CINXE.COM

<!DOCTYPE html> <html class="client-nojs vector-feature-language-in-header-enabled vector-feature-language-in-main-page-header-disabled vector-feature-sticky-header-disabled vector-feature-page-tools-pinned-disabled vector-feature-toc-pinned-clientpref-1 vector-feature-main-menu-pinned-disabled vector-feature-limited-width-clientpref-1 vector-feature-limited-width-content-enabled vector-feature-custom-font-size-clientpref-1 vector-feature-appearance-pinned-clientpref-1 vector-feature-night-mode-enabled skin-theme-clientpref-day vector-toc-available" lang="en" dir="ltr"> <head> <meta charset="UTF-8"> <title>Copy-on-write - Wikipedia</title> <script>(function(){var className="client-js vector-feature-language-in-header-enabled vector-feature-language-in-main-page-header-disabled vector-feature-sticky-header-disabled vector-feature-page-tools-pinned-disabled vector-feature-toc-pinned-clientpref-1 vector-feature-main-menu-pinned-disabled vector-feature-limited-width-clientpref-1 vector-feature-limited-width-content-enabled vector-feature-custom-font-size-clientpref-1 vector-feature-appearance-pinned-clientpref-1 vector-feature-night-mode-enabled skin-theme-clientpref-day vector-toc-available";var cookie=document.cookie.match(/(?:^|; )enwikimwclientpreferences=([^;]+)/);if(cookie){cookie[1].split('%2C').forEach(function(pref){className=className.replace(new RegExp('(^| )'+pref.replace(/-clientpref-\w+$|[^\w-]+/g,'')+'-clientpref-\\w+( |$)'),'$1'+pref+'$2');});}document.documentElement.className=className;}());RLCONF={"wgBreakFrames":false,"wgSeparatorTransformTable":["",""],"wgDigitTransformTable":["",""],"wgDefaultDateFormat":"dmy", "wgMonthNames":["","January","February","March","April","May","June","July","August","September","October","November","December"],"wgRequestId":"afd399e1-f8b2-434b-b417-260bc9246383","wgCanonicalNamespace":"","wgCanonicalSpecialPageName":false,"wgNamespaceNumber":0,"wgPageName":"Copy-on-write","wgTitle":"Copy-on-write","wgCurRevisionId":1258225312,"wgRevisionId":1258225312,"wgArticleId":407603,"wgIsArticle":true,"wgIsRedirect":false,"wgAction":"view","wgUserName":null,"wgUserGroups":["*"],"wgCategories":["CS1 maint: unfit URL","Articles with short description","Short description is different from Wikidata","Use dmy dates from November 2023","All articles with unsourced statements","Articles with unsourced statements from November 2023","Articles to be expanded from October 2017","All articles to be expanded","Articles with example C++ code","Computer data storage","Software optimization","Virtual memory","Virtualization"],"wgPageViewLanguage":"en","wgPageContentLanguage":"en", "wgPageContentModel":"wikitext","wgRelevantPageName":"Copy-on-write","wgRelevantArticleId":407603,"wgIsProbablyEditable":true,"wgRelevantPageIsProbablyEditable":true,"wgRestrictionEdit":[],"wgRestrictionMove":[],"wgNoticeProject":"wikipedia","wgCiteReferencePreviewsActive":false,"wgFlaggedRevsParams":{"tags":{"status":{"levels":1}}},"wgMediaViewerOnClick":true,"wgMediaViewerEnabledByDefault":true,"wgPopupsFlags":0,"wgVisualEditor":{"pageLanguageCode":"en","pageLanguageDir":"ltr","pageVariantFallbacks":"en"},"wgMFDisplayWikibaseDescriptions":{"search":true,"watchlist":true,"tagline":false,"nearby":true},"wgWMESchemaEditAttemptStepOversample":false,"wgWMEPageLength":10000,"wgRelatedArticlesCompat":[],"wgCentralAuthMobileDomain":false,"wgEditSubmitButtonLabelPublish":true,"wgULSPosition":"interlanguage","wgULSisCompactLinksEnabled":false,"wgVector2022LanguageInHeader":true,"wgULSisLanguageSelectorEmpty":false,"wgWikibaseItemId":"Q1131607","wgCheckUserClientHintsHeadersJsApi":["brands", "architecture","bitness","fullVersionList","mobile","model","platform","platformVersion"],"GEHomepageSuggestedEditsEnableTopics":true,"wgGETopicsMatchModeEnabled":false,"wgGEStructuredTaskRejectionReasonTextInputEnabled":false,"wgGELevelingUpEnabledForUser":false};RLSTATE={"ext.globalCssJs.user.styles":"ready","site.styles":"ready","user.styles":"ready","ext.globalCssJs.user":"ready","user":"ready","user.options":"loading","ext.cite.styles":"ready","ext.pygments":"ready","skins.vector.search.codex.styles":"ready","skins.vector.styles":"ready","skins.vector.icons":"ready","jquery.makeCollapsible.styles":"ready","ext.wikimediamessages.styles":"ready","ext.visualEditor.desktopArticleTarget.noscript":"ready","ext.uls.interlanguage":"ready","wikibase.client.init":"ready","ext.wikimediaBadges":"ready"};RLPAGEMODULES=["ext.cite.ux-enhancements","ext.pygments.view","site","mediawiki.page.ready","jquery.makeCollapsible","mediawiki.toc","skins.vector.js","ext.centralNotice.geoIP", "ext.centralNotice.startUp","ext.gadget.ReferenceTooltips","ext.gadget.switcher","ext.urlShortener.toolbar","ext.centralauth.centralautologin","mmv.bootstrap","ext.popups","ext.visualEditor.desktopArticleTarget.init","ext.visualEditor.targetLoader","ext.echo.centralauth","ext.eventLogging","ext.wikimediaEvents","ext.navigationTiming","ext.uls.interface","ext.cx.eventlogging.campaigns","ext.cx.uls.quick.actions","wikibase.client.vector-2022","ext.checkUser.clientHints","ext.growthExperiments.SuggestedEditSession","wikibase.sidebar.tracking"];</script> <script>(RLQ=window.RLQ||[]).push(function(){mw.loader.impl(function(){return["user.options@12s5i",function($,jQuery,require,module){mw.user.tokens.set({"patrolToken":"+\\","watchToken":"+\\","csrfToken":"+\\"}); }];});});</script> <link rel="stylesheet" href="/w/load.php?lang=en&modules=ext.cite.styles%7Cext.pygments%2CwikimediaBadges%7Cext.uls.interlanguage%7Cext.visualEditor.desktopArticleTarget.noscript%7Cext.wikimediamessages.styles%7Cjquery.makeCollapsible.styles%7Cskins.vector.icons%2Cstyles%7Cskins.vector.search.codex.styles%7Cwikibase.client.init&only=styles&skin=vector-2022"> <script async="" src="/w/load.php?lang=en&modules=startup&only=scripts&raw=1&skin=vector-2022"></script> <meta name="ResourceLoaderDynamicStyles" content=""> <link rel="stylesheet" href="/w/load.php?lang=en&modules=site.styles&only=styles&skin=vector-2022"> <meta name="generator" content="MediaWiki 1.44.0-wmf.4"> <meta name="referrer" content="origin"> <meta name="referrer" content="origin-when-cross-origin"> <meta name="robots" content="max-image-preview:standard"> <meta name="format-detection" content="telephone=no"> <meta name="viewport" content="width=1120"> <meta property="og:title" content="Copy-on-write - Wikipedia"> <meta property="og:type" content="website"> <link rel="preconnect" href="//upload.wikimedia.org"> <link rel="alternate" media="only screen and (max-width: 640px)" href="//en.m.wikipedia.org/wiki/Copy-on-write"> <link rel="alternate" type="application/x-wiki" title="Edit this page" href="/w/index.php?title=Copy-on-write&action=edit"> <link rel="apple-touch-icon" href="/static/apple-touch/wikipedia.png"> <link rel="icon" href="/static/favicon/wikipedia.ico"> <link rel="search" type="application/opensearchdescription+xml" href="/w/rest.php/v1/search" title="Wikipedia (en)"> <link rel="EditURI" type="application/rsd+xml" href="//en.wikipedia.org/w/api.php?action=rsd"> <link rel="canonical" href="https://en.wikipedia.org/wiki/Copy-on-write"> <link rel="license" href="https://creativecommons.org/licenses/by-sa/4.0/deed.en"> <link rel="alternate" type="application/atom+xml" title="Wikipedia Atom feed" href="/w/index.php?title=Special:RecentChanges&feed=atom"> <link rel="dns-prefetch" href="//meta.wikimedia.org" /> <link rel="dns-prefetch" href="//login.wikimedia.org"> </head> <body class="skin--responsive skin-vector skin-vector-search-vue mediawiki ltr sitedir-ltr mw-hide-empty-elt ns-0 ns-subject mw-editable page-Copy-on-write rootpage-Copy-on-write skin-vector-2022 action-view"><a class="mw-jump-link" href="#bodyContent">Jump to content</a> <div class="vector-header-container"> <header class="vector-header mw-header"> <div class="vector-header-start"> <nav class="vector-main-menu-landmark" aria-label="Site"> <div id="vector-main-menu-dropdown" class="vector-dropdown vector-main-menu-dropdown vector-button-flush-left vector-button-flush-right" > <input type="checkbox" id="vector-main-menu-dropdown-checkbox" role="button" aria-haspopup="true" data-event-name="ui.dropdown-vector-main-menu-dropdown" class="vector-dropdown-checkbox " aria-label="Main menu" > <label id="vector-main-menu-dropdown-label" for="vector-main-menu-dropdown-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" ><span class="vector-icon mw-ui-icon-menu mw-ui-icon-wikimedia-menu"></span> <span class="vector-dropdown-label-text">Main menu</span> </label> <div class="vector-dropdown-content"> <div id="vector-main-menu-unpinned-container" class="vector-unpinned-container"> <div id="vector-main-menu" class="vector-main-menu vector-pinnable-element"> <div class="vector-pinnable-header vector-main-menu-pinnable-header vector-pinnable-header-unpinned" data-feature-name="main-menu-pinned" data-pinnable-element-id="vector-main-menu" data-pinned-container-id="vector-main-menu-pinned-container" data-unpinned-container-id="vector-main-menu-unpinned-container" > <div class="vector-pinnable-header-label">Main menu</div> <button class="vector-pinnable-header-toggle-button vector-pinnable-header-pin-button" data-event-name="pinnable-header.vector-main-menu.pin">move to sidebar</button> <button class="vector-pinnable-header-toggle-button vector-pinnable-header-unpin-button" data-event-name="pinnable-header.vector-main-menu.unpin">hide</button> </div> <div id="p-navigation" class="vector-menu mw-portlet mw-portlet-navigation" > <div class="vector-menu-heading"> Navigation </div> <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li id="n-mainpage-description" class="mw-list-item"><a href="/wiki/Main_Page" title="Visit the main page [z]" accesskey="z"><span>Main page</span></a></li><li id="n-contents" class="mw-list-item"><a href="/wiki/Wikipedia:Contents" title="Guides to browsing Wikipedia"><span>Contents</span></a></li><li id="n-currentevents" class="mw-list-item"><a href="/wiki/Portal:Current_events" title="Articles related to current events"><span>Current events</span></a></li><li id="n-randompage" class="mw-list-item"><a href="/wiki/Special:Random" title="Visit a randomly selected article [x]" accesskey="x"><span>Random article</span></a></li><li id="n-aboutsite" class="mw-list-item"><a href="/wiki/Wikipedia:About" title="Learn about Wikipedia and how it works"><span>About Wikipedia</span></a></li><li id="n-contactpage" class="mw-list-item"><a href="//en.wikipedia.org/wiki/Wikipedia:Contact_us" title="How to contact Wikipedia"><span>Contact us</span></a></li> </ul> </div> </div> <div id="p-interaction" class="vector-menu mw-portlet mw-portlet-interaction" > <div class="vector-menu-heading"> Contribute </div> <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li id="n-help" class="mw-list-item"><a href="/wiki/Help:Contents" title="Guidance on how to use and edit Wikipedia"><span>Help</span></a></li><li id="n-introduction" class="mw-list-item"><a href="/wiki/Help:Introduction" title="Learn how to edit Wikipedia"><span>Learn to edit</span></a></li><li id="n-portal" class="mw-list-item"><a href="/wiki/Wikipedia:Community_portal" title="The hub for editors"><span>Community portal</span></a></li><li id="n-recentchanges" class="mw-list-item"><a href="/wiki/Special:RecentChanges" title="A list of recent changes to Wikipedia [r]" accesskey="r"><span>Recent changes</span></a></li><li id="n-upload" class="mw-list-item"><a href="/wiki/Wikipedia:File_upload_wizard" title="Add images or other media for use on Wikipedia"><span>Upload file</span></a></li> </ul> </div> </div> </div> </div> </div> </div> </nav> <a href="/wiki/Main_Page" class="mw-logo"> <img class="mw-logo-icon" src="/static/images/icons/wikipedia.png" alt="" aria-hidden="true" height="50" width="50"> <span class="mw-logo-container skin-invert"> <img class="mw-logo-wordmark" alt="Wikipedia" src="/static/images/mobile/copyright/wikipedia-wordmark-en.svg" style="width: 7.5em; height: 1.125em;"> <img class="mw-logo-tagline" alt="The Free Encyclopedia" src="/static/images/mobile/copyright/wikipedia-tagline-en.svg" width="117" height="13" style="width: 7.3125em; height: 0.8125em;"> </span> </a> </div> <div class="vector-header-end"> <div id="p-search" role="search" class="vector-search-box-vue vector-search-box-collapses vector-search-box-show-thumbnail vector-search-box-auto-expand-width vector-search-box"> <a href="/wiki/Special:Search" class="cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet cdx-button--icon-only search-toggle" title="Search Wikipedia [f]" accesskey="f"><span class="vector-icon mw-ui-icon-search mw-ui-icon-wikimedia-search"></span> <span>Search</span> </a> <div class="vector-typeahead-search-container"> <div class="cdx-typeahead-search cdx-typeahead-search--show-thumbnail cdx-typeahead-search--auto-expand-width"> <form action="/w/index.php" id="searchform" class="cdx-search-input cdx-search-input--has-end-button"> <div id="simpleSearch" class="cdx-search-input__input-wrapper" data-search-loc="header-moved"> <div class="cdx-text-input cdx-text-input--has-start-icon"> <input class="cdx-text-input__input" type="search" name="search" placeholder="Search Wikipedia" aria-label="Search Wikipedia" autocapitalize="sentences" title="Search Wikipedia [f]" accesskey="f" id="searchInput" > <span class="cdx-text-input__icon cdx-text-input__start-icon"></span> </div> <input type="hidden" name="title" value="Special:Search"> </div> <button class="cdx-button cdx-search-input__end-button">Search</button> </form> </div> </div> </div> <nav class="vector-user-links vector-user-links-wide" aria-label="Personal tools"> <div class="vector-user-links-main"> <div id="p-vector-user-menu-preferences" class="vector-menu mw-portlet emptyPortlet" > <div class="vector-menu-content"> <ul class="vector-menu-content-list"> </ul> </div> </div> <div id="p-vector-user-menu-userpage" class="vector-menu mw-portlet emptyPortlet" > <div class="vector-menu-content"> <ul class="vector-menu-content-list"> </ul> </div> </div> <nav class="vector-appearance-landmark" aria-label="Appearance"> <div id="vector-appearance-dropdown" class="vector-dropdown " title="Change the appearance of the page's font size, width, and color" > <input type="checkbox" id="vector-appearance-dropdown-checkbox" role="button" aria-haspopup="true" data-event-name="ui.dropdown-vector-appearance-dropdown" class="vector-dropdown-checkbox " aria-label="Appearance" > <label id="vector-appearance-dropdown-label" for="vector-appearance-dropdown-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" ><span class="vector-icon mw-ui-icon-appearance mw-ui-icon-wikimedia-appearance"></span> <span class="vector-dropdown-label-text">Appearance</span> </label> <div class="vector-dropdown-content"> <div id="vector-appearance-unpinned-container" class="vector-unpinned-container"> </div> </div> </div> </nav> <div id="p-vector-user-menu-notifications" class="vector-menu mw-portlet emptyPortlet" > <div class="vector-menu-content"> <ul class="vector-menu-content-list"> </ul> </div> </div> <div id="p-vector-user-menu-overflow" class="vector-menu mw-portlet" > <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li id="pt-sitesupport-2" class="user-links-collapsible-item mw-list-item user-links-collapsible-item"><a data-mw="interface" href="https://donate.wikimedia.org/wiki/Special:FundraiserRedirector?utm_source=donate&utm_medium=sidebar&utm_campaign=C13_en.wikipedia.org&uselang=en" class=""><span>Donate</span></a> </li> <li id="pt-createaccount-2" class="user-links-collapsible-item mw-list-item user-links-collapsible-item"><a data-mw="interface" href="/w/index.php?title=Special:CreateAccount&returnto=Copy-on-write" title="You are encouraged to create an account and log in; however, it is not mandatory" class=""><span>Create account</span></a> </li> <li id="pt-login-2" class="user-links-collapsible-item mw-list-item user-links-collapsible-item"><a data-mw="interface" href="/w/index.php?title=Special:UserLogin&returnto=Copy-on-write" title="You're encouraged to log in; however, it's not mandatory. [o]" accesskey="o" class=""><span>Log in</span></a> </li> </ul> </div> </div> </div> <div id="vector-user-links-dropdown" class="vector-dropdown vector-user-menu vector-button-flush-right vector-user-menu-logged-out" title="Log in and more options" > <input type="checkbox" id="vector-user-links-dropdown-checkbox" role="button" aria-haspopup="true" data-event-name="ui.dropdown-vector-user-links-dropdown" class="vector-dropdown-checkbox " aria-label="Personal tools" > <label id="vector-user-links-dropdown-label" for="vector-user-links-dropdown-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" ><span class="vector-icon mw-ui-icon-ellipsis mw-ui-icon-wikimedia-ellipsis"></span> <span class="vector-dropdown-label-text">Personal tools</span> </label> <div class="vector-dropdown-content"> <div id="p-personal" class="vector-menu mw-portlet mw-portlet-personal user-links-collapsible-item" title="User menu" > <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li id="pt-sitesupport" class="user-links-collapsible-item mw-list-item"><a href="https://donate.wikimedia.org/wiki/Special:FundraiserRedirector?utm_source=donate&utm_medium=sidebar&utm_campaign=C13_en.wikipedia.org&uselang=en"><span>Donate</span></a></li><li id="pt-createaccount" class="user-links-collapsible-item mw-list-item"><a href="/w/index.php?title=Special:CreateAccount&returnto=Copy-on-write" title="You are encouraged to create an account and log in; however, it is not mandatory"><span class="vector-icon mw-ui-icon-userAdd mw-ui-icon-wikimedia-userAdd"></span> <span>Create account</span></a></li><li id="pt-login" class="user-links-collapsible-item mw-list-item"><a href="/w/index.php?title=Special:UserLogin&returnto=Copy-on-write" title="You're encouraged to log in; however, it's not mandatory. [o]" accesskey="o"><span class="vector-icon mw-ui-icon-logIn mw-ui-icon-wikimedia-logIn"></span> <span>Log in</span></a></li> </ul> </div> </div> <div id="p-user-menu-anon-editor" class="vector-menu mw-portlet mw-portlet-user-menu-anon-editor" > <div class="vector-menu-heading"> Pages for logged out editors <a href="/wiki/Help:Introduction" aria-label="Learn more about editing"><span>learn more</span></a> </div> <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li id="pt-anoncontribs" class="mw-list-item"><a href="/wiki/Special:MyContributions" title="A list of edits made from this IP address [y]" accesskey="y"><span>Contributions</span></a></li><li id="pt-anontalk" class="mw-list-item"><a href="/wiki/Special:MyTalk" title="Discussion about edits from this IP address [n]" accesskey="n"><span>Talk</span></a></li> </ul> </div> </div> </div> </div> </nav> </div> </header> </div> <div class="mw-page-container"> <div class="mw-page-container-inner"> <div class="vector-sitenotice-container"> <div id="siteNotice"></div> </div> <div class="vector-column-start"> <div class="vector-main-menu-container"> <div id="mw-navigation"> <nav id="mw-panel" class="vector-main-menu-landmark" aria-label="Site"> <div id="vector-main-menu-pinned-container" class="vector-pinned-container"> </div> </nav> </div> </div> <div class="vector-sticky-pinned-container"> <nav id="mw-panel-toc" aria-label="Contents" data-event-name="ui.sidebar-toc" class="mw-table-of-contents-container vector-toc-landmark"> <div id="vector-toc-pinned-container" class="vector-pinned-container"> <div id="vector-toc" class="vector-toc vector-pinnable-element"> <div class="vector-pinnable-header vector-toc-pinnable-header vector-pinnable-header-pinned" data-feature-name="toc-pinned" data-pinnable-element-id="vector-toc" > <h2 class="vector-pinnable-header-label">Contents</h2> <button class="vector-pinnable-header-toggle-button vector-pinnable-header-pin-button" data-event-name="pinnable-header.vector-toc.pin">move to sidebar</button> <button class="vector-pinnable-header-toggle-button vector-pinnable-header-unpin-button" data-event-name="pinnable-header.vector-toc.unpin">hide</button> </div> <ul class="vector-toc-contents" id="mw-panel-toc-list"> <li id="toc-mw-content-text" class="vector-toc-list-item vector-toc-level-1"> <a href="#" class="vector-toc-link"> <div class="vector-toc-text">(Top)</div> </a> </li> <li id="toc-In_virtual_memory_management" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#In_virtual_memory_management"> <div class="vector-toc-text"> <span class="vector-toc-numb">1</span> <span>In virtual memory management</span> </div> </a> <ul id="toc-In_virtual_memory_management-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-In_software" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#In_software"> <div class="vector-toc-text"> <span class="vector-toc-numb">2</span> <span>In software</span> </div> </a> <button aria-controls="toc-In_software-sublist" class="cdx-button cdx-button--weight-quiet cdx-button--icon-only vector-toc-toggle"> <span class="vector-icon mw-ui-icon-wikimedia-expand"></span> <span>Toggle In software subsection</span> </button> <ul id="toc-In_software-sublist" class="vector-toc-list"> <li id="toc-Examples" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Examples"> <div class="vector-toc-text"> <span class="vector-toc-numb">2.1</span> <span>Examples</span> </div> </a> <ul id="toc-Examples-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-In_computer_storage" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#In_computer_storage"> <div class="vector-toc-text"> <span class="vector-toc-numb">3</span> <span>In computer storage</span> </div> </a> <ul id="toc-In_computer_storage-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-See_also" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#See_also"> <div class="vector-toc-text"> <span class="vector-toc-numb">4</span> <span>See also</span> </div> </a> <ul id="toc-See_also-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-References" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#References"> <div class="vector-toc-text"> <span class="vector-toc-numb">5</span> <span>References</span> </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 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#External_links"> <div class="vector-toc-text"> <span class="vector-toc-numb">6</span> <span>External links</span> </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" ><span class="vector-icon mw-ui-icon-listBullet mw-ui-icon-wikimedia-listBullet"></span> <span class="vector-dropdown-label-text">Toggle the table of contents</span> </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"><span class="mw-page-title-main">Copy-on-write</span></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 mw-interlanguage-selector" aria-label="Go to an article in another language. Available in 20 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-20" aria-hidden="true" ><span class="vector-icon mw-ui-icon-language-progressive mw-ui-icon-wikimedia-language-progressive"></span> <span class="vector-dropdown-label-text">20 languages</span> </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%A7%D9%84%D9%86%D8%B3%D8%AE_%D8%B9%D9%86%D8%AF_%D8%A7%D9%84%D9%83%D8%AA%D8%A7%D8%A8%D8%A9" title="النسخ عند الكتابة – Arabic" lang="ar" hreflang="ar" data-title="النسخ عند الكتابة" data-language-autonym="العربية" data-language-local-name="Arabic" class="interlanguage-link-target"><span>العربية</span></a></li><li class="interlanguage-link interwiki-cs mw-list-item"><a href="https://cs.wikipedia.org/wiki/Copy-on-write" title="Copy-on-write – Czech" lang="cs" hreflang="cs" data-title="Copy-on-write" data-language-autonym="Čeština" data-language-local-name="Czech" class="interlanguage-link-target"><span>Čeština</span></a></li><li class="interlanguage-link interwiki-de mw-list-item"><a href="https://de.wikipedia.org/wiki/Copy-On-Write" title="Copy-On-Write – German" lang="de" hreflang="de" data-title="Copy-On-Write" data-language-autonym="Deutsch" data-language-local-name="German" class="interlanguage-link-target"><span>Deutsch</span></a></li><li class="interlanguage-link interwiki-es mw-list-item"><a href="https://es.wikipedia.org/wiki/Copy-on-write" title="Copy-on-write – Spanish" lang="es" hreflang="es" data-title="Copy-on-write" data-language-autonym="Español" data-language-local-name="Spanish" class="interlanguage-link-target"><span>Español</span></a></li><li class="interlanguage-link interwiki-fa mw-list-item"><a href="https://fa.wikipedia.org/wiki/%DA%A9%D9%BE%DB%8C-%D8%AF%D8%B1-%D9%86%D9%88%D8%B4%D8%AA%D9%86" title="کپی-در-نوشتن – Persian" lang="fa" hreflang="fa" data-title="کپی-در-نوشتن" data-language-autonym="فارسی" data-language-local-name="Persian" class="interlanguage-link-target"><span>فارسی</span></a></li><li class="interlanguage-link interwiki-fr mw-list-item"><a href="https://fr.wikipedia.org/wiki/Copy-on-write" title="Copy-on-write – French" lang="fr" hreflang="fr" data-title="Copy-on-write" data-language-autonym="Français" data-language-local-name="French" class="interlanguage-link-target"><span>Français</span></a></li><li class="interlanguage-link interwiki-ko mw-list-item"><a href="https://ko.wikipedia.org/wiki/%EC%B9%B4%ED%94%BC_%EC%98%A8_%EB%9D%BC%EC%9D%B4%ED%8A%B8" title="카피 온 라이트 – Korean" lang="ko" hreflang="ko" data-title="카피 온 라이트" data-language-autonym="한국어" data-language-local-name="Korean" class="interlanguage-link-target"><span>한국어</span></a></li><li class="interlanguage-link interwiki-hr mw-list-item"><a href="https://hr.wikipedia.org/wiki/Copy-On-Write" title="Copy-On-Write – Croatian" lang="hr" hreflang="hr" data-title="Copy-On-Write" data-language-autonym="Hrvatski" data-language-local-name="Croatian" class="interlanguage-link-target"><span>Hrvatski</span></a></li><li class="interlanguage-link interwiki-it mw-list-item"><a href="https://it.wikipedia.org/wiki/Copy-on-write" title="Copy-on-write – Italian" lang="it" hreflang="it" data-title="Copy-on-write" data-language-autonym="Italiano" data-language-local-name="Italian" class="interlanguage-link-target"><span>Italiano</span></a></li><li class="interlanguage-link interwiki-he mw-list-item"><a href="https://he.wikipedia.org/wiki/%D7%94%D7%A2%D7%AA%D7%A7%D7%94_%D7%91%D7%96%D7%9E%D7%9F_%D7%9B%D7%AA%D7%99%D7%91%D7%94" title="העתקה בזמן כתיבה – Hebrew" lang="he" hreflang="he" data-title="העתקה בזמן כתיבה" data-language-autonym="עברית" data-language-local-name="Hebrew" class="interlanguage-link-target"><span>עברית</span></a></li><li class="interlanguage-link interwiki-ja mw-list-item"><a href="https://ja.wikipedia.org/wiki/%E3%82%B3%E3%83%94%E3%83%BC%E3%82%AA%E3%83%B3%E3%83%A9%E3%82%A4%E3%83%88" title="コピーオンライト – Japanese" lang="ja" hreflang="ja" data-title="コピーオンライト" data-language-autonym="日本語" data-language-local-name="Japanese" class="interlanguage-link-target"><span>日本語</span></a></li><li class="interlanguage-link interwiki-no mw-list-item"><a href="https://no.wikipedia.org/wiki/Copy-on-write" title="Copy-on-write – Norwegian Bokmål" lang="nb" hreflang="nb" data-title="Copy-on-write" data-language-autonym="Norsk bokmål" data-language-local-name="Norwegian Bokmål" class="interlanguage-link-target"><span>Norsk bokmål</span></a></li><li class="interlanguage-link interwiki-pl mw-list-item"><a href="https://pl.wikipedia.org/wiki/Kopiowanie_przy_zapisie" title="Kopiowanie przy zapisie – Polish" lang="pl" hreflang="pl" data-title="Kopiowanie przy zapisie" data-language-autonym="Polski" data-language-local-name="Polish" class="interlanguage-link-target"><span>Polski</span></a></li><li class="interlanguage-link interwiki-pt mw-list-item"><a href="https://pt.wikipedia.org/wiki/C%C3%B3pia_em_grava%C3%A7%C3%A3o" title="Cópia em gravação – Portuguese" lang="pt" hreflang="pt" data-title="Cópia em gravação" data-language-autonym="Português" data-language-local-name="Portuguese" class="interlanguage-link-target"><span>Português</span></a></li><li class="interlanguage-link interwiki-ru mw-list-item"><a href="https://ru.wikipedia.org/wiki/%D0%9A%D0%BE%D0%BF%D0%B8%D1%80%D0%BE%D0%B2%D0%B0%D0%BD%D0%B8%D0%B5_%D0%BF%D1%80%D0%B8_%D0%B7%D0%B0%D0%BF%D0%B8%D1%81%D0%B8" title="Копирование при записи – Russian" lang="ru" hreflang="ru" data-title="Копирование при записи" data-language-autonym="Русский" data-language-local-name="Russian" class="interlanguage-link-target"><span>Русский</span></a></li><li class="interlanguage-link interwiki-simple mw-list-item"><a href="https://simple.wikipedia.org/wiki/Copy-on-write" title="Copy-on-write – Simple English" lang="en-simple" hreflang="en-simple" data-title="Copy-on-write" data-language-autonym="Simple English" data-language-local-name="Simple English" class="interlanguage-link-target"><span>Simple English</span></a></li><li class="interlanguage-link interwiki-sv mw-list-item"><a href="https://sv.wikipedia.org/wiki/Copy-on-write" title="Copy-on-write – Swedish" lang="sv" hreflang="sv" data-title="Copy-on-write" data-language-autonym="Svenska" data-language-local-name="Swedish" class="interlanguage-link-target"><span>Svenska</span></a></li><li class="interlanguage-link interwiki-tr mw-list-item"><a href="https://tr.wikipedia.org/wiki/Copy-on-write" title="Copy-on-write – Turkish" lang="tr" hreflang="tr" data-title="Copy-on-write" data-language-autonym="Türkçe" data-language-local-name="Turkish" class="interlanguage-link-target"><span>Türkçe</span></a></li><li class="interlanguage-link interwiki-uk mw-list-item"><a href="https://uk.wikipedia.org/wiki/%D0%9A%D0%BE%D0%BF%D1%96%D1%8E%D0%B2%D0%B0%D0%BD%D0%BD%D1%8F_%D0%BF%D1%80%D0%B8_%D0%B7%D0%B0%D0%BF%D0%B8%D1%81%D1%83%D0%B2%D0%B0%D0%BD%D0%BD%D1%96" title="Копіювання при записуванні – Ukrainian" lang="uk" hreflang="uk" data-title="Копіювання при записуванні" data-language-autonym="Українська" data-language-local-name="Ukrainian" class="interlanguage-link-target"><span>Українська</span></a></li><li class="interlanguage-link interwiki-zh mw-list-item"><a href="https://zh.wikipedia.org/wiki/%E5%AF%AB%E5%85%A5%E6%99%82%E8%A4%87%E8%A3%BD" title="寫入時複製 – Chinese" lang="zh" hreflang="zh" data-title="寫入時複製" data-language-autonym="中文" data-language-local-name="Chinese" class="interlanguage-link-target"><span>中文</span></a></li> </ul> <div class="after-portlet after-portlet-lang"><span class="wb-langlinks-edit wb-langlinks-link"><a href="https://www.wikidata.org/wiki/Special:EntityPage/Q1131607#sitelinks-wikipedia" title="Edit interlanguage links" class="wbc-editpage">Edit links</a></span></div> </div> </div> </div> </header> <div class="vector-page-toolbar"> <div class="vector-page-toolbar-container"> <div id="left-navigation"> <nav aria-label="Namespaces"> <div id="p-associated-pages" class="vector-menu vector-menu-tabs mw-portlet mw-portlet-associated-pages" > <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li id="ca-nstab-main" class="selected vector-tab-noicon mw-list-item"><a href="/wiki/Copy-on-write" title="View the content page [c]" accesskey="c"><span>Article</span></a></li><li id="ca-talk" class="vector-tab-noicon mw-list-item"><a href="/wiki/Talk:Copy-on-write" rel="discussion" title="Discuss improvements to the content page [t]" accesskey="t"><span>Talk</span></a></li> </ul> </div> </div> <div id="vector-variants-dropdown" class="vector-dropdown emptyPortlet" > <input type="checkbox" id="vector-variants-dropdown-checkbox" role="button" aria-haspopup="true" data-event-name="ui.dropdown-vector-variants-dropdown" class="vector-dropdown-checkbox " aria-label="Change language variant" > <label id="vector-variants-dropdown-label" for="vector-variants-dropdown-checkbox" class="vector-dropdown-label cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet" aria-hidden="true" ><span class="vector-dropdown-label-text">English</span> </label> <div class="vector-dropdown-content"> <div id="p-variants" class="vector-menu mw-portlet mw-portlet-variants emptyPortlet" > <div class="vector-menu-content"> <ul class="vector-menu-content-list"> </ul> </div> </div> </div> </div> </nav> </div> <div id="right-navigation" class="vector-collapsible"> <nav aria-label="Views"> <div id="p-views" class="vector-menu vector-menu-tabs mw-portlet mw-portlet-views" > <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li id="ca-view" class="selected vector-tab-noicon mw-list-item"><a href="/wiki/Copy-on-write"><span>Read</span></a></li><li id="ca-edit" class="vector-tab-noicon mw-list-item"><a href="/w/index.php?title=Copy-on-write&action=edit" title="Edit this page [e]" accesskey="e"><span>Edit</span></a></li><li id="ca-history" class="vector-tab-noicon mw-list-item"><a href="/w/index.php?title=Copy-on-write&action=history" title="Past revisions of this page [h]" accesskey="h"><span>View history</span></a></li> </ul> </div> </div> </nav> <nav class="vector-page-tools-landmark" aria-label="Page tools"> <div id="vector-page-tools-dropdown" class="vector-dropdown vector-page-tools-dropdown" > <input type="checkbox" id="vector-page-tools-dropdown-checkbox" role="button" aria-haspopup="true" data-event-name="ui.dropdown-vector-page-tools-dropdown" class="vector-dropdown-checkbox " aria-label="Tools" > <label id="vector-page-tools-dropdown-label" for="vector-page-tools-dropdown-checkbox" class="vector-dropdown-label cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet" aria-hidden="true" ><span class="vector-dropdown-label-text">Tools</span> </label> <div class="vector-dropdown-content"> <div id="vector-page-tools-unpinned-container" class="vector-unpinned-container"> <div id="vector-page-tools" class="vector-page-tools vector-pinnable-element"> <div class="vector-pinnable-header vector-page-tools-pinnable-header vector-pinnable-header-unpinned" data-feature-name="page-tools-pinned" data-pinnable-element-id="vector-page-tools" data-pinned-container-id="vector-page-tools-pinned-container" data-unpinned-container-id="vector-page-tools-unpinned-container" > <div class="vector-pinnable-header-label">Tools</div> <button class="vector-pinnable-header-toggle-button vector-pinnable-header-pin-button" data-event-name="pinnable-header.vector-page-tools.pin">move to sidebar</button> <button class="vector-pinnable-header-toggle-button vector-pinnable-header-unpin-button" data-event-name="pinnable-header.vector-page-tools.unpin">hide</button> </div> <div id="p-cactions" class="vector-menu mw-portlet mw-portlet-cactions emptyPortlet vector-has-collapsible-items" title="More options" > <div class="vector-menu-heading"> Actions </div> <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li id="ca-more-view" class="selected vector-more-collapsible-item mw-list-item"><a href="/wiki/Copy-on-write"><span>Read</span></a></li><li id="ca-more-edit" class="vector-more-collapsible-item mw-list-item"><a href="/w/index.php?title=Copy-on-write&action=edit" title="Edit this page [e]" accesskey="e"><span>Edit</span></a></li><li id="ca-more-history" class="vector-more-collapsible-item mw-list-item"><a href="/w/index.php?title=Copy-on-write&action=history"><span>View history</span></a></li> </ul> </div> </div> <div id="p-tb" class="vector-menu mw-portlet mw-portlet-tb" > <div class="vector-menu-heading"> General </div> <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li id="t-whatlinkshere" class="mw-list-item"><a href="/wiki/Special:WhatLinksHere/Copy-on-write" title="List of all English Wikipedia pages containing links to this page [j]" accesskey="j"><span>What links here</span></a></li><li id="t-recentchangeslinked" class="mw-list-item"><a href="/wiki/Special:RecentChangesLinked/Copy-on-write" rel="nofollow" title="Recent changes in pages linked from this page [k]" accesskey="k"><span>Related changes</span></a></li><li id="t-upload" class="mw-list-item"><a href="/wiki/Wikipedia:File_Upload_Wizard" title="Upload files [u]" accesskey="u"><span>Upload file</span></a></li><li id="t-specialpages" class="mw-list-item"><a href="/wiki/Special:SpecialPages" title="A list of all special pages [q]" accesskey="q"><span>Special pages</span></a></li><li id="t-permalink" class="mw-list-item"><a href="/w/index.php?title=Copy-on-write&oldid=1258225312" title="Permanent link to this revision of this page"><span>Permanent link</span></a></li><li id="t-info" class="mw-list-item"><a href="/w/index.php?title=Copy-on-write&action=info" title="More information about this page"><span>Page information</span></a></li><li id="t-cite" class="mw-list-item"><a href="/w/index.php?title=Special:CiteThisPage&page=Copy-on-write&id=1258225312&wpFormIdentifier=titleform" title="Information on how to cite this page"><span>Cite this page</span></a></li><li id="t-urlshortener" class="mw-list-item"><a href="/w/index.php?title=Special:UrlShortener&url=https%3A%2F%2Fen.wikipedia.org%2Fwiki%2FCopy-on-write"><span>Get shortened URL</span></a></li><li id="t-urlshortener-qrcode" class="mw-list-item"><a href="/w/index.php?title=Special:QrCode&url=https%3A%2F%2Fen.wikipedia.org%2Fwiki%2FCopy-on-write"><span>Download QR code</span></a></li> </ul> </div> </div> <div id="p-coll-print_export" class="vector-menu mw-portlet mw-portlet-coll-print_export" > <div class="vector-menu-heading"> Print/export </div> <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li id="coll-download-as-rl" class="mw-list-item"><a href="/w/index.php?title=Special:DownloadAsPdf&page=Copy-on-write&action=show-download-screen" title="Download this page as a PDF file"><span>Download as PDF</span></a></li><li id="t-print" class="mw-list-item"><a href="/w/index.php?title=Copy-on-write&printable=yes" title="Printable version of this page [p]" accesskey="p"><span>Printable version</span></a></li> </ul> </div> </div> <div id="p-wikibase-otherprojects" class="vector-menu mw-portlet mw-portlet-wikibase-otherprojects" > <div class="vector-menu-heading"> In other projects </div> <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li class="wb-otherproject-link wb-otherproject-commons mw-list-item"><a href="https://commons.wikimedia.org/wiki/Category:Copy-on-write" hreflang="en"><span>Wikimedia Commons</span></a></li><li id="t-wikibase" class="wb-otherproject-link wb-otherproject-wikibase-dataitem mw-list-item"><a href="https://www.wikidata.org/wiki/Special:EntityPage/Q1131607" title="Structured data on this page hosted by Wikidata [g]" accesskey="g"><span>Wikidata item</span></a></li> </ul> </div> </div> </div> </div> </div> </div> </nav> </div> </div> </div> <div class="vector-column-end"> <div class="vector-sticky-pinned-container"> <nav class="vector-page-tools-landmark" aria-label="Page tools"> <div id="vector-page-tools-pinned-container" class="vector-pinned-container"> </div> </nav> <nav class="vector-appearance-landmark" aria-label="Appearance"> <div id="vector-appearance-pinned-container" class="vector-pinned-container"> <div id="vector-appearance" class="vector-appearance vector-pinnable-element"> <div class="vector-pinnable-header vector-appearance-pinnable-header vector-pinnable-header-pinned" data-feature-name="appearance-pinned" data-pinnable-element-id="vector-appearance" data-pinned-container-id="vector-appearance-pinned-container" data-unpinned-container-id="vector-appearance-unpinned-container" > <div class="vector-pinnable-header-label">Appearance</div> <button class="vector-pinnable-header-toggle-button vector-pinnable-header-pin-button" data-event-name="pinnable-header.vector-appearance.pin">move to sidebar</button> <button class="vector-pinnable-header-toggle-button vector-pinnable-header-unpin-button" data-event-name="pinnable-header.vector-appearance.unpin">hide</button> </div> </div> </div> </nav> </div> </div> <div id="bodyContent" class="vector-body" aria-labelledby="firstHeading" 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"></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">Programming technique for efficiently duplicating data</div> <p class="mw-empty-elt"> </p><p><b>Copy-on-write</b> (<b>COW</b>), also called <b>implicit sharing</b><sup id="cite_ref-1" class="reference"><a href="#cite_note-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup> or <b>shadowing</b>,<sup id="cite_ref-2" class="reference"><a href="#cite_note-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup> is a <a href="/wiki/Resource_management_(computing)" title="Resource management (computing)">resource-management</a> technique<sup id="cite_ref-Linux_3-0" class="reference"><a href="#cite_note-Linux-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup> used in <a href="/wiki/Computer_programming" title="Computer programming">programming</a> to manage shared data efficiently. Instead of copying data right away when multiple programs use it, the same data is shared between programs until one tries to modify it. If no changes are made, no private copy is created, saving <a href="/wiki/System_resource#General_resources" title="System resource">resources</a>.<sup id="cite_ref-Linux_3-1" class="reference"><a href="#cite_note-Linux-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup> A copy is only made when needed, ensuring each program has its own version when modifications occur. This technique is commonly applied to memory, files, and data structures. </p> <meta property="mw:PageProp/toc" /> <div class="mw-heading mw-heading2"><h2 id="In_virtual_memory_management">In virtual memory management</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Copy-on-write&action=edit&section=1" title="Edit section: In virtual memory management"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Copy-on-write finds its main use in <a href="/wiki/Operating_system" title="Operating system">operating systems</a>, sharing the <a href="/wiki/Physical_memory" class="mw-redirect" title="Physical memory">physical memory</a> of computers running multiple <a href="/wiki/Process_(computing)" title="Process (computing)">processes</a>, in the implementation of the <a href="/wiki/Fork_(system_call)" title="Fork (system call)">fork() system call</a>. Typically, the new process does not modify any memory and immediately executes a new process, replacing the address space entirely. It would waste processor time and memory to copy all of the old process's memory during the fork only to immediately discard the copy.<sup id="cite_ref-4" class="reference"><a href="#cite_note-4"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup> </p><p>Copy-on-write can be implemented efficiently using the <a href="/wiki/Page_table" title="Page table">page table</a> by marking certain pages of <a href="/wiki/Computer_storage" class="mw-redirect" title="Computer storage">memory</a> as read-only and keeping a count of the number of references to the page. When data is written to these pages, the operating-system <a href="/wiki/Kernel_(operating_system)" title="Kernel (operating system)">kernel</a> intercepts the write attempt and allocates a new physical page, initialized with the copy-on-write data, although the allocation can be skipped if there is only one reference. The kernel then updates the page table with the new (writable) page, decrements the number of references, and performs the write. The new allocation ensures that a change in the memory of one process is not visible in another's.<sup class="noprint Inline-Template Template-Fact" style="white-space:nowrap;">[<i><a href="/wiki/Wikipedia:Citation_needed" title="Wikipedia:Citation needed"><span title="This claim needs references to reliable sources. (November 2023)">citation needed</span></a></i>]</sup> </p><p>The copy-on-write technique can be extended to support efficient <a href="/wiki/Memory_allocation" class="mw-redirect" title="Memory allocation">memory allocation</a> by keeping one page of <a href="/wiki/Physical_memory" class="mw-redirect" title="Physical memory">physical memory</a> filled with zeros. When the memory is allocated, all the pages returned refer to the page of zeros and are all marked copy-on-write. This way, physical memory is not allocated for the process until data is written, allowing processes to reserve more virtual memory than physical memory and use memory sparsely, at the risk of running out of virtual address space. The combined algorithm is similar to <a href="/wiki/Demand_paging" title="Demand paging">demand paging</a>.<sup id="cite_ref-Linux_3-2" class="reference"><a href="#cite_note-Linux-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup> </p><p>Copy-on-write pages are also used in the <a href="/wiki/Linux_kernel" title="Linux kernel">Linux kernel</a>'s <a href="/wiki/Kernel_same-page_merging" title="Kernel same-page merging">same-page merging</a> feature.<sup id="cite_ref-5" class="reference"><a href="#cite_note-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading2"><h2 id="In_software">In software</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Copy-on-write&action=edit&section=2" title="Edit section: In software"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></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-Expand_section plainlinks metadata ambox mbox-small-left ambox-content" role="presentation"><tbody><tr><td class="mbox-image"><span typeof="mw:File"><a href="/wiki/File:Wiki_letter_w_cropped.svg" class="mw-file-description"><img alt="[icon]" src="//upload.wikimedia.org/wikipedia/commons/thumb/1/1c/Wiki_letter_w_cropped.svg/20px-Wiki_letter_w_cropped.svg.png" decoding="async" width="20" height="14" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/1/1c/Wiki_letter_w_cropped.svg/30px-Wiki_letter_w_cropped.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/1/1c/Wiki_letter_w_cropped.svg/40px-Wiki_letter_w_cropped.svg.png 2x" data-file-width="44" data-file-height="31" /></a></span></td><td class="mbox-text"><div class="mbox-text-span">This section <b>needs expansion</b>. You can help by <a class="external text" href="https://en.wikipedia.org/w/index.php?title=Copy-on-write&action=edit&section=">adding to it</a>. <span class="date-container"><i>(<span class="date">October 2017</span>)</i></span></div></td></tr></tbody></table> <p>COW is also used in <a href="/wiki/Library_(computer_science)" class="mw-redirect" title="Library (computer science)">library</a>, <a href="/wiki/Application_software" title="Application software">application</a>, and <a href="/wiki/System_software" title="System software">system</a> code. </p> <div class="mw-heading mw-heading3"><h3 id="Examples">Examples</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Copy-on-write&action=edit&section=3" title="Edit section: Examples"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The <a href="/wiki/String_(C%2B%2B)" class="mw-redirect" title="String (C++)">string</a> class provided by the <a href="/wiki/C%2B%2B_standard_library" class="mw-redirect" title="C++ standard library">C++ standard library</a> was specifically designed to allow copy-on-write implementations in the initial C++98 standard,<sup id="cite_ref-meyers_6-0" class="reference"><a href="#cite_note-meyers-6"><span class="cite-bracket">[</span>6<span class="cite-bracket">]</span></a></sup> but not in the newer C++11 standard:<sup id="cite_ref-7" class="reference"><a href="#cite_note-7"><span class="cite-bracket">[</span>7<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-highlight mw-highlight-lang-cpp mw-content-ltr" dir="ltr"><pre><span></span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="w"> </span><span class="n">x</span><span class="p">(</span><span class="s">"Hello"</span><span class="p">);</span> <span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">x</span><span class="p">;</span><span class="w"> </span><span class="c1">// x and y use the same buffer.</span> <span class="n">y</span><span class="w"> </span><span class="o">+=</span><span class="w"> </span><span class="s">", World!"</span><span class="p">;</span><span class="w"> </span><span class="c1">// Now y uses a different buffer; x still uses the same old buffer.</span> </pre></div> <p>In the <a href="/wiki/PHP" title="PHP">PHP</a> programming language, all types except references are implemented as copy-on-write. For example, strings and arrays are passed by reference, but when modified, they are duplicated if they have non-zero reference counts. This allows them to act as value types without the performance problems of copying on assignment or making them immutable.<sup id="cite_ref-8" class="reference"><a href="#cite_note-8"><span class="cite-bracket">[</span>8<span class="cite-bracket">]</span></a></sup> </p><p>In the <a href="/wiki/Qt_(software)" title="Qt (software)">Qt</a> framework, many types are copy-on-write ("implicitly shared" in Qt's terms). Qt uses atomic <a href="/wiki/Compare-and-swap" title="Compare-and-swap">compare-and-swap</a> operations to increment or decrement the internal reference counter. Since the copies are cheap, Qt types can often be safely used by <a href="/wiki/Multithreading_(computer_architecture)" title="Multithreading (computer architecture)">multiple threads</a> without the need of <a href="/wiki/Lock_(computer_science)" title="Lock (computer science)">locking mechanisms</a> such as <a href="/wiki/Mutual_exclusion" title="Mutual exclusion">mutexes</a>. The benefits of COW are thus valid in both single- and multithreaded systems.<sup id="cite_ref-9" class="reference"><a href="#cite_note-9"><span class="cite-bracket">[</span>9<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading2"><h2 id="In_computer_storage">In computer storage</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Copy-on-write&action=edit&section=4" title="Edit section: In computer storage"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>COW is used as the underlying mechanism in file systems like <a href="/wiki/ZFS" title="ZFS">ZFS</a>, <a href="/wiki/Btrfs" title="Btrfs">Btrfs</a>, <a href="/wiki/ReFS" title="ReFS">ReFS</a>, and <a href="/wiki/Bcachefs" title="Bcachefs">Bcachefs</a>,<sup id="cite_ref-10" class="reference"><a href="#cite_note-10"><span class="cite-bracket">[</span>10<span class="cite-bracket">]</span></a></sup> as well as in <a href="/wiki/Logical_volume_management" title="Logical volume management">logical volume management</a> and database servers such as <a href="/wiki/Microsoft_SQL_Server#Replication_Services" title="Microsoft SQL Server">Microsoft SQL Server</a>. </p><p>In traditional file systems, file changes overwrite the original data. With COW, when changes are made, a new version of the file is created while keeping the original intact. This approach enables features like <a href="/wiki/Snapshot_(computer_storage)" title="Snapshot (computer storage)">snapshots</a>, which capture the state of a file at a specific time without consuming much additional space. Snapshots typically store only the modified data and are kept close to the original. However, they are considered a weak form of <a href="/wiki/Incremental_backup" title="Incremental backup">incremental backup</a> and cannot replace a full backup.<sup id="cite_ref-11" class="reference"><a href="#cite_note-11"><span class="cite-bracket">[</span>11<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading2"><h2 id="See_also">See also</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Copy-on-write&action=edit&section=5" title="Edit section: See also"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <ul><li><a href="/wiki/Allocate-on-flush" title="Allocate-on-flush">Allocate-on-flush</a></li> <li><a href="/wiki/Dirty_COW" title="Dirty COW">Dirty COW</a> – a computer security vulnerability for the Linux kernel</li> <li><a href="/wiki/Flyweight_pattern" title="Flyweight pattern">Flyweight pattern</a></li> <li><a href="/wiki/Memory_management" title="Memory management">Memory management</a></li> <li><a href="/wiki/Persistent_data_structure" title="Persistent data structure">Persistent data structure</a></li> <li><a href="/wiki/Wear_leveling" title="Wear leveling">Wear leveling</a></li></ul> <div class="mw-heading mw-heading2"><h2 id="References">References</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Copy-on-write&action=edit&section=6" title="Edit section: References"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <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 mw-references-columns"><ol class="references"> <li id="cite_note-1"><span class="mw-cite-backlink"><b><a href="#cite_ref-1">^</a></b></span> <span class="reference-text"><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="https://doc.qt.io/qt-5/implicit-sharing.html">"Implicit Sharing"</a>. <i>Qt Project</i>. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20240208175543/https://doc.qt.io/qt-5/implicit-sharing.html">Archived</a> from the original on 8 February 2024<span class="reference-accessdate">. Retrieved <span class="nowrap">10 November</span> 2023</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=Qt+Project&rft.atitle=Implicit+Sharing&rft_id=https%3A%2F%2Fdoc.qt.io%2Fqt-5%2Fimplicit-sharing.html&rfr_id=info%3Asid%2Fen.wikipedia.org%3ACopy-on-write" class="Z3988"></span></span> </li> <li id="cite_note-2"><span class="mw-cite-backlink"><b><a href="#cite_ref-2">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFRodeh2008" class="citation journal cs1">Rodeh, Ohad (1 February 2008). <a rel="nofollow" class="external text" href="https://web.archive.org/web/20170102212904/http://liw.fi/larch/ohad-btrees-shadowing-clones.pdf">"B-Trees, Shadowing, and Clones"</a> <span class="cs1-format">(PDF)</span>. <i>ACM Transactions on Storage</i>. <b>3</b> (4): 1. <a href="/wiki/CiteSeerX_(identifier)" class="mw-redirect" title="CiteSeerX (identifier)">CiteSeerX</a> <span class="id-lock-free" title="Freely accessible"><a rel="nofollow" class="external text" href="https://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.161.6863">10.1.1.161.6863</a></span>. <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1145%2F1326542.1326544">10.1145/1326542.1326544</a>. <a href="/wiki/S2CID_(identifier)" class="mw-redirect" title="S2CID (identifier)">S2CID</a> <a rel="nofollow" class="external text" href="https://api.semanticscholar.org/CorpusID:207166167">207166167</a>. Archived from <a rel="nofollow" class="external text" href="http://liw.fi/larch/ohad-btrees-shadowing-clones.pdf">the original</a> <span class="cs1-format">(PDF)</span> on 2 January 2017<span class="reference-accessdate">. Retrieved <span class="nowrap">10 November</span> 2023</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=ACM+Transactions+on+Storage&rft.atitle=B-Trees%2C+Shadowing%2C+and+Clones&rft.volume=3&rft.issue=4&rft.pages=1&rft.date=2008-02-01&rft_id=https%3A%2F%2Fciteseerx.ist.psu.edu%2Fviewdoc%2Fsummary%3Fdoi%3D10.1.1.161.6863%23id-name%3DCiteSeerX&rft_id=https%3A%2F%2Fapi.semanticscholar.org%2FCorpusID%3A207166167%23id-name%3DS2CID&rft_id=info%3Adoi%2F10.1145%2F1326542.1326544&rft.aulast=Rodeh&rft.aufirst=Ohad&rft_id=http%3A%2F%2Fliw.fi%2Flarch%2Fohad-btrees-shadowing-clones.pdf&rfr_id=info%3Asid%2Fen.wikipedia.org%3ACopy-on-write" class="Z3988"></span></span> </li> <li id="cite_note-Linux-3"><span class="mw-cite-backlink">^ <a href="#cite_ref-Linux_3-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-Linux_3-1"><sup><i><b>b</b></i></sup></a> <a href="#cite_ref-Linux_3-2"><sup><i><b>c</b></i></sup></a></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFBovetCesati2002" class="citation book cs1">Bovet, Daniel Pierre; Cesati, Marco (1 January 2002). <a rel="nofollow" class="external text" href="https://books.google.com/books?id=9yIEji1UheIC&q=%22copy%20on%20write%22&pg=PA295"><i>Understanding the Linux Kernel</i></a>. O'Reilly Media. p. 295. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/9780596002138" title="Special:BookSources/9780596002138"><bdi>9780596002138</bdi></a>. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20240915132745/https://books.google.com/books?id=9yIEji1UheIC&q=%22copy%20on%20write%22&pg=PA295#v=snippet&q=%22copy%20on%20write%22&f=false">Archived</a> from the original on 15 September 2024<span class="reference-accessdate">. Retrieved <span class="nowrap">10 November</span> 2023</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Understanding+the+Linux+Kernel&rft.pages=295&rft.pub=O%27Reilly+Media&rft.date=2002-01-01&rft.isbn=9780596002138&rft.aulast=Bovet&rft.aufirst=Daniel+Pierre&rft.au=Cesati%2C+Marco&rft_id=https%3A%2F%2Fbooks.google.com%2Fbooks%3Fid%3D9yIEji1UheIC%26q%3D%2522copy%2520on%2520write%2522%26pg%3DPA295&rfr_id=info%3Asid%2Fen.wikipedia.org%3ACopy-on-write" class="Z3988"></span></span> </li> <li id="cite_note-4"><span class="mw-cite-backlink"><b><a href="#cite_ref-4">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFSilberschatzGalvin,_Peter_B.Gagne2018" class="citation book cs1">Silberschatz, Abraham; Galvin, Peter B.; Gagne, Greg (2018). <i>Operating System Concepts</i> (10th ed.). Wiley. pp. 120–123. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/978-1119456339" title="Special:BookSources/978-1119456339"><bdi>978-1119456339</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Operating+System+Concepts&rft.pages=120-123&rft.edition=10th&rft.pub=Wiley&rft.date=2018&rft.isbn=978-1119456339&rft.aulast=Silberschatz&rft.aufirst=Abraham&rft.au=Galvin%2C+Peter+B.&rft.au=Gagne%2C+Greg&rfr_id=info%3Asid%2Fen.wikipedia.org%3ACopy-on-write" class="Z3988"></span></span> </li> <li id="cite_note-5"><span class="mw-cite-backlink"><b><a href="#cite_ref-5">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFAbbas" class="citation web cs1">Abbas, Ali. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20160808174912/http://alouche.net/blog/2011/07/18/the-kernel-samepage-merging-process/">"The Kernel Samepage Merging Process"</a>. <i>alouche.net</i>. Archived from the original on 8 August 2016<span class="reference-accessdate">. Retrieved <span class="nowrap">10 November</span> 2023</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=alouche.net&rft.atitle=The+Kernel+Samepage+Merging+Process&rft.aulast=Abbas&rft.aufirst=Ali&rft_id=http%3A%2F%2Falouche.net%2Fblog%2F2011%2F07%2F18%2Fthe-kernel-samepage-merging-process%2F&rfr_id=info%3Asid%2Fen.wikipedia.org%3ACopy-on-write" class="Z3988"></span><span class="cs1-maint citation-comment"><code class="cs1-code">{{<a href="/wiki/Template:Cite_web" title="Template:Cite web">cite web</a>}}</code>: CS1 maint: unfit URL (<a href="/wiki/Category:CS1_maint:_unfit_URL" title="Category:CS1 maint: unfit URL">link</a>)</span></span> </li> <li id="cite_note-meyers-6"><span class="mw-cite-backlink"><b><a href="#cite_ref-meyers_6-0">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFMeyers2012" class="citation book cs1"><a href="/wiki/Scott_Meyers" title="Scott Meyers">Meyers, Scott</a> (2012). <i>Effective STL</i>. Addison-Wesley. pp. 64–65. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/9780132979184" title="Special:BookSources/9780132979184"><bdi>9780132979184</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Effective+STL&rft.pages=64-65&rft.pub=Addison-Wesley&rft.date=2012&rft.isbn=9780132979184&rft.aulast=Meyers&rft.aufirst=Scott&rfr_id=info%3Asid%2Fen.wikipedia.org%3ACopy-on-write" class="Z3988"></span></span> </li> <li id="cite_note-7"><span class="mw-cite-backlink"><b><a href="#cite_ref-7">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2534.html">"Concurrency Modifications to Basic String"</a>. <i>Open Standards</i>. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20231110024434/https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2534.html">Archived</a> from the original on 10 November 2023<span class="reference-accessdate">. Retrieved <span class="nowrap">10 November</span> 2023</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=Open+Standards&rft.atitle=Concurrency+Modifications+to+Basic+String&rft_id=https%3A%2F%2Fwww.open-std.org%2Fjtc1%2Fsc22%2Fwg21%2Fdocs%2Fpapers%2F2008%2Fn2534.html&rfr_id=info%3Asid%2Fen.wikipedia.org%3ACopy-on-write" class="Z3988"></span></span> </li> <li id="cite_note-8"><span class="mw-cite-backlink"><b><a href="#cite_ref-8">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFPauliFerraraPopov2013" class="citation web cs1">Pauli, Julien; Ferrara, Anthony; Popov, Nikita (2013). <a rel="nofollow" class="external text" href="https://www.phpinternalsbook.com/php5/zvals/memory_management.html#reference-counting-and-copy-on-write">"Memory management"</a>. <i>PhpInternalsBook.com</i>. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20231110024435/https://www.phpinternalsbook.com/php5/zvals/memory_management.html#reference-counting-and-copy-on-write">Archived</a> from the original on 10 November 2023<span class="reference-accessdate">. Retrieved <span class="nowrap">10 November</span> 2023</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=PhpInternalsBook.com&rft.atitle=Memory+management&rft.date=2013&rft.aulast=Pauli&rft.aufirst=Julien&rft.au=Ferrara%2C+Anthony&rft.au=Popov%2C+Nikita&rft_id=https%3A%2F%2Fwww.phpinternalsbook.com%2Fphp5%2Fzvals%2Fmemory_management.html%23reference-counting-and-copy-on-write&rfr_id=info%3Asid%2Fen.wikipedia.org%3ACopy-on-write" class="Z3988"></span></span> </li> <li id="cite_note-9"><span class="mw-cite-backlink"><b><a href="#cite_ref-9">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://doc.qt.io/qt-5/threads-modules.html#threads-and-implicitly-shared-classes">"Threads and Implicitly Shared Classes"</a>. <i>Qt Project</i>. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20231203002914/https://doc.qt.io/QT-5/threads-modules.html#threads-and-implicitly-shared-classes">Archived</a> from the original on 3 December 2023<span class="reference-accessdate">. Retrieved <span class="nowrap">10 November</span> 2023</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=Qt+Project&rft.atitle=Threads+and+Implicitly+Shared+Classes&rft_id=https%3A%2F%2Fdoc.qt.io%2Fqt-5%2Fthreads-modules.html%23threads-and-implicitly-shared-classes&rfr_id=info%3Asid%2Fen.wikipedia.org%3ACopy-on-write" class="Z3988"></span></span> </li> <li id="cite_note-10"><span class="mw-cite-backlink"><b><a href="#cite_ref-10">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFKasampalis2010" class="citation web cs1">Kasampalis, Sakis (2010). <a rel="nofollow" class="external text" href="https://sakisk.me/files/copy-on-write-based-file-systems.pdf">"Copy-on-Write Based File Systems Performance Analysis and Implementation"</a> <span class="cs1-format">(PDF)</span>. p. 19. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20240505220510/https://sakisk.me/files/copy-on-write-based-file-systems.pdf">Archived</a> <span class="cs1-format">(PDF)</span> from the original on 5 May 2024<span class="reference-accessdate">. Retrieved <span class="nowrap">10 November</span> 2023</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=Copy-on-Write+Based+File+Systems+Performance+Analysis+and+Implementation&rft.pages=19&rft.date=2010&rft.aulast=Kasampalis&rft.aufirst=Sakis&rft_id=https%3A%2F%2Fsakisk.me%2Ffiles%2Fcopy-on-write-based-file-systems.pdf&rfr_id=info%3Asid%2Fen.wikipedia.org%3ACopy-on-write" class="Z3988"></span></span> </li> <li id="cite_note-11"><span class="mw-cite-backlink"><b><a href="#cite_ref-11">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFChien" class="citation web cs1">Chien, Tim. <a rel="nofollow" class="external text" href="https://www.oracle.com/database/technologies/rman-fra-snapshot.html">"Snapshots Are NOT Backups"</a>. <i>Oracle.com</i>. Oracle. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20231110024434/https://www.oracle.com/database/technologies/rman-fra-snapshot.html">Archived</a> from the original on 10 November 2023<span class="reference-accessdate">. Retrieved <span class="nowrap">10 November</span> 2023</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=Oracle.com&rft.atitle=Snapshots+Are+NOT+Backups&rft.aulast=Chien&rft.aufirst=Tim&rft_id=https%3A%2F%2Fwww.oracle.com%2Fdatabase%2Ftechnologies%2Frman-fra-snapshot.html&rfr_id=info%3Asid%2Fen.wikipedia.org%3ACopy-on-write" class="Z3988"></span></span> </li> </ol></div></div> <div class="mw-heading mw-heading2"><h2 id="External_links">External links</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Copy-on-write&action=edit&section=7" title="Edit section: External links"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <ul><li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://obvious.services.net/2011/01/history-of-copy-on-write-memory.html">"A history of copy-on-write memory management"</a>. <i>A keen grasp of the obvious</i>. 21 January 2011<span class="reference-accessdate">. Retrieved <span class="nowrap">18 November</span> 2024</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=A+keen+grasp+of+the+obvious&rft.atitle=A+history+of+copy-on-write+memory+management&rft.date=2011-01-21&rft_id=https%3A%2F%2Fobvious.services.net%2F2011%2F01%2Fhistory-of-copy-on-write-memory.html&rfr_id=info%3Asid%2Fen.wikipedia.org%3ACopy-on-write" class="Z3988"></span></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 .hlist li::after{content:" · ";font-weight:bold}.mw-parser-output .hlist dd:last-child::after,.mw-parser-output .hlist dt:last-child::after,.mw-parser-output .hlist li:last-child::after{content:none}.mw-parser-output .hlist dd dd:first-child::before,.mw-parser-output .hlist dd dt:first-child::before,.mw-parser-output .hlist dd li:first-child::before,.mw-parser-output .hlist dt dd:first-child::before,.mw-parser-output .hlist dt dt:first-child::before,.mw-parser-output .hlist dt li:first-child::before,.mw-parser-output .hlist li dd:first-child::before,.mw-parser-output .hlist li dt:first-child::before,.mw-parser-output .hlist li li:first-child::before{content:" (";font-weight:normal}.mw-parser-output .hlist dd dd:last-child::after,.mw-parser-output .hlist dd dt:last-child::after,.mw-parser-output .hlist dd li:last-child::after,.mw-parser-output .hlist dt dd:last-child::after,.mw-parser-output .hlist dt dt:last-child::after,.mw-parser-output .hlist dt li:last-child::after,.mw-parser-output .hlist li dd:last-child::after,.mw-parser-output .hlist li dt:last-child::after,.mw-parser-output .hlist li li:last-child::after{content:")";font-weight:normal}.mw-parser-output .hlist ol{counter-reset:listitem}.mw-parser-output .hlist ol>li{counter-increment:listitem}.mw-parser-output .hlist ol>li::before{content:" "counter(listitem)"\a0 "}.mw-parser-output .hlist dd ol>li:first-child::before,.mw-parser-output .hlist dt ol>li:first-child::before,.mw-parser-output .hlist li ol>li:first-child::before{content:" ("counter(listitem)"\a0 "}</style><style data-mw-deduplicate="TemplateStyles:r1236075235">.mw-parser-output .navbox{box-sizing:border-box;border:1px solid #a2a9b1;width:100%;clear:both;font-size:88%;text-align:center;padding:1px;margin:1em auto 0}.mw-parser-output .navbox .navbox{margin-top:0}.mw-parser-output .navbox+.navbox,.mw-parser-output .navbox+.navbox-styles+.navbox{margin-top:-1px}.mw-parser-output .navbox-inner,.mw-parser-output .navbox-subgroup{width:100%}.mw-parser-output .navbox-group,.mw-parser-output .navbox-title,.mw-parser-output .navbox-abovebelow{padding:0.25em 1em;line-height:1.5em;text-align:center}.mw-parser-output .navbox-group{white-space:nowrap;text-align:right}.mw-parser-output .navbox,.mw-parser-output .navbox-subgroup{background-color:#fdfdfd}.mw-parser-output .navbox-list{line-height:1.5em;border-color:#fdfdfd}.mw-parser-output .navbox-list-with-group{text-align:left;border-left-width:2px;border-left-style:solid}.mw-parser-output tr+tr>.navbox-abovebelow,.mw-parser-output tr+tr>.navbox-group,.mw-parser-output tr+tr>.navbox-image,.mw-parser-output tr+tr>.navbox-list{border-top:2px solid #fdfdfd}.mw-parser-output .navbox-title{background-color:#ccf}.mw-parser-output .navbox-abovebelow,.mw-parser-output .navbox-group,.mw-parser-output .navbox-subgroup .navbox-title{background-color:#ddf}.mw-parser-output .navbox-subgroup .navbox-group,.mw-parser-output .navbox-subgroup .navbox-abovebelow{background-color:#e6e6ff}.mw-parser-output .navbox-even{background-color:#f7f7f7}.mw-parser-output .navbox-odd{background-color:transparent}.mw-parser-output .navbox .hlist td dl,.mw-parser-output .navbox .hlist td ol,.mw-parser-output .navbox .hlist td ul,.mw-parser-output .navbox td.hlist dl,.mw-parser-output .navbox td.hlist ol,.mw-parser-output .navbox td.hlist ul{padding:0.125em 0}.mw-parser-output .navbox .navbar{display:block;font-size:100%}.mw-parser-output .navbox-title .navbar{float:left;text-align:left;margin-right:0.5em}body.skin--responsive .mw-parser-output .navbox-image img{max-width:none!important}@media print{body.ns-0 .mw-parser-output .navbox{display:none!important}}</style></div><div role="navigation" class="navbox" aria-labelledby="File_systems" style="padding:3px"><table class="nowraplinks hlist mw-collapsible autocollapse navbox-inner" style="border-spacing:0;background:transparent;color:inherit"><tbody><tr><th scope="col" class="navbox-title" colspan="2"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1129693374"><style data-mw-deduplicate="TemplateStyles:r1239400231">.mw-parser-output .navbar{display:inline;font-size:88%;font-weight:normal}.mw-parser-output .navbar-collapse{float:left;text-align:left}.mw-parser-output .navbar-boxtext{word-spacing:0}.mw-parser-output .navbar ul{display:inline-block;white-space:nowrap;line-height:inherit}.mw-parser-output .navbar-brackets::before{margin-right:-0.125em;content:"[ "}.mw-parser-output .navbar-brackets::after{margin-left:-0.125em;content:" ]"}.mw-parser-output .navbar li{word-spacing:-0.125em}.mw-parser-output .navbar a>span,.mw-parser-output .navbar a>abbr{text-decoration:inherit}.mw-parser-output .navbar-mini abbr{font-variant:small-caps;border-bottom:none;text-decoration:none;cursor:inherit}.mw-parser-output .navbar-ct-full{font-size:114%;margin:0 7em}.mw-parser-output .navbar-ct-mini{font-size:114%;margin:0 4em}html.skin-theme-clientpref-night .mw-parser-output .navbar li a abbr{color:var(--color-base)!important}@media(prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .navbar li a abbr{color:var(--color-base)!important}}@media print{.mw-parser-output .navbar{display:none!important}}</style><div class="navbar plainlinks hlist navbar-mini"><ul><li class="nv-view"><a href="/wiki/Template:File_systems" title="Template:File systems"><abbr title="View this template">v</abbr></a></li><li class="nv-talk"><a href="/wiki/Template_talk:File_systems" title="Template talk:File systems"><abbr title="Discuss this template">t</abbr></a></li><li class="nv-edit"><a href="/wiki/Special:EditPage/Template:File_systems" title="Special:EditPage/Template:File systems"><abbr title="Edit this template">e</abbr></a></li></ul></div><div id="File_systems" style="font-size:114%;margin:0 4em"><a href="/wiki/File_system" title="File system">File systems</a></div></th></tr><tr><td class="navbox-abovebelow" colspan="2"><div> <ul><li><a href="/wiki/Comparison_of_file_systems" title="Comparison of file systems">Comparison of file systems</a> <ul><li><a href="/wiki/Comparison_of_distributed_file_systems" title="Comparison of distributed file systems">distributed</a></li></ul></li> <li><a href="/wiki/Unix_filesystem" title="Unix filesystem">Unix filesystem</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Disk and<br />non-rotating</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><td colspan="2" class="navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Advanced_Disc_Filing_System" title="Advanced Disc Filing System">ADFS</a></li> <li><a href="/wiki/AdvFS" title="AdvFS">AdvFS</a></li> <li><a href="/wiki/Amiga_Fast_File_System" title="Amiga Fast File System">Amiga FFS</a></li> <li><a href="/wiki/Amiga_Old_File_System" title="Amiga Old File System">Amiga OFS</a></li> <li><a href="/wiki/Apple_File_System" title="Apple File System">APFS</a></li> <li><a href="/wiki/AtheOS_File_System" class="mw-redirect" title="AtheOS File System">AthFS</a></li> <li><a href="/wiki/Bcachefs" title="Bcachefs">bcachefs</a></li> <li>BFS <ul><li><a href="/wiki/Be_File_System" title="Be File System">Be File System</a></li> <li><a href="/wiki/Boot_File_System" title="Boot File System">Boot File System</a></li> <li>Byte File System (<a href="/wiki/Z/VM" title="Z/VM">z/VM</a>)</li></ul></li> <li><a href="/wiki/Btrfs" title="Btrfs">Btrfs</a></li> <li><a href="/wiki/StorNext_File_System" title="StorNext File System">CVFS</a></li> <li><a href="/wiki/CXFS" title="CXFS">CXFS</a></li> <li><a href="/wiki/Disc_Filing_System" title="Disc Filing System">DFS</a></li> <li>EFS <ul><li><a href="/wiki/Encrypting_File_System" title="Encrypting File System">Encrypting File System</a></li> <li><a href="/wiki/Extent_File_System" title="Extent File System">Extent File System</a></li></ul></li> <li><a href="/wiki/Episode_filesystem" title="Episode filesystem">Episode</a></li> <li><a href="/wiki/Extended_file_system" title="Extended file system">ext</a> <ul><li><a href="/wiki/Ext2" title="Ext2">ext2</a></li> <li><a href="/wiki/Ext3" title="Ext3">ext3</a></li> <li><a href="/wiki/Ext3cow" title="Ext3cow">ext3cow</a></li> <li><a href="/wiki/Ext4" title="Ext4">ext4</a></li></ul></li> <li><a href="/wiki/File_Allocation_Table" title="File Allocation Table">FAT</a> <ul><li><a href="/wiki/ExFAT" title="ExFAT">exFAT</a></li></ul></li> <li><a href="/wiki/Files-11" title="Files-11">Files-11</a></li> <li><a href="/wiki/Fossil_(file_system)" title="Fossil (file system)">Fossil</a></li> <li><a href="/wiki/GPFS" title="GPFS">GPFS</a></li> <li><a href="/wiki/HAMMER_(file_system)" title="HAMMER (file system)">HAMMER</a> <ul><li><a href="/wiki/HAMMER2" title="HAMMER2">HAMMER2</a></li></ul></li> <li><a href="/wiki/Hierarchical_File_System_(Apple)" title="Hierarchical File System (Apple)">HFS</a> (<a href="/wiki/Classic_Mac_OS" title="Classic Mac OS">Classic Mac OS</a>)</li> <li><a href="/wiki/Hierarchical_File_System_(IBM_MVS)" title="Hierarchical File System (IBM MVS)">HFS</a> (<a href="/wiki/MVS" title="MVS">MVS</a>)</li> <li><a href="/wiki/HFS_Plus" title="HFS Plus">HFS+</a></li> <li><a href="/wiki/High_Performance_File_System" title="High Performance File System">HPFS</a></li> <li><a href="/wiki/High_Throughput_File_System" title="High Throughput File System">HTFS</a></li> <li><a href="/wiki/JFS_(file_system)" title="JFS (file system)">JFS</a></li> <li><a href="/wiki/Log-structured_File_System_(BSD)" title="Log-structured File System (BSD)">LFS</a></li> <li>MFS <ul><li><a href="/wiki/Macintosh_File_System" title="Macintosh File System">Macintosh File System</a></li> <li><a href="/wiki/TiVo_Media_File_System" title="TiVo Media File System">TiVo Media File System</a></li></ul></li> <li><a href="/wiki/MINIX_file_system" title="MINIX file system">MINIX</a></li> <li><a href="/wiki/NetWare_File_System" title="NetWare File System">NetWare File System</a></li> <li><a href="/wiki/Next3" title="Next3">Next3</a></li> <li><a href="/wiki/NILFS" title="NILFS">NILFS</a> <ul><li><a href="/wiki/NILFS" title="NILFS">NILFS2</a></li></ul></li> <li><a href="/wiki/Novell_Storage_Services" title="Novell Storage Services">NSS</a></li> <li><a href="/wiki/NTFS" title="NTFS">NTFS</a></li> <li><a href="/wiki/OneFS_distributed_file_system" title="OneFS distributed file system">OneFS</a></li> <li><a href="/wiki/OpenZFS" title="OpenZFS">OpenZFS</a></li> <li><a href="/wiki/Professional_File_System" title="Professional File System">PFS</a></li> <li><a href="/wiki/QFS" title="QFS">QFS</a></li> <li><a href="/wiki/QNX4FS" title="QNX4FS">QNX4FS</a></li> <li><a href="/wiki/ReFS" title="ReFS">ReFS</a></li> <li><a href="/wiki/ReiserFS" title="ReiserFS">ReiserFS</a> <ul><li><a href="/wiki/Reiser4" title="Reiser4">Reiser4</a></li></ul></li> <li><a href="/wiki/Datalight#Reliance_family" title="Datalight">Reliance</a></li> <li><a href="/wiki/Datalight#Reliance_Nitro" title="Datalight">Reliance Nitro</a></li> <li><a href="/wiki/Remote_File_Sharing" title="Remote File Sharing">RFS</a></li> <li>SFS <ul><li>Shared File System (<a href="/wiki/VM_(operating_system)" title="VM (operating system)">VM</a>)</li> <li><a href="/wiki/Smart_File_System" title="Smart File System">Smart File System</a></li></ul></li> <li><a href="/wiki/StorNext_File_System" title="StorNext File System">SNFS</a></li> <li><a href="/wiki/Soup_(Apple)" title="Soup (Apple)">Soup (Apple)</a></li> <li><a href="/wiki/Tux3" title="Tux3">Tux3</a></li> <li><a href="/wiki/UBIFS" title="UBIFS">UBIFS</a></li> <li><a href="/wiki/Unix_File_System" title="Unix File System">UFS/UFS2</a> <ul><li><a href="/wiki/Soft_updates" title="Soft updates">soft updates</a></li> <li><a href="/wiki/Write_Ahead_Physical_Block_Logging" title="Write Ahead Physical Block Logging">WAPBL</a></li></ul></li> <li><a href="/wiki/Veritas_File_System" title="Veritas File System">VxFS</a></li> <li><a href="/wiki/Write_Anywhere_File_Layout" title="Write Anywhere File Layout">WAFL</a></li> <li><a href="/wiki/Xiafs" title="Xiafs">Xiafs</a></li> <li><a href="/wiki/XFS" title="XFS">XFS</a></li> <li><a href="/wiki/Xsan" title="Xsan">Xsan</a></li> <li><a href="/wiki/ZFS_(z/OS_file_system)" title="ZFS (z/OS file system)">zFS</a> (<a href="/wiki/Z/OS" title="Z/OS">z/OS</a>)</li> <li><a href="/wiki/ZFS" title="ZFS">ZFS</a> (<a href="/wiki/Sun_Microsystems" title="Sun Microsystems">Sun</a>)</li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Optical_disc" title="Optical disc">Optical disc</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/High_Sierra_Format" class="mw-redirect" title="High Sierra Format">HSF</a></li> <li><a href="/wiki/ISO_9660" title="ISO 9660">ISO 9660</a></li> <li><a href="/wiki/ISO_13490" title="ISO 13490">ISO 13490</a></li> <li><a href="/wiki/Universal_Disk_Format" title="Universal Disk Format">UDF</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Flash_memory" title="Flash memory">Flash memory</a> and <a href="/wiki/Solid-state_drive" title="Solid-state drive">SSD</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Apple_File_System" title="Apple File System">APFS</a></li> <li><a href="/wiki/File_Allocation_Table" title="File Allocation Table">FAT</a></li> <li><a href="/wiki/ExFAT" title="ExFAT">exFAT</a></li> <li><a href="/wiki/Transaction-Safe_FAT_File_System" title="Transaction-Safe FAT File System">TFAT</a></li> <li><a href="/wiki/EROFS" title="EROFS">EROFS</a></li> <li><a href="/wiki/F2FS" title="F2FS">F2FS</a></li> <li><a href="/wiki/JFS_(file_system)" title="JFS (file system)">JFS</a></li> <li><a href="/wiki/Non-Volatile_File_System" title="Non-Volatile File System">NVFS</a></li></ul> </div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th id="host-side_wear_leveling" scope="row" class="navbox-group" style="width:1%">host-side <a href="/wiki/Wear_leveling" title="Wear leveling">wear leveling</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/CHFS" title="CHFS">CHFS</a></li> <li><a href="/wiki/JFFS" title="JFFS">JFFS</a></li> <li><a href="/wiki/JFFS2" title="JFFS2">JFFS2</a></li> <li><a href="/wiki/LogFS" title="LogFS">LogFS</a></li> <li><a href="/wiki/NILFS" title="NILFS">NILFS</a> <ul><li><a href="/wiki/NILFS" title="NILFS">NILFS2</a></li></ul></li> <li><a href="/wiki/YAFFS" title="YAFFS">YAFFS</a></li> <li><a href="/wiki/UBIFS" title="UBIFS">UBIFS</a></li></ul> </div></td></tr></tbody></table><div> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Clustered_file_system#Distributed_file_systems" title="Clustered file system">Distributed parallel</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/BeeGFS" title="BeeGFS">BeeGFS</a></li> <li><a href="/wiki/Ceph_(software)" title="Ceph (software)">Ceph</a></li> <li><a href="/wiki/CXFS" title="CXFS">CXFS</a></li> <li><a href="/wiki/GFS2" title="GFS2">GFS2</a></li> <li><a href="/wiki/Google_File_System" title="Google File System">Google File System</a></li> <li><a href="/wiki/OCFS2" title="OCFS2">OCFS2</a></li> <li><a href="/wiki/OrangeFS" title="OrangeFS">OrangeFS</a></li> <li><a href="/wiki/Parallel_Virtual_File_System" title="Parallel Virtual File System">PVFS</a></li> <li><a href="/wiki/Quantcast_File_System" title="Quantcast File System">QFS</a></li> <li><a href="/wiki/Xsan" title="Xsan">Xsan</a></li> <li><i><a href="/wiki/List_of_file_systems#Distributed_parallel_file_systems" title="List of file systems">more...</a></i></li></ul> </div></td></tr></tbody></table><div></div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Network-attached_storage" title="Network-attached storage">NAS</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/9P_(protocol)" title="9P (protocol)">9P</a></li> <li><a href="/wiki/Andrew_File_System" title="Andrew File System">AFS</a> (<a href="/wiki/OpenAFS" title="OpenAFS">OpenAFS</a>)</li> <li><a href="/wiki/Apple_Filing_Protocol" title="Apple Filing Protocol">AFP</a></li> <li><a href="/wiki/Coda_(file_system)" title="Coda (file system)">Coda</a></li> <li><a href="/wiki/Distributed_File_System_(Microsoft)" title="Distributed File System (Microsoft)">DFS</a></li> <li><a href="/wiki/Google_File_System" title="Google File System">Google File System</a></li> <li><a href="/wiki/GPFS" title="GPFS">GPFS</a></li> <li><a href="/wiki/Lustre_(file_system)" title="Lustre (file system)">Lustre</a></li> <li><a href="/wiki/NetWare_Core_Protocol" title="NetWare Core Protocol">NCP</a></li> <li><a href="/wiki/Network_File_System" title="Network File System">NFS</a></li> <li><a href="/wiki/Elliptics" title="Elliptics">POHMELFS</a></li> <li><a href="/wiki/Apache_Hadoop" title="Apache Hadoop">Hadoop</a></li> <li><a href="/wiki/Server_Message_Block" title="Server Message Block">SMB (CIFS)</a></li> <li><a href="/wiki/SSHFS" title="SSHFS">SSHFS</a></li> <li><i><a href="/wiki/List_of_file_systems#Distributed_file_systems" title="List of file systems">more...</a></i></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Specialized</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><td colspan="2" class="navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Aufs" title="Aufs">Aufs</a></li> <li><a href="/wiki/AXFS" title="AXFS">AXFS</a></li> <li><a href="/wiki/Boot_File_System" title="Boot File System">Boot File System</a></li> <li><a href="/wiki/CDfs" title="CDfs">CDfs</a></li> <li><a href="/wiki/Compact_Disc_File_System" title="Compact Disc File System">Compact Disc File System</a></li> <li><a href="/wiki/Cramfs" title="Cramfs">cramfs</a></li> <li><a href="/wiki/Davfs2" title="Davfs2">Davfs2</a></li> <li><a href="/wiki/EROFS" title="EROFS">EROFS</a></li> <li><a href="/wiki/FTPFS" title="FTPFS">FTPFS</a></li> <li><a href="/wiki/Filesystem_in_Userspace" title="Filesystem in Userspace">FUSE</a></li> <li><a href="/wiki/Lnfs" title="Lnfs">Lnfs</a></li> <li><a href="/wiki/Linear_Tape_File_System" title="Linear Tape File System">LTFS</a></li> <li><a href="/wiki/NOVA_(filesystem)" title="NOVA (filesystem)">NOVA</a></li> <li><a href="/wiki/Rational_MultiVersion_File_System" class="mw-redirect" title="Rational MultiVersion File System">MVFS</a></li> <li><a href="/wiki/SquashFS" title="SquashFS">SquashFS</a></li> <li><a href="/wiki/FAT_filesystem_and_Linux" title="FAT filesystem and Linux">UMSDOS</a></li> <li><a href="/wiki/OverlayFS" title="OverlayFS">OverlayFS</a></li> <li><a href="/wiki/UnionFS" title="UnionFS">UnionFS</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Pseudo</th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Configfs" title="Configfs">configfs</a></li> <li><a href="/wiki/Device_file" title="Device file">devfs</a></li> <li><a href="/wiki/Debugfs" title="Debugfs">debugfs</a></li> <li><a href="/wiki/Kernfs_(BSD)" title="Kernfs (BSD)">kernfs</a></li> <li><a href="/wiki/Procfs" title="Procfs">procfs</a></li> <li>specfs</li> <li><a href="/wiki/Sysfs" title="Sysfs">sysfs</a></li> <li><a href="/wiki/Tmpfs" title="Tmpfs">tmpfs</a></li> <li><a href="/wiki/WinFS" title="WinFS">WinFS</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Filesystem-level_encryption" title="Filesystem-level encryption">Encrypted</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/ECryptfs" title="ECryptfs">eCryptfs</a></li> <li><a href="/wiki/EncFS" title="EncFS">EncFS</a></li> <li><a href="/wiki/Encrypting_File_System" title="Encrypting File System">EFS</a></li> <li><a href="/wiki/Rubberhose_(file_system)" class="mw-redirect" title="Rubberhose (file system)">Rubberhose</a></li> <li><a href="/wiki/SSHFS" title="SSHFS">SSHFS</a></li> <li><a href="/wiki/Oracle_ZFS" title="Oracle ZFS">ZFS</a></li></ul> </div></td></tr></tbody></table><div></div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Types</th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Clustered_file_system" title="Clustered file system">Clustered</a> <ul><li><a href="/wiki/Global_file_system" title="Global file system">Global</a></li> <li><a href="/wiki/Grid_file_system" title="Grid file system">Grid</a></li> <li><a href="/wiki/Self-certifying_File_System" title="Self-certifying File System">Self-certifying</a></li></ul></li> <li><a href="/wiki/Flash_file_system" title="Flash file system">Flash</a></li> <li><a href="/wiki/Journaling_file_system" title="Journaling file system">Journaling</a></li> <li><a href="/wiki/Log-structured_file_system" title="Log-structured file system">Log-structured</a></li> <li><a href="/wiki/Object_storage" title="Object storage">Object</a></li> <li><a href="/wiki/Record-oriented_filesystem" title="Record-oriented filesystem">Record-oriented</a></li> <li><a href="/wiki/Semantic_file_system" title="Semantic file system">Semantic</a></li> <li><a href="/wiki/Steganographic_file_system" title="Steganographic file system">Steganographic</a></li> <li><a href="/wiki/Synthetic_file_system" title="Synthetic file system">Synthetic</a></li> <li><a href="/wiki/Versioning_file_system" title="Versioning file system">Versioning</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Features</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><td colspan="2" class="navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Case_preservation" title="Case preservation">Case preservation</a></li> <li><a class="mw-selflink selflink">Copy-on-write</a></li> <li><a href="/wiki/Data_deduplication" title="Data deduplication">Data deduplication</a></li> <li><a href="/wiki/Data_scrubbing" title="Data scrubbing">Data scrubbing</a></li> <li><a href="/wiki/Execute_in_place" title="Execute in place">Execute in place</a></li> <li><a href="/wiki/Extent_(file_systems)" title="Extent (file systems)">Extent</a></li> <li><a href="/wiki/File_attribute" title="File attribute">File attribute</a> <ul><li><a href="/wiki/Extended_file_attributes" title="Extended file attributes">Extended file attributes</a></li></ul></li> <li><a href="/wiki/File_change_log" title="File change log">File change log</a></li> <li><a href="/wiki/Fork_(file_system)" title="Fork (file system)">Fork</a></li> <li>Links <ul><li><a href="/wiki/Hard_link" title="Hard link">Hard</a></li> <li><a href="/wiki/Symbolic_link" title="Symbolic link">Symbolic</a></li></ul></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Computer_access_control" title="Computer access control">Access control</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Access-control_list" title="Access-control list">Access-control list</a></li> <li><a href="/wiki/Filesystem-level_encryption" title="Filesystem-level encryption">Filesystem-level encryption</a></li> <li><a href="/wiki/File-system_permissions" title="File-system permissions">Permissions</a> <ul><li><a href="/wiki/Chmod" title="Chmod">Modes</a></li> <li><a href="/wiki/Sticky_bit" title="Sticky bit">Sticky bit</a></li></ul></li></ul> </div></td></tr></tbody></table><div></div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Interface_(computing)" title="Interface (computing)">Interfaces</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/File_manager" title="File manager">File manager</a></li> <li><a href="/wiki/File_system_API" title="File system API">File system API</a> <ul><li><a href="/wiki/Installable_File_System" title="Installable File System">Installable File System</a></li></ul></li> <li><a href="/wiki/Virtual_file_system" title="Virtual file system">Virtual file system</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/List_of_file_systems" title="List of file systems">Lists</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/List_of_cryptographic_file_systems" title="List of cryptographic file systems">Cryptographic</a></li> <li><a href="/wiki/List_of_default_file_systems" title="List of default file systems">Default</a></li> <li><a href="/wiki/List_of_log-structured_file_systems" title="List of log-structured file systems">Log-structured</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Layouts</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Master_Boot_Record" class="mw-redirect" title="Master Boot Record">Master Boot Record</a></li> <li><a href="/wiki/GUID_Partition_Table" title="GUID Partition Table">GUID Partition Table</a></li> <li><a href="/wiki/Apple_Partition_Map" title="Apple Partition Map">Apple Partition Map</a></li></ul> </div></td></tr></tbody></table></div>    </div><noscript><img src="https://login.wikimedia.org/wiki/Special:CentralAutoLogin/start?type=1x1" alt="" width="1" height="1" style="border: none; position: absolute;"></noscript> <div class="printfooter" data-nosnippet="">Retrieved from "<a dir="ltr" href="https://en.wikipedia.org/w/index.php?title=Copy-on-write&oldid=1258225312">https://en.wikipedia.org/w/index.php?title=Copy-on-write&oldid=1258225312</a>"</div></div> <div id="catlinks" class="catlinks" data-mw="interface"><div id="mw-normal-catlinks" class="mw-normal-catlinks"><a href="/wiki/Help:Category" title="Help:Category">Categories</a>: <ul><li><a href="/wiki/Category:Computer_data_storage" title="Category:Computer data storage">Computer data storage</a></li><li><a href="/wiki/Category:Software_optimization" title="Category:Software optimization">Software optimization</a></li><li><a href="/wiki/Category:Virtual_memory" title="Category:Virtual memory">Virtual memory</a></li><li><a href="/wiki/Category:Virtualization" title="Category:Virtualization">Virtualization</a></li></ul></div><div id="mw-hidden-catlinks" class="mw-hidden-catlinks mw-hidden-cats-hidden">Hidden categories: <ul><li><a href="/wiki/Category:CS1_maint:_unfit_URL" title="Category:CS1 maint: unfit URL">CS1 maint: unfit URL</a></li><li><a href="/wiki/Category:Articles_with_short_description" title="Category:Articles with short description">Articles with short description</a></li><li><a href="/wiki/Category:Short_description_is_different_from_Wikidata" title="Category:Short description is different from Wikidata">Short description is different from Wikidata</a></li><li><a href="/wiki/Category:Use_dmy_dates_from_November_2023" title="Category:Use dmy dates from November 2023">Use dmy dates from November 2023</a></li><li><a href="/wiki/Category:All_articles_with_unsourced_statements" title="Category:All articles with unsourced statements">All articles with unsourced statements</a></li><li><a href="/wiki/Category:Articles_with_unsourced_statements_from_November_2023" title="Category:Articles with unsourced statements from November 2023">Articles with unsourced statements from November 2023</a></li><li><a href="/wiki/Category:Articles_to_be_expanded_from_October_2017" title="Category:Articles to be expanded from October 2017">Articles to be expanded from October 2017</a></li><li><a href="/wiki/Category:All_articles_to_be_expanded" title="Category:All articles to be expanded">All articles to be expanded</a></li><li><a href="/wiki/Category:Articles_with_example_C%2B%2B_code" title="Category:Articles with example C++ code">Articles with example C++ code</a></li></ul></div></div> </div> </main> </div> <div class="mw-footer-container"> <footer id="footer" class="mw-footer" > <ul id="footer-info"> <li id="footer-info-lastmod"> This page was last edited on 18 November 2024, at 20:35<span class="anonymous-show"> (UTC)</span>.</li> <li id="footer-info-copyright">Text is available under the <a href="/wiki/Wikipedia:Text_of_the_Creative_Commons_Attribution-ShareAlike_4.0_International_License" title="Wikipedia:Text of the Creative Commons Attribution-ShareAlike 4.0 International License">Creative Commons Attribution-ShareAlike 4.0 License</a>; additional terms may apply. By using this site, you agree to the <a href="https://foundation.wikimedia.org/wiki/Special:MyLanguage/Policy:Terms_of_Use" class="extiw" title="foundation:Special:MyLanguage/Policy:Terms of Use">Terms of Use</a> and <a href="https://foundation.wikimedia.org/wiki/Special:MyLanguage/Policy:Privacy_policy" class="extiw" title="foundation:Special:MyLanguage/Policy:Privacy policy">Privacy Policy</a>. Wikipedia® is a registered trademark of the <a rel="nofollow" class="external text" href="https://wikimediafoundation.org/">Wikimedia Foundation, Inc.</a>, a non-profit organization.</li> </ul> <ul id="footer-places"> <li id="footer-places-privacy"><a href="https://foundation.wikimedia.org/wiki/Special:MyLanguage/Policy:Privacy_policy">Privacy policy</a></li> <li id="footer-places-about"><a href="/wiki/Wikipedia:About">About Wikipedia</a></li> <li id="footer-places-disclaimers"><a href="/wiki/Wikipedia:General_disclaimer">Disclaimers</a></li> <li id="footer-places-contact"><a href="//en.wikipedia.org/wiki/Wikipedia:Contact_us">Contact Wikipedia</a></li> <li id="footer-places-wm-codeofconduct"><a href="https://foundation.wikimedia.org/wiki/Special:MyLanguage/Policy:Universal_Code_of_Conduct">Code of Conduct</a></li> <li id="footer-places-developers"><a href="https://developer.wikimedia.org">Developers</a></li> <li id="footer-places-statslink"><a href="https://stats.wikimedia.org/#/en.wikipedia.org">Statistics</a></li> <li id="footer-places-cookiestatement"><a href="https://foundation.wikimedia.org/wiki/Special:MyLanguage/Policy:Cookie_statement">Cookie statement</a></li> <li id="footer-places-mobileview"><a href="//en.m.wikipedia.org/w/index.php?title=Copy-on-write&mobileaction=toggle_view_mobile" class="noprint stopMobileRedirectToggle">Mobile view</a></li> </ul> <ul id="footer-icons" class="noprint"> <li id="footer-copyrightico"><a href="https://wikimediafoundation.org/" class="cdx-button cdx-button--fake-button cdx-button--size-large cdx-button--fake-button--enabled"><img src="/static/images/footer/wikimedia-button.svg" width="84" height="29" alt="Wikimedia Foundation" loading="lazy"></a></li> <li id="footer-poweredbyico"><a href="https://www.mediawiki.org/" class="cdx-button cdx-button--fake-button cdx-button--size-large cdx-button--fake-button--enabled"><img src="/w/resources/assets/poweredby_mediawiki.svg" alt="Powered by MediaWiki" width="88" height="31" loading="lazy"></a></li> </ul> </footer> </div> </div> </div> <div class="vector-settings" id="p-dock-bottom"> <ul></ul> </div><script>(RLQ=window.RLQ||[]).push(function(){mw.config.set({"wgHostname":"mw-web.codfw.canary-84779d6bf6-psplp","wgBackendResponseTime":167,"wgPageParseReport":{"limitreport":{"cputime":"0.438","walltime":"0.553","ppvisitednodes":{"value":1390,"limit":1000000},"postexpandincludesize":{"value":73732,"limit":2097152},"templateargumentsize":{"value":1560,"limit":2097152},"expansiondepth":{"value":12,"limit":100},"expensivefunctioncount":{"value":5,"limit":500},"unstrip-depth":{"value":1,"limit":20},"unstrip-size":{"value":53991,"limit":5000000},"entityaccesscount":{"value":0,"limit":400},"timingprofile":["100.00% 464.377 1 -total"," 35.32% 164.007 1 Template:Reflist"," 26.73% 124.125 5 Template:Navbox"," 25.82% 119.901 1 Template:File_systems"," 24.53% 113.925 8 Template:Cite_web"," 16.06% 74.596 1 Template:Short_description"," 9.24% 42.899 2 Template:Pagetype"," 8.21% 38.117 1 Template:Expand_section"," 7.62% 35.380 1 Template:Citation_needed"," 7.40% 34.369 1 Template:Ambox"]},"scribunto":{"limitreport-timeusage":{"value":"0.268","limit":"10.000"},"limitreport-memusage":{"value":6034472,"limit":52428800}},"cachereport":{"origin":"mw-web.codfw.main-f69cdc8f6-78s75","timestamp":"20241122143059","ttl":2592000,"transientcontent":false}}});});</script> <script type="application/ld+json">{"@context":"https:\/\/schema.org","@type":"Article","name":"Copy-on-write","url":"https:\/\/en.wikipedia.org\/wiki\/Copy-on-write","sameAs":"http:\/\/www.wikidata.org\/entity\/Q1131607","mainEntity":"http:\/\/www.wikidata.org\/entity\/Q1131607","author":{"@type":"Organization","name":"Contributors to Wikimedia projects"},"publisher":{"@type":"Organization","name":"Wikimedia Foundation, Inc.","logo":{"@type":"ImageObject","url":"https:\/\/www.wikimedia.org\/static\/images\/wmf-hor-googpub.png"}},"datePublished":"2003-12-19T02:39:42Z","dateModified":"2024-11-18T20:35:15Z","headline":"resource-management technique used in computer programming"}</script> </body> </html>