. Current Linux distributions ship with x86-64-native kernels and <a href="/wiki/Userland_(computing)" class="mw-redirect" title="Userland (computing)">userlands</a>. Some, such as <a href="/wiki/Arch_Linux" title="Arch Linux">Arch Linux</a>,<a href="#cite_note-95">[90]</a> <a href="/wiki/SUSE_Linux" class="mw-redirect" title="SUSE Linux">SUSE</a>, <a href="/wiki/Mandriva_Linux" title="Mandriva Linux">Mandriva</a>, and <a href="/wiki/Debian" title="Debian">Debian</a>, allow users to install a set of 32-bit components and libraries when installing off a 64-bit distribution medium, thus allowing most existing 32-bit applications to run alongside the 64-bit OS. <a href="/wiki/X32_ABI" title="X32 ABI">x32 ABI</a> (Application Binary Interface), introduced in Linux 3.4, allows programs compiled for the x32 ABI to run in the 64-bit mode of x86-64 while only using 32-bit pointers and data fields.<a href="#cite_note-x32ABIHOnline-96">[91]</a><a href="#cite_note-x32ABILinuxPlumbers-97">[92]</a><a href="#cite_note-x32ABIDevelopmentGroup-98">[93]</a> Though this limits the program to a virtual address space of 4 GiB it also decreases the memory footprint of the program and in some cases can allow it to run faster.<a href="#cite_note-x32ABIHOnline-96">[91]</a><a href="#cite_note-x32ABILinuxPlumbers-97">[92]</a><a href="#cite_note-x32ABIDevelopmentGroup-98">[93]</a> 64-bit Linux allows up to 128 <a href="/wiki/Tebibyte" class="mw-redirect" title="Tebibyte">TiB</a> of virtual address space for individual processes, and can address approximately 64 TiB of physical memory, subject to processor and system limitations,<a href="#cite_note-DebianAMD64-99">[94]</a> or up to 128 PiB (virtual) and 4 PiB (physical) with 5-level paging enabled.<a href="#cite_note-Kernel5LevelPaging-100">[95]</a> <div class="mw-heading mw-heading3"><h3 id="macOS">macOS</h3>[<a href="/w/index.php?title=X86-64&action=edit&section=34" title="Edit section: macOS">edit</a>]</div> Mac OS X 10.4.7 and higher versions of <a href="/wiki/Mac_OS_X_Tiger" title="Mac OS X Tiger">Mac OS X 10.4</a> run 64-bit command-line tools using the POSIX and math libraries on 64-bit Intel-based machines, just as all versions of Mac OS X 10.4 and 10.5 run them on 64-bit PowerPC machines. No other libraries or frameworks work with 64-bit applications in Mac OS X 10.4.<a href="#cite_note-101">[96]</a> The kernel, and all kernel extensions, are 32-bit only. <a href="/wiki/Mac_OS_X_Leopard" title="Mac OS X Leopard">Mac OS X 10.5</a> supports 64-bit GUI applications using <a href="/wiki/Cocoa_(API)" title="Cocoa (API)">Cocoa</a>, <a href="/wiki/Quartz_(graphics_layer)" title="Quartz (graphics layer)">Quartz</a>, <a href="/wiki/OpenGL" title="OpenGL">OpenGL</a>, and <a href="/wiki/X11" class="mw-redirect" title="X11">X11</a> on 64-bit Intel-based machines, as well as on 64-bit <a href="/wiki/PowerPC" title="PowerPC">PowerPC</a> machines.<a href="#cite_note-102">[97]</a> All non-GUI libraries and frameworks also support 64-bit applications on those platforms. The kernel, and all kernel extensions, are 32-bit only. <a href="/wiki/Mac_OS_X_Snow_Leopard" title="Mac OS X Snow Leopard">Mac OS X 10.6</a> is the first version of <a href="/wiki/MacOS" title="MacOS">macOS</a> that supports a 64-bit <a href="/wiki/Kernel_(operating_system)" title="Kernel (operating system)">kernel</a>. However, not all 64-bit computers can run the 64-bit kernel, and not all 64-bit computers that can run the 64-bit kernel will do so by default.<a href="#cite_note-103">[98]</a> The 64-bit kernel, like the 32-bit kernel, supports 32-bit applications; both kernels also support 64-bit applications. 32-bit applications have a virtual address space limit of 4 GiB under either kernel.<a href="#cite_note-arstechnicaMacOSX64bit-104">[99]</a><a href="#cite_note-Apple64Bit-105">[100]</a> The 64-bit kernel does not support 32-bit <a href="/wiki/Loadable_kernel_module" title="Loadable kernel module">kernel extensions</a>, and the 32-bit kernel does not support 64-bit kernel extensions. <a href="/wiki/OS_X_Mountain_Lion" title="OS X Mountain Lion">OS X 10.8</a> includes only the 64-bit kernel, but continues to support 32-bit applications; it does not support 32-bit kernel extensions, however. <a href="/wiki/MacOS_Catalina" title="MacOS Catalina">macOS 10.15</a> includes only the 64-bit kernel and no longer supports 32-bit applications. This removal of support has presented a problem for <a href="/wiki/WineHQ" class="mw-redirect" title="WineHQ">WineHQ</a> (and the commercial version <a href="/wiki/CrossOver" class="mw-redirect" title="CrossOver">CrossOver</a>), as it needs to still be able to run 32-bit Windows applications. The solution, termed wine32on64, was to add <a href="/wiki/Thunk" title="Thunk">thunks</a> that bring the CPU in and out of 32-bit compatibility mode in the nominally 64-bit application.<a href="#cite_note-106">[101]</a><a href="#cite_note-107">[102]</a> macOS uses the <a href="/wiki/Universal_binary" title="Universal binary">universal binary</a> format to package 32- and 64-bit versions of application and library code into a single file; the most appropriate version is automatically selected at load time. In Mac OS X 10.6, the universal binary format is also used for the kernel and for those kernel extensions that support both 32-bit and 64-bit kernels. <div class="mw-heading mw-heading3"><h3 id="Solaris">Solaris</h3>[<a href="/w/index.php?title=X86-64&action=edit&section=35" title="Edit section: Solaris">edit</a>]</div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">See also: <a href="/wiki/Illumos" title="Illumos">illumos</a></div> <a href="/wiki/Solaris_(operating_system)" class="mw-redirect" title="Solaris (operating system)">Solaris</a> 10 and later releases support the x86-64 architecture. For Solaris 10, just as with the <a href="/wiki/SPARC" title="SPARC">SPARC</a> architecture, there is only one operating system image, which contains a 32-bit kernel and a 64-bit kernel; this is labeled as the "x64/x86" DVD-ROM image. The default behavior is to boot a 64-bit kernel, allowing both 64-bit and existing or new 32-bit executables to be run. A 32-bit kernel can also be manually selected, in which case only 32-bit executables will run. The <code>isainfo</code> command can be used to determine if a system is running a 64-bit kernel. For Solaris 11, only the 64-bit kernel is provided. However, the 64-bit kernel supports both 32- and 64-bit executables, libraries, and system calls. <div class="mw-heading mw-heading3"><h3 id="Windows">Windows</h3>[<a href="/w/index.php?title=X86-64&action=edit&section=36" title="Edit section: Windows">edit</a>]</div> x64 editions of Microsoft Windows client and server—<a href="/wiki/Windows_XP_Professional_x64_Edition" title="Windows XP Professional x64 Edition">Windows XP Professional x64 Edition</a> and <a href="/wiki/Windows_Server_2003" title="Windows Server 2003">Windows Server 2003</a> x64 Edition—were released in March 2005.<a href="#cite_note-108">[103]</a> Internally they are actually the same build (5.2.3790.1830 SP1),<a href="#cite_note-109">[104]</a><a href="#cite_note-110">[105]</a> as they share the same source base and operating system binaries, so even system updates are released in unified packages, much in the manner as Windows 2000 Professional and Server editions for x86. <a href="/wiki/Windows_Vista" title="Windows Vista">Windows Vista</a>, which also has many different editions, was released in January 2007. <a href="/wiki/Windows_7" title="Windows 7">Windows 7</a> was released in July 2009. <a href="/wiki/Windows_Server_2008_R2" title="Windows Server 2008 R2">Windows Server 2008 R2</a> was sold in only x64 and Itanium editions; later versions of Windows Server only offer an x64 edition. Versions of Windows for x64 prior to Windows 8.1 and Windows Server 2012 R2 offer the following: <ul><li>8 TiB of virtual address space per process, accessible from both user mode and kernel mode, referred to as the user mode address space. An x64 program can use all of this, subject to backing store limits on the system, and provided it is linked with the "large address aware" option, which is present by default.<a href="#cite_note-VSdocLAA-111">[106]</a> This is a 4096-fold increase over the default 2 GiB user-mode virtual address space offered by 32-bit Windows.<a href="#cite_note-Pietrek64BitWindowsProgramming-112">[107]</a><a href="#cite_note-MicrosoftMoveTox64-113">[108]</a></li> <li>8 TiB of kernel mode virtual address space for the operating system.<a href="#cite_note-Pietrek64BitWindowsProgramming-112">[107]</a> As with the user mode address space, this is a 4096-fold increase over 32-bit Windows versions. The increased space primarily benefits the file system cache and kernel mode "heaps" (non-paged pool and paged pool). Windows only uses a total of 16 TiB out of the 256 TiB implemented by the processors because early AMD64 processors lacked a <code>CMPXCHG16B</code> instruction.<a href="#cite_note-114">[109]</a></li></ul> Under Windows 8.1 and Windows Server 2012 R2, both user mode and kernel mode virtual address spaces have been extended to 128 TiB.<a href="#cite_note-win-lim-msdn-25">[23]</a> These versions of Windows will not install on processors that lack the <code>CMPXCHG16B</code> instruction. The following additional characteristics apply to all x64 versions of Windows: <ul><li>Ability to run existing 32-bit applications (<code>.exe</code> programs) and dynamic link libraries (<code>.dll</code>s) using <a href="/wiki/WoW64" title="WoW64">WoW64</a> if WoW64 is supported on that version. Furthermore, a 32-bit program, if it was linked with the "large address aware" option,<a href="#cite_note-VSdocLAA-111">[106]</a> can use up to 4 GiB of virtual address space in 64-bit Windows, instead of the default 2 GiB (optional 3 GiB with <code>/3GB</code> boot option and "large address aware" link option) offered by 32-bit Windows.<a href="#cite_note-64-bitProgrammingGameDevelopers-115">[110]</a> Unlike the use of the <code>/3GB</code> boot option on x86, this does not reduce the kernel mode virtual address space available to the operating system. 32-bit applications can, therefore, benefit from running on x64 Windows even if they are not recompiled for x86-64.</li> <li>Both 32- and 64-bit applications, if not linked with "large address aware", are limited to 2 GiB of virtual address space.</li> <li>Ability to use up to 128 GiB (Windows XP/Vista), 192 GiB (Windows 7), 512 GiB (Windows 8), 1 TiB (Windows Server 2003), 2 TiB (Windows Server 2008/Windows 10), 4 TiB (Windows Server 2012), or 24 TiB (Windows Server 2016/2019) of physical random access memory (RAM).<a href="#cite_note-116">[111]</a></li> <li><a href="/wiki/LLP64" class="mw-redirect" title="LLP64">LLP64</a> data model: in C/C++, "int" and "long" types are 32 bits wide, "long long" is 64 bits, while pointers and types derived from pointers are 64 bits wide.</li> <li>Kernel mode device drivers must be 64-bit versions; there is no way to run 32-bit kernel mode executables within the 64-bit operating system. User mode device drivers can be either 32-bit or 64-bit.</li> <li>16-bit Windows (Win16) and DOS applications will not run on x86-64 versions of Windows due to the removal of the <a href="/wiki/Virtual_DOS_machine" title="Virtual DOS machine">virtual DOS machine</a> subsystem (NTVDM) which relied upon the ability to use virtual 8086 mode. Virtual 8086 mode cannot be entered while running in long mode.</li> <li>Full implementation of the <a href="/wiki/NX_bit" title="NX bit">NX</a> (No Execute) page protection feature. This is also implemented on recent 32-bit versions of Windows when they are started in PAE mode.</li> <li>Instead of FS segment descriptor on x86 versions of the <a href="/wiki/Windows_NT" title="Windows NT">Windows NT</a> family, GS segment descriptor is used to point to two operating system defined structures: Thread Information Block (NT_TIB) in user mode and Processor Control Region (KPCR) in kernel mode. Thus, for example, in user mode <code>GS:0</code> is the address of the first member of the Thread Information Block. Maintaining this convention made the x86-64 port easier, but required AMD to retain the function of the FS and GS segments in long mode – even though segmented addressing per se is not really used by any modern operating system.<a href="#cite_note-Pietrek64BitWindowsProgramming-112">[107]</a></li> <li>Early reports claimed that the operating system scheduler would not save and restore the <a href="/wiki/X87" title="X87">x87</a> FPU machine state across thread context switches. Observed behavior shows that this is not the case: the x87 state is saved and restored, except for kernel mode-only threads (a limitation that exists in the 32-bit version as well). The most recent documentation available from Microsoft states that the x87/<a href="/wiki/MMX_(instruction_set)" title="MMX (instruction set)">MMX</a>/<a href="/wiki/3DNow!" title="3DNow!">3DNow!</a> instructions may be used in long mode, but that they are deprecated and may cause compatibility problems in the future.<a href="#cite_note-64-bitProgrammingGameDevelopers-115">[110]</a> (3DNow! is no longer available on AMD processors, with the exception of the <code>PREFETCH</code> and <code>PREFETCHW</code> instructions,<a href="#cite_note-117">[112]</a> which are also supported on Intel processors as of <a href="/wiki/Broadwell_(microarchitecture)" title="Broadwell (microarchitecture)">Broadwell</a>.)</li> <li>Some components like <a href="/wiki/Jet_Database_Engine" class="mw-redirect" title="Jet Database Engine">Jet Database Engine</a> and <a href="/wiki/Data_Access_Objects" class="mw-redirect" title="Data Access Objects">Data Access Objects</a> will not be ported to 64-bit architectures such as x86-64 and IA-64.<a href="#cite_note-118">[113]</a><a href="#cite_note-119">[114]</a><a href="#cite_note-120">[115]</a></li> <li><a href="/wiki/Microsoft_Visual_Studio" class="mw-redirect" title="Microsoft Visual Studio">Microsoft Visual Studio</a> can compile <a href="/wiki/Native_code" class="mw-redirect" title="Native code">native applications</a> to target either the x86-64 architecture, which can run only on 64-bit Microsoft Windows, or the <a href="/wiki/IA-32" title="IA-32">IA-32</a> architecture, which can run as a 32-bit application on 32-bit Microsoft Windows or 64-bit Microsoft Windows in <a href="/wiki/WoW64" title="WoW64">WoW64</a> emulation mode. <a href="/wiki/Managed_code" title="Managed code">Managed applications</a> can be compiled either in IA-32, x86-64 or AnyCPU modes. Software created in the first two modes behave like their IA-32 or x86-64 native code counterparts respectively; When using the AnyCPU mode, however, applications in 32-bit versions of Microsoft Windows run as 32-bit applications, while they run as a 64-bit application in 64-bit editions of Microsoft Windows.</li></ul> <div class="mw-heading mw-heading2"><h2 id="Video_game_consoles">Video game consoles</h2>[<a href="/w/index.php?title=X86-64&action=edit&section=37" title="Edit section: Video game consoles">edit</a>]</div> Both the <a href="/wiki/PlayStation_4" title="PlayStation 4">PlayStation 4</a> and <a href="/wiki/Xbox_One" title="Xbox One">Xbox One</a>, and all variants of those consoles, incorporate AMD x86-64 processors, based on the <a href="/wiki/Jaguar_(microarchitecture)" title="Jaguar (microarchitecture)">Jaguar</a> <a href="/wiki/Microarchitecture" title="Microarchitecture">microarchitecture</a>.<a href="#cite_note-XboxOneMay2013Anandtechcomparison-121">[116]</a><a href="#cite_note-XboxOneMay2013SpecGameinformer-122">[117]</a> Firmware and games are written in x86-64 code; no legacy x86 code is involved. The current generation, the <a href="/wiki/PlayStation_5" title="PlayStation 5">PlayStation 5</a> and the <a href="/wiki/Xbox_Series_X_and_Series_S" title="Xbox Series X and Series S">Xbox Series X and Series S</a> respectively, also incorporate AMD x86-64 processors, based on the <a href="/wiki/Zen_2" title="Zen 2">Zen 2</a> microarchitecture.<a href="#cite_note-123">[118]</a><a href="#cite_note-124">[119]</a> Although considered a PC, the <a href="/wiki/Steam_Deck" title="Steam Deck">Steam Deck</a> uses a custom AMD x86-64 <a href="/wiki/AMD_Accelerated_Processing_Unit" class="mw-redirect" title="AMD Accelerated Processing Unit">accelerated processing unit</a> (APU), based on the Zen 2 microarchitecture.<a href="#cite_note-verge_tech_pres_details-125">[120]</a> <div class="mw-heading mw-heading2"><h2 id="Industry_naming_conventions">Industry naming conventions</h2>[<a href="/w/index.php?title=X86-64&action=edit&section=38" title="Edit section: Industry naming conventions">edit</a>]</div> Since AMD64 and Intel 64 are substantially similar, many software and hardware products use one vendor-neutral term to indicate their compatibility with both implementations. AMD's original designation for this processor architecture, "x86-64", is still used for this purpose,<a href="#cite_note-apple-x86-64-2">[2]</a> as is the variant "x86_64".<a href="#cite_note-apple-x86_64-arch-manpage-3">[3]</a><a href="#cite_note-apple-x86_64-email-4">[4]</a> Other companies, such as <a href="/wiki/Microsoft" title="Microsoft">Microsoft</a><a href="#cite_note-ms-x64-6">[6]</a> and <a href="/wiki/Sun_Microsystems" title="Sun Microsystems">Sun Microsystems</a>/<a href="/wiki/Oracle_Corporation" title="Oracle Corporation">Oracle Corporation</a>,<a href="#cite_note-solaris-x64-5">[5]</a> use the contraction "x64" in marketing material. The term <a href="/wiki/IA-64" title="IA-64">IA-64</a> refers to the <a href="/wiki/Itanium" title="Itanium">Itanium</a> processor, and should not be confused with x86-64, as it is a completely different instruction set. Many operating systems and products, especially those that introduced x86-64 support prior to Intel's entry into the market, use the term "AMD64" or "amd64" to refer to both AMD64 and Intel 64. <ul><li>amd64 <ul><li>Most <a href="/wiki/BSD" class="mw-redirect" title="BSD">BSD</a> systems such as <a href="/wiki/FreeBSD" title="FreeBSD">FreeBSD</a>, <a href="/wiki/MidnightBSD" title="MidnightBSD">MidnightBSD</a>, <a href="/wiki/NetBSD" title="NetBSD">NetBSD</a> and <a href="/wiki/OpenBSD" title="OpenBSD">OpenBSD</a> refer to both AMD64 and Intel 64 under the architecture name "amd64".</li> <li>Some <a href="/wiki/Linux_distribution" title="Linux distribution">Linux distributions</a> such as <a href="/wiki/Debian" title="Debian">Debian</a>, <a href="/wiki/Ubuntu_(operating_system)" class="mw-redirect" title="Ubuntu (operating system)">Ubuntu</a>, <a href="/wiki/Gentoo_Linux" title="Gentoo Linux">Gentoo Linux</a> refer to both AMD64 and Intel 64 under the architecture name "amd64".</li> <li><a href="/wiki/Microsoft_Windows" title="Microsoft Windows">Microsoft Windows</a>'s x64 versions use the AMD64 moniker internally to designate various components which use or are compatible with this architecture. For example, the <a href="/wiki/Environment_variable" title="Environment variable">environment variable</a> PROCESSOR_ARCHITECTURE is assigned the value "AMD64" as opposed to "x86" in 32-bit versions, and the system directory on a Windows x64 Edition installation CD-ROM is named "AMD64", in contrast to "i386" in 32-bit versions.<a href="#cite_note-126">[121]</a></li> <li>Sun's <a href="/wiki/Solaris_(operating_system)" class="mw-redirect" title="Solaris (operating system)">Solaris</a>'s isalist command identifies both AMD64- and Intel 64-based systems as "amd64".</li> <li><a href="/wiki/Java_Development_Kit" title="Java Development Kit">Java Development Kit</a> (JDK): the name "amd64" is used in directory names containing x86-64 files.</li></ul></li> <li>x86_64 <ul><li>The <a href="/wiki/Linux_kernel" title="Linux kernel">Linux kernel</a><a href="#cite_note-127">[122]</a> and the <a href="/wiki/GNU_Compiler_Collection" title="GNU Compiler Collection">GNU Compiler Collection</a> refers to 64-bit architecture as "x86_64".</li> <li>Some Linux distributions, such as <a href="/wiki/Fedora_(operating_system)" class="mw-redirect" title="Fedora (operating system)">Fedora</a>, <a href="/wiki/OpenSUSE" title="OpenSUSE">openSUSE</a>, <a href="/wiki/Arch_Linux" title="Arch Linux">Arch Linux</a>, <a href="/wiki/Gentoo_Linux" title="Gentoo Linux">Gentoo Linux</a> refer to this 64-bit architecture as "x86_64".</li> <li>Apple <a href="/wiki/MacOS" title="MacOS">macOS</a> refers to 64-bit architecture as "x86-64" or "x86_64", as seen in the Terminal command <code>arch</code><a href="#cite_note-apple-x86_64-arch-manpage-3">[3]</a> and in their developer documentation.<a href="#cite_note-apple-x86-64-2">[2]</a><a href="#cite_note-apple-x86_64-email-4">[4]</a></li> <li>Breaking with most other BSD systems, <a href="/wiki/DragonFly_BSD" title="DragonFly BSD">DragonFly BSD</a> refers to 64-bit architecture as "x86_64".</li> <li><a href="/wiki/Haiku_(operating_system)" title="Haiku (operating system)">Haiku</a> refers to 64-bit architecture as "x86_64".</li></ul></li></ul> <div class="mw-heading mw-heading2"><h2 id="Licensing">Licensing</h2>[<a href="/w/index.php?title=X86-64&action=edit&section=39" title="Edit section: Licensing">edit</a>]</div> x86-64/AMD64 was solely developed by AMD. Until April 2021 when the relevant patents expired, AMD held patents on techniques used in AMD64;<a href="#cite_note-128">[123]</a><a href="#cite_note-129">[124]</a><a href="#cite_note-130">[125]</a> those patents had to be licensed from AMD in order to implement AMD64. Intel entered into a cross-licensing agreement with AMD, licensing to AMD their patents on existing x86 techniques, and licensing from AMD their patents on techniques used in x86-64.<a href="#cite_note-131">[126]</a> In 2009, AMD and Intel settled several lawsuits and cross-licensing disagreements, extending their cross-licensing agreements.<a href="#cite_note-132">[127]</a><a href="#cite_note-133">[128]</a><a href="#cite_note-134">[129]</a> <div class="mw-heading mw-heading2"><h2 id="See_also">See also</h2>[<a href="/w/index.php?title=X86-64&action=edit&section=40" title="Edit section: See also">edit</a>]</div> <ul><li><a href="/wiki/AGESA" title="AGESA">AMD Generic Encapsulated Software Architecture</a> (AGESA)</li> <li><a href="/wiki/Speculative_execution_CPU_vulnerabilities" class="mw-redirect" title="Speculative execution CPU vulnerabilities">Speculative execution CPU vulnerabilities</a></li></ul> <div class="mw-heading mw-heading2"><h2 id="Notes">Notes</h2>[<a href="/w/index.php?title=X86-64&action=edit&section=41" title="Edit section: Notes">edit</a>]</div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1239543626"><div class="reflist"> <div class="mw-references-wrap"><ol class="references"> <li id="cite_note-11"><a href="#cite_ref-11">^</a> Various names are used for the instruction set. Prior to the launch, x86-64 and x86_64 were used, while upon the release AMD named it AMD64.<a href="#cite_note-inq-amd64-1">[1]</a> Intel initially used the names IA-32e and EM64T before finally settling on "Intel 64" for its implementation. Some in the industry, including <a href="/wiki/Apple_Inc." title="Apple Inc.">Apple</a>,<a href="#cite_note-apple-x86-64-2">[2]</a><a href="#cite_note-apple-x86_64-arch-manpage-3">[3]</a><a href="#cite_note-apple-x86_64-email-4">[4]</a> use x86-64 and x86_64, while others, notably <a href="/wiki/Sun_Microsystems" title="Sun Microsystems">Sun Microsystems</a><a href="#cite_note-solaris-x64-5">[5]</a> (now <a href="/wiki/Oracle_Corporation" title="Oracle Corporation">Oracle Corporation</a>) and <a href="/wiki/Microsoft" title="Microsoft">Microsoft</a>,<a href="#cite_note-ms-x64-6">[6]</a> use x64. The <a href="/wiki/BSD" class="mw-redirect" title="BSD">BSD</a> family of OSs and several <a href="/wiki/Linux_distribution" title="Linux distribution">Linux distributions</a><a href="#cite_note-7">[7]</a><a href="#cite_note-8">[8]</a> use AMD64, as does Microsoft Windows internally.<a href="#cite_note-9">[9]</a><a href="#cite_note-10">[10]</a> </li> <li id="cite_note-14"><a href="#cite_ref-14">^</a> In practice, 64-bit operating systems generally do not support 16-bit applications, although modern versions of Microsoft Windows contain a limited workaround that effectively supports 16-bit <a href="/wiki/InstallShield" title="InstallShield">InstallShield</a> and Microsoft ACME installers by silently substituting them with 32-bit code.<a href="#cite_note-13">[12]</a> </li> </ol></div></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1239543626"><div class="reflist reflist-lower-alpha"> <div class="mw-references-wrap"><ol class="references"> <li id="cite_note-72"><a href="#cite_ref-72">^</a> <a href="/wiki/The_Register" title="The Register">The Register</a> reported that the stepping G1 (0F49h) of Pentium 4 will sample on October 17 and ship in volume on November 14.<a href="#cite_note-70">[66]</a> However, Intel's document says that samples are available on September 9, whereas October 17 is the "date of first availability of post-conversion material", which Intel defines as "the projected date that a customer may expect to receive the post-conversion materials. ... customers should be prepared to receive the post-converted materials on this date".<a href="#cite_note-71">[67]</a> </li> </ol></div></div> <div class="mw-heading mw-heading2"><h2 id="References">References</h2>[<a href="/w/index.php?title=X86-64&action=edit&section=42" title="Edit section: References">edit</a>]</div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1239543626"><div class="reflist reflist-columns references-column-width" style="column-width: 30em;"> <ol class="references"> <li id="cite_note-inq-amd64-1"><a href="#cite_ref-inq-amd64_1-0">^</a> <style data-mw-deduplicate="TemplateStyles:r1238218222">.mw-parser-output cite.citation{font-style:inherit;word-wrap:break-word}.mw-parser-output .citation q{quotes:"\"""\"""'""'"}.mw-parser-output .citation:target{background-color:rgba(0,127,255,0.133)}.mw-parser-output .id-lock-free.id-lock-free a{background:url("//upload.wikimedia.org/wikipedia/commons/6/65/Lock-green.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-limited.id-lock-limited a,.mw-parser-output .id-lock-registration.id-lock-registration a{background:url("//upload.wikimedia.org/wikipedia/commons/d/d6/Lock-gray-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-subscription.id-lock-subscription a{background:url("//upload.wikimedia.org/wikipedia/commons/a/aa/Lock-red-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .cs1-ws-icon a{background:url("//upload.wikimedia.org/wikipedia/commons/4/4c/Wikisource-logo.svg")right 0.1em center/12px no-repeat}body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-free a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-limited a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-registration a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-subscription a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .cs1-ws-icon a{background-size:contain;padding:0 1em 0 0}.mw-parser-output .cs1-code{color:inherit;background:inherit;border:none;padding:inherit}.mw-parser-output .cs1-hidden-error{display:none;color:var(--color-error,#d33)}.mw-parser-output .cs1-visible-error{color:var(--color-error,#d33)}.mw-parser-output .cs1-maint{display:none;color:#085;margin-left:0.3em}.mw-parser-output .cs1-kern-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right{padding-right:0.2em}.mw-parser-output .citation .mw-selflink{font-weight:inherit}@media screen{.mw-parser-output .cs1-format{font-size:95%}html.skin-theme-clientpref-night .mw-parser-output .cs1-maint{color:#18911f}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .cs1-maint{color:#18911f}}</style><cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://wiki.debian.org/DebianAMD64Faq">"Debian AMD64 FAQ"</a>. Debian Wiki. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20190926163758/https://wiki.debian.org/DebianAMD64Faq">Archived</a> from the original on September 26, 2019. Retrieved May 3, 2012.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=Debian+Wiki&rft.atitle=Debian+AMD64+FAQ&rft_id=http%3A%2F%2Fwiki.debian.org%2FDebianAMD64Faq&rfr_id=info%3Asid%2Fen.wikipedia.org%3AX86-64" class="Z3988"> </li> <li id="cite_note-apple-x86-64-2">^ <a href="#cite_ref-apple-x86-64_2-0">a</a> <a href="#cite_ref-apple-x86-64_2-1">b</a> <a href="#cite_ref-apple-x86-64_2-2">c</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://developer.apple.com/library/mac/#documentation/developertools/Conceptual/MachOTopics/1-Articles/x86_64_code.html">"x86-64 Code Model"</a>. Apple. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20120602013413/https://developer.apple.com/library/mac/#documentation/developertools/Conceptual/MachOTopics/1-Articles/x86_64_code.html">Archived</a> from the original on June 2, 2012. Retrieved November 23, 2012.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=x86-64+Code+Model&rft.pub=Apple&rft_id=https%3A%2F%2Fdeveloper.apple.com%2Flibrary%2Fmac%2F%23documentation%2Fdevelopertools%2FConceptual%2FMachOTopics%2F1-Articles%2Fx86_64_code.html&rfr_id=info%3Asid%2Fen.wikipedia.org%3AX86-64" class="Z3988"> </li> <li id="cite_note-apple-x86_64-arch-manpage-3">^ <a href="#cite_ref-apple-x86_64-arch-manpage_3-0">a</a> <a href="#cite_ref-apple-x86_64-arch-manpage_3-1">b</a> <a href="#cite_ref-apple-x86_64-arch-manpage_3-2">c</a> <code><a rel="nofollow" class="external text" href="https://keith.github.io/xcode-man-pages/arch.1.html">arch(1)</a></code> – <a href="/wiki/Darwin_(operating_system)" title="Darwin (operating system)">Darwin</a> and <a href="/wiki/MacOS" title="MacOS">macOS</a> General Commands <a href="/wiki/Man_page" title="Man page">Manual</a> </li> <li id="cite_note-apple-x86_64-email-4">^ <a href="#cite_ref-apple-x86_64-email_4-0">a</a> <a href="#cite_ref-apple-x86_64-email_4-1">b</a> <a href="#cite_ref-apple-x86_64-email_4-2">c</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFKevin_Van_Vechten2006" class="citation web cs1">Kevin Van Vechten (August 9, 2006). <a rel="nofollow" class="external text" href="https://web.archive.org/web/20200201090447/https://lists.apple.com/archives/Darwin-dev/2006/Aug/msg00095.html">"re: Intel XNU bug report"</a>. Darwin-dev mailing list. <a href="/wiki/Apple_Computer" class="mw-redirect" title="Apple Computer">Apple Computer</a>. Archived from <a rel="nofollow" class="external text" href="http://lists.apple.com/archives/Darwin-dev/2006/Aug/msg00095.html">the original</a> on February 1, 2020. Retrieved October 5, 2006. <q>The kernel and developer tools have standardized on "x86_64" for the name of the Mach-O architecture</q></cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=Darwin-dev+mailing+list&rft.atitle=re%3A+Intel+XNU+bug+report&rft.date=2006-08-09&rft.au=Kevin+Van+Vechten&rft_id=http%3A%2F%2Flists.apple.com%2Farchives%2FDarwin-dev%2F2006%2FAug%2Fmsg00095.html&rfr_id=info%3Asid%2Fen.wikipedia.org%3AX86-64" class="Z3988"> </li> <li id="cite_note-solaris-x64-5">^ <a href="#cite_ref-solaris-x64_5-0">a</a> <a href="#cite_ref-solaris-x64_5-1">b</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://www.oracle.com/technetwork/server-storage/solaris/overview/solaris10amdopteron-jsp-140575.html">"Solaris 10 on AMD Opteron"</a>. Oracle. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20170725114435/http://www.oracle.com/technetwork/server-storage/solaris/overview/solaris10amdopteron-jsp-140575.html">Archived</a> from the original on July 25, 2017. Retrieved December 9, 2010.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=Solaris+10+on+AMD+Opteron&rft.pub=Oracle&rft_id=http%3A%2F%2Fwww.oracle.com%2Ftechnetwork%2Fserver-storage%2Fsolaris%2Foverview%2Fsolaris10amdopteron-jsp-140575.html&rfr_id=info%3Asid%2Fen.wikipedia.org%3AX86-64" class="Z3988"> </li> <li id="cite_note-ms-x64-6">^ <a href="#cite_ref-ms-x64_6-0">a</a> <a href="#cite_ref-ms-x64_6-1">b</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://web.archive.org/web/20101212040212/http://www.microsoft.com/windowsserver2008/en/us/64bit-computing.aspx">"Microsoft 64-Bit Computing"</a>. Microsoft. Archived from <a rel="nofollow" class="external text" href="http://www.microsoft.com/windowsserver2008/en/us/64bit-computing.aspx">the original</a> on December 12, 2010. Retrieved December 9, 2010.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=Microsoft+64-Bit+Computing&rft.pub=Microsoft&rft_id=http%3A%2F%2Fwww.microsoft.com%2Fwindowsserver2008%2Fen%2Fus%2F64bit-computing.aspx&rfr_id=info%3Asid%2Fen.wikipedia.org%3AX86-64" class="Z3988"> </li> <li id="cite_note-7"><a href="#cite_ref-7">^</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://www.debian.org/ports/amd64/">"AMD64 Port"</a>. Debian. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20190926060654/https://www.debian.org/ports/amd64/">Archived</a> from the original on September 26, 2019. 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Retrieved May 27, 2013.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=Gentoo%2FAMD64+Project&rft.pub=Gentoo+Project&rft_id=http%3A%2F%2Fwww.gentoo.org%2Fproj%2Fen%2Fbase%2Famd64%2F&rfr_id=info%3Asid%2Fen.wikipedia.org%3AX86-64" class="Z3988"> </li> <li id="cite_note-9"><a href="#cite_ref-9">^</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://msdn.microsoft.com/en-us/library/windows/desktop/aa384274(v=vs.85).aspx">"WOW64 Implementation Details"</a>. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20180413001932/https://msdn.microsoft.com/en-us/library/windows/desktop/aa384274(v=vs.85).aspx">Archived</a> from the original on April 13, 2018. Retrieved January 24, 2016.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=WOW64+Implementation+Details&rft_id=https%3A%2F%2Fmsdn.microsoft.com%2Fen-us%2Flibrary%2Fwindows%2Fdesktop%2Faa384274%28v%3Dvs.85%29.aspx&rfr_id=info%3Asid%2Fen.wikipedia.org%3AX86-64" class="Z3988"> </li> <li id="cite_note-10"><a href="#cite_ref-10">^</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://msdn.microsoft.com/en-us/library/microsoft.build.utilities.processorarchitecture.aspx">"ProcessorArchitecture Class"</a>. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20170603232543/https://msdn.microsoft.com/en-us/library/microsoft.build.utilities.processorarchitecture.aspx">Archived</a> from the original on June 3, 2017. 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Retrieved March 25, 2017.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=AMD64+Architecture+Programmer%27s+Manual&rft.atitle=Volume+2%3A+System+Programming&rft.date=2016-12&rft.au=AMD+Corporation&rft_id=http%3A%2F%2Fsupport.amd.com%2FTechDocs%2F24593.pdf&rfr_id=info%3Asid%2Fen.wikipedia.org%3AX86-64" class="Z3988"> </li> <li id="cite_note-13"><a href="#cite_ref-13">^</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFRaymond_Chen2013" class="citation web cs1">Raymond Chen (October 31, 2013). <a rel="nofollow" class="external text" href="https://devblogs.microsoft.com/oldnewthing/20131031-00/?p=2783">"If there is no 16-bit emulation layer in 64-bit Windows, how come certain 16-bit installers are allowed to run?"</a>. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20210714084610/https://devblogs.microsoft.com/oldnewthing/20131031-00/?p=2783">Archived</a> from the original on July 14, 2021. 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September 6, 2007. p. 14. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20220125121650/ftp://ftp.software.ibm.com/software/webserver/appserv/was/64bitPerf.pdf">Archived</a> (PDF) from the original on January 25, 2022. Retrieved April 9, 2010. <q>Figures 5, 6 and 7 also show the 32-bit version of WAS runs applications at full native hardware performance on the POWER and x86-64 platforms. Unlike some 64-bit processor architectures, the POWER and x86-64 hardware does not emulate 32-bit mode. 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Retrieved February 27, 2016. <q>Physical address space increased to 48 bits.</q></cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=BIOS+and+Kernel+Developer%27s+Guide+%28BKDG%29+For+AMD+Family+10h+Processors&rft.pages=24&rft_id=http%3A%2F%2Fdeveloper.amd.com%2Fwordpress%2Fmedia%2F2012%2F10%2F31116.pdf&rfr_id=info%3Asid%2Fen.wikipedia.org%3AX86-64" class="Z3988"> </li> <li id="cite_note-22"><a href="#cite_ref-22">^</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://web.archive.org/web/20101010233951/http://www.amd64.org/fileadmin/user_upload/pub/64bit_Linux-Myths_and_Facts.pdf">"Myth and facts about 64-bit Linux"</a> (PDF). March 2, 2008. p. 7. 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Retrieved April 27, 2014. <q>To install a 64-bit OS on a 64-bit PC, your processor needs to support CMPXCHG16b, PrefetchW, and LAHF/SAHF.</q></cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=System+Requirements%E2%80%94Windows+8.1&rft_id=http%3A%2F%2Fwindows.microsoft.com%2Fen-us%2Fwindows-8%2Fsystem-requirements&rfr_id=info%3Asid%2Fen.wikipedia.org%3AX86-64" class="Z3988"> </li> <li id="cite_note-65"><a href="#cite_ref-65">^</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFPetkov2009" class="citation web cs1">Petkov, Borislav (August 10, 2009). <a rel="nofollow" class="external text" href="https://lkml.org/lkml/2009/8/10/159">"Re: [PATCH v2] x86: clear incorrectly forced X86_FEATURE_LAHF_LM flag"</a>. <a href="/wiki/Linux_kernel_mailing_list" title="Linux kernel mailing list">Linux kernel mailing list</a>. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20230111050420/https://lkml.org/lkml/2009/8/10/159">Archived</a> from the original on January 11, 2023. 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Retrieved June 30, 2022.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=The+Register&rft.atitle=Intel+tweaks+EM64T+for+full+AMD64+compatibility&rft.date=2005-08-23&rft.aulast=Smith&rft.aufirst=Tony&rft_id=https%3A%2F%2Fwww.theregister.com%2F2005%2F08%2F23%2Fintel_fixes_em64t%2F&rfr_id=info%3Asid%2Fen.wikipedia.org%3AX86-64" class="Z3988"> </li> <li id="cite_note-71"><a href="#cite_ref-71">^</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://web.archive.org/web/20051117162258/http://developer.intel.com/design/pcn/Processors/D0105271.pdf">"Product Change Notification 105271 – 00"</a> (PDF). Intel. 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Intel. 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Archived from <a rel="nofollow" class="external text" href="http://www.anandtech.com/show/2873">the original</a> on May 13, 2010.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=AnandTech&rft.atitle=AMD+and+Intel+Settle+Their+Differences%3A+AMD+Gets+To+Go+Fabless&rft.date=2009-11-12&rft.aulast=Smith&rft.aufirst=Ryan&rft_id=http%3A%2F%2Fwww.anandtech.com%2Fshow%2F2873&rfr_id=info%3Asid%2Fen.wikipedia.org%3AX86-64" class="Z3988"> </li> </ol></div> <div class="mw-heading mw-heading2"><h2 id="External_links">External links</h2>[<a href="/w/index.php?title=X86-64&action=edit&section=43" title="Edit section: External links">edit</a>]</div> <ul><li><a rel="nofollow" class="external text" href="https://developer.amd.com/resources/developer-guides-manuals/">AMD Developer Guides, Manuals & ISA Documents</a></li> <li><a rel="nofollow" class="external text" href="http://www.stanford.edu/class/ee380/Abstracts/O00927.html">x86-64: Extending the x86 architecture to 64-bits</a> – technical talk by the architect of AMD64 (<a rel="nofollow" class="external text" href="https://web.archive.org/web/20100813052749/http://stanford-online.stanford.edu/courses/ee380/000927-ee380-100.asx">video archive</a>), and <a rel="nofollow" class="external text" href="http://www.stanford.edu/class/ee380/Abstracts/040107.html">second talk by the same speaker</a> (<a rel="nofollow" class="external text" href="https://web.archive.org/web/20100813100133/http://stanford-online.stanford.edu/courses/ee380/040107-ee380-100.asx">video archive</a>)</li> <li><a rel="nofollow" class="external text" href="https://web.archive.org/web/20060623073619/http://www.xbitlabs.com/news/other/display/20041227094638.html">AMD's "Enhanced Virus Protection"</a></li> <li><a rel="nofollow" class="external text" href="https://www.theregister.co.uk/2005/08/23/intel_fixes_em64t/">Intel tweaks EM64T for full AMD64 compatibility</a></li> <li><a rel="nofollow" class="external text" href="http://www.extremetech.com/extreme/56018-analyst-intel-reverseengineered-amd64">Analyst: Intel Reverse-Engineered AMD64</a></li> <li><a rel="nofollow" class="external text" href="https://marc.info/?l=linux-kernel&m=107766481408468&w=2">Early report of differences between Intel IA32e and AMD64</a></li> <li><a rel="nofollow" class="external text" href="http://gcc.gnu.org/pub/gcc/summit/2003/Porting%20to%2064%20bit.pdf">Porting to 64-bit GNU/Linux Systems</a>, by Andreas Jaeger from <a href="/wiki/GCC_Summit" title="GCC Summit">GCC Summit</a> 2003. An excellent paper explaining almost all practical aspects for a transition from 32-bit to 64-bit.</li> <li><a rel="nofollow" class="external text" href="http://www.intel.com/technology/intel64/index.htm">Intel 64 Architecture</a></li> <li><a rel="nofollow" class="external text" href="https://web.archive.org/web/20110403005033/http://software.intel.com/en-us/articles/all-about-64-bits/">Intel Software Network: "64 bits"</a></li> <li><a rel="nofollow" class="external text" href="https://web.archive.org/web/20170222181811/http://www.turboirc.com/asm/">TurboIRC.COM tutorials, including examples of how to of enter protected and long mode the raw way from DOS</a></li> <li><a rel="nofollow" class="external text" href="https://web.archive.org/web/20100123010204/http://software.intel.com/en-us/articles/seven-steps-of-migrating-a-program-to-a-64-bit-system/">Seven Steps of Migrating a Program to a 64-bit System</a></li> <li><a rel="nofollow" class="external text" href="http://msdn.microsoft.com/en-us/library/aa366778%28VS.85%29.aspx">Memory Limits for Windows Releases</a></li></ul> <div class="navbox-styles"><style data-mw-deduplicate="TemplateStyles:r1129693374">.mw-parser-output .hlist dl,.mw-parser-output .hlist ol,.mw-parser-output .hlist ul{margin:0;padding:0}.mw-parser-output .hlist dd,.mw-parser-output .hlist dt,.mw-parser-output .hlist li{margin:0;display:inline}.mw-parser-output .hlist.inline,.mw-parser-output .hlist.inline dl,.mw-parser-output .hlist.inline ol,.mw-parser-output .hlist.inline ul,.mw-parser-output .hlist dl dl,.mw-parser-output .hlist dl ol,.mw-parser-output .hlist dl ul,.mw-parser-output .hlist ol dl,.mw-parser-output .hlist ol ol,.mw-parser-output .hlist ol ul,.mw-parser-output .hlist ul dl,.mw-parser-output .hlist ul ol,.mw-parser-output .hlist ul ul{display:inline}.mw-parser-output .hlist .mw-empty-li{display:none}.mw-parser-output .hlist dt::after{content:": "}.mw-parser-output .hlist dd::after,.mw-parser-output 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