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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="//donate.wikimedia.org/wiki/Special:FundraiserRedirector?utm_source=donate&utm_medium=sidebar&utm_campaign=C13_simple.wikipedia.org&uselang=en"><span>Give to Wikipedia</span></a></li><li id="pt-createaccount" class="user-links-collapsible-item mw-list-item"><a href="/w/index.php?title=Special:CreateAccount&returnto=Cache+%28computing%29" 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=Cache+%28computing%29" title="You are encouraged to log in; however, it is 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 changes 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">Beginning</div> </a> </li> <li id="toc-How_caches_work" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#How_caches_work"> <div class="vector-toc-text"> <span class="vector-toc-numb">1</span> <span>How caches work</span> </div> </a> <button aria-controls="toc-How_caches_work-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 How caches work subsection</span> </button> <ul id="toc-How_caches_work-sublist" class="vector-toc-list"> <li id="toc-Caches_for_reading" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Caches_for_reading"> <div class="vector-toc-text"> <span class="vector-toc-numb">1.1</span> <span>Caches for reading</span> </div> </a> <ul id="toc-Caches_for_reading-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Caches_for_writing" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Caches_for_writing"> <div class="vector-toc-text"> <span class="vector-toc-numb">1.2</span> <span>Caches for writing</span> </div> </a> <ul id="toc-Caches_for_writing-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Selecting_the_entry_to_replace" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Selecting_the_entry_to_replace"> <div class="vector-toc-text"> <span class="vector-toc-numb">2</span> <span>Selecting the entry to replace</span> </div> </a> <ul id="toc-Selecting_the_entry_to_replace-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-History" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#History"> <div class="vector-toc-text"> <span class="vector-toc-numb">3</span> <span>History</span> </div> </a> <ul id="toc-History-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Where_caches_are_used" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Where_caches_are_used"> <div class="vector-toc-text"> <span class="vector-toc-numb">4</span> <span>Where caches are used</span> </div> </a> <button aria-controls="toc-Where_caches_are_used-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 Where caches are used subsection</span> </button> <ul id="toc-Where_caches_are_used-sublist" class="vector-toc-list"> <li id="toc-CPU_caches" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#CPU_caches"> <div class="vector-toc-text"> <span class="vector-toc-numb">4.1</span> <span>CPU caches</span> </div> </a> <ul id="toc-CPU_caches-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Disk_caches" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Disk_caches"> <div class="vector-toc-text"> <span class="vector-toc-numb">4.2</span> <span>Disk caches</span> </div> </a> <ul id="toc-Disk_caches-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Web_caches" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Web_caches"> <div class="vector-toc-text"> <span class="vector-toc-numb">4.3</span> <span>Web caches</span> </div> </a> <ul id="toc-Web_caches-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Caching_with_unreliable_networks" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Caching_with_unreliable_networks"> <div class="vector-toc-text"> <span class="vector-toc-numb">4.4</span> <span>Caching with unreliable networks</span> </div> </a> <ul id="toc-Caching_with_unreliable_networks-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-The_difference_between_buffer_and_cache" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#The_difference_between_buffer_and_cache"> <div class="vector-toc-text"> <span class="vector-toc-numb">5</span> <span>The difference between buffer and cache</span> </div> </a> <ul id="toc-The_difference_between_buffer_and_cache-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">6</span> <span>References</span> </div> </a> <ul id="toc-References-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">Cache (computing)</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 58 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-58" 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">58 languages</span> </label> <div class="vector-dropdown-content"> <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li class="interlanguage-link interwiki-af mw-list-item"><a href="https://af.wikipedia.org/wiki/Kasstelsel" title="Kasstelsel – Afrikaans" lang="af" hreflang="af" data-title="Kasstelsel" data-language-autonym="Afrikaans" data-language-local-name="Afrikaans" class="interlanguage-link-target"><span>Afrikaans</span></a></li><li class="interlanguage-link interwiki-als mw-list-item"><a href="https://als.wikipedia.org/wiki/Cache" title="Cache – Alemannic" lang="gsw" hreflang="gsw" data-title="Cache" data-language-autonym="Alemannisch" data-language-local-name="Alemannic" class="interlanguage-link-target"><span>Alemannisch</span></a></li><li class="interlanguage-link interwiki-ar mw-list-item"><a href="https://ar.wikipedia.org/wiki/%D8%B0%D8%A7%D9%83%D8%B1%D8%A9_%D9%85%D8%AE%D8%A8%D8%A6%D9%8A%D8%A9" title="ذاكرة مخبئية – Arabic" lang="ar" hreflang="ar" data-title="ذاكرة مخبئية" data-language-autonym="العربية" data-language-local-name="Arabic" class="interlanguage-link-target"><span>العربية</span></a></li><li class="interlanguage-link interwiki-az mw-list-item"><a href="https://az.wikipedia.org/wiki/Ke%C5%9F" title="Keş – Azerbaijani" lang="az" hreflang="az" data-title="Keş" data-language-autonym="Azərbaycanca" data-language-local-name="Azerbaijani" class="interlanguage-link-target"><span>Azərbaycanca</span></a></li><li class="interlanguage-link interwiki-bn mw-list-item"><a href="https://bn.wikipedia.org/wiki/%E0%A6%95%E0%A7%8D%E0%A6%AF%E0%A6%BE%E0%A6%B6_(%E0%A6%95%E0%A6%AE%E0%A7%8D%E0%A6%AA%E0%A6%BF%E0%A6%89%E0%A6%9F%E0%A6%BF%E0%A6%82)" title="ক্যাশ (কম্পিউটিং) – Bangla" lang="bn" hreflang="bn" data-title="ক্যাশ (কম্পিউটিং)" data-language-autonym="বাংলা" data-language-local-name="Bangla" class="interlanguage-link-target"><span>বাংলা</span></a></li><li class="interlanguage-link interwiki-bh mw-list-item"><a href="https://bh.wikipedia.org/wiki/%E0%A4%95%E0%A5%88%E0%A4%B6_(%E0%A4%95%E0%A4%82%E0%A4%AA%E0%A5%8D%E0%A4%AF%E0%A5%82%E0%A4%9F%E0%A4%BF%E0%A4%82%E0%A4%97)" title="कैश (कंप्यूटिंग) – Bhojpuri" lang="bh" hreflang="bh" data-title="कैश (कंप्यूटिंग)" data-language-autonym="भोजपुरी" data-language-local-name="Bhojpuri" class="interlanguage-link-target"><span>भोजपुरी</span></a></li><li class="interlanguage-link interwiki-bg mw-list-item"><a href="https://bg.wikipedia.org/wiki/%D0%9A%D0%B5%D1%88%D0%BF%D0%B0%D0%BC%D0%B5%D1%82" title="Кешпамет – Bulgarian" lang="bg" hreflang="bg" data-title="Кешпамет" data-language-autonym="Български" data-language-local-name="Bulgarian" class="interlanguage-link-target"><span>Български</span></a></li><li class="interlanguage-link interwiki-bs mw-list-item"><a href="https://bs.wikipedia.org/wiki/Ke%C5%A1_memorija" title="Keš memorija – Bosnian" lang="bs" hreflang="bs" data-title="Keš memorija" data-language-autonym="Bosanski" data-language-local-name="Bosnian" class="interlanguage-link-target"><span>Bosanski</span></a></li><li class="interlanguage-link interwiki-ca mw-list-item"><a href="https://ca.wikipedia.org/wiki/Mem%C3%B2ria_cau" title="Memòria cau – Catalan" lang="ca" hreflang="ca" data-title="Memòria cau" data-language-autonym="Català" data-language-local-name="Catalan" class="interlanguage-link-target"><span>Català</span></a></li><li class="interlanguage-link interwiki-cs mw-list-item"><a href="https://cs.wikipedia.org/wiki/Cache" title="Cache – Czech" lang="cs" hreflang="cs" data-title="Cache" data-language-autonym="Čeština" data-language-local-name="Czech" class="interlanguage-link-target"><span>Čeština</span></a></li><li class="interlanguage-link interwiki-da mw-list-item"><a href="https://da.wikipedia.org/wiki/Cache" title="Cache – Danish" lang="da" hreflang="da" data-title="Cache" data-language-autonym="Dansk" data-language-local-name="Danish" class="interlanguage-link-target"><span>Dansk</span></a></li><li class="interlanguage-link interwiki-de mw-list-item"><a href="https://de.wikipedia.org/wiki/Cache" title="Cache – German" lang="de" hreflang="de" data-title="Cache" data-language-autonym="Deutsch" data-language-local-name="German" class="interlanguage-link-target"><span>Deutsch</span></a></li><li class="interlanguage-link interwiki-et mw-list-item"><a href="https://et.wikipedia.org/wiki/Vahem%C3%A4lu" title="Vahemälu – Estonian" lang="et" hreflang="et" data-title="Vahemälu" data-language-autonym="Eesti" data-language-local-name="Estonian" class="interlanguage-link-target"><span>Eesti</span></a></li><li class="interlanguage-link interwiki-el mw-list-item"><a href="https://el.wikipedia.org/wiki/%CE%9A%CF%81%CF%85%CF%86%CE%AE_%CE%BC%CE%BD%CE%AE%CE%BC%CE%B7" title="Κρυφή μνήμη – Greek" lang="el" hreflang="el" data-title="Κρυφή μνήμη" data-language-autonym="Ελληνικά" data-language-local-name="Greek" class="interlanguage-link-target"><span>Ελληνικά</span></a></li><li class="interlanguage-link interwiki-en mw-list-item"><a href="https://en.wikipedia.org/wiki/Cache_(computing)" title="Cache (computing) – English" lang="en" hreflang="en" data-title="Cache (computing)" data-language-autonym="English" data-language-local-name="English" class="interlanguage-link-target"><span>English</span></a></li><li class="interlanguage-link interwiki-es mw-list-item"><a href="https://es.wikipedia.org/wiki/Cach%C3%A9_(inform%C3%A1tica)" title="Caché (informática) – Spanish" lang="es" hreflang="es" data-title="Caché (informática)" data-language-autonym="Español" data-language-local-name="Spanish" class="interlanguage-link-target"><span>Español</span></a></li><li class="interlanguage-link interwiki-eo mw-list-item"><a href="https://eo.wikipedia.org/wiki/Ka%C5%9Dmemoro" title="Kaŝmemoro – Esperanto" lang="eo" hreflang="eo" data-title="Kaŝmemoro" data-language-autonym="Esperanto" data-language-local-name="Esperanto" class="interlanguage-link-target"><span>Esperanto</span></a></li><li class="interlanguage-link interwiki-eu mw-list-item"><a href="https://eu.wikipedia.org/wiki/Cache_memoria" title="Cache memoria – Basque" lang="eu" hreflang="eu" data-title="Cache memoria" data-language-autonym="Euskara" data-language-local-name="Basque" class="interlanguage-link-target"><span>Euskara</span></a></li><li class="interlanguage-link interwiki-fa mw-list-item"><a href="https://fa.wikipedia.org/wiki/%D8%AD%D8%A7%D9%81%D8%B8%D9%87_%D9%86%D9%87%D8%A7%D9%86_(%D8%B1%D8%A7%DB%8C%D8%A7%D9%86%D8%B4)" title="حافظه نهان (رایانش) – Persian" lang="fa" hreflang="fa" data-title="حافظه نهان (رایانش)" 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/M%C3%A9moire_cache" title="Mémoire cache – French" lang="fr" hreflang="fr" data-title="Mémoire cache" data-language-autonym="Français" data-language-local-name="French" class="interlanguage-link-target"><span>Français</span></a></li><li class="interlanguage-link interwiki-gl mw-list-item"><a href="https://gl.wikipedia.org/wiki/Cach%C3%A9" title="Caché – Galician" lang="gl" hreflang="gl" data-title="Caché" data-language-autonym="Galego" data-language-local-name="Galician" class="interlanguage-link-target"><span>Galego</span></a></li><li class="interlanguage-link interwiki-ko mw-list-item"><a href="https://ko.wikipedia.org/wiki/%EC%BA%90%EC%8B%9C" title="캐시 – Korean" lang="ko" hreflang="ko" data-title="캐시" 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/Priru%C4%8Dna_memorija" title="Priručna memorija – Croatian" lang="hr" hreflang="hr" data-title="Priručna memorija" data-language-autonym="Hrvatski" data-language-local-name="Croatian" class="interlanguage-link-target"><span>Hrvatski</span></a></li><li class="interlanguage-link interwiki-id mw-list-item"><a href="https://id.wikipedia.org/wiki/Tembolok_(komputer)" title="Tembolok (komputer) – Indonesian" lang="id" hreflang="id" data-title="Tembolok (komputer)" data-language-autonym="Bahasa Indonesia" data-language-local-name="Indonesian" class="interlanguage-link-target"><span>Bahasa Indonesia</span></a></li><li class="interlanguage-link interwiki-ia mw-list-item"><a href="https://ia.wikipedia.org/wiki/Cache" title="Cache – Interlingua" lang="ia" hreflang="ia" data-title="Cache" data-language-autonym="Interlingua" data-language-local-name="Interlingua" class="interlanguage-link-target"><span>Interlingua</span></a></li><li class="interlanguage-link interwiki-is mw-list-item"><a href="https://is.wikipedia.org/wiki/Skyndiminni" title="Skyndiminni – Icelandic" lang="is" hreflang="is" data-title="Skyndiminni" data-language-autonym="Íslenska" data-language-local-name="Icelandic" class="interlanguage-link-target"><span>Íslenska</span></a></li><li class="interlanguage-link interwiki-it mw-list-item"><a href="https://it.wikipedia.org/wiki/Cache" title="Cache – Italian" lang="it" hreflang="it" data-title="Cache" 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%96%D7%99%D7%9B%D7%A8%D7%95%D7%9F_%D7%9E%D7%98%D7%9E%D7%95%D7%9F" title="זיכרון מטמון – Hebrew" lang="he" hreflang="he" data-title="זיכרון מטמון" data-language-autonym="עברית" data-language-local-name="Hebrew" class="interlanguage-link-target"><span>עברית</span></a></li><li class="interlanguage-link interwiki-kk mw-list-item"><a href="https://kk.wikipedia.org/wiki/%D0%9C%D3%99%D0%BB%D1%96%D0%BC%D0%B5%D1%82%D1%82%D0%B5%D1%80_%D0%B1%D2%AF%D1%80%D0%BA%D0%B5%D0%BC%D0%B5%D1%81%D1%96" title="Мәліметтер бүркемесі – Kazakh" lang="kk" hreflang="kk" data-title="Мәліметтер бүркемесі" data-language-autonym="Қазақша" data-language-local-name="Kazakh" class="interlanguage-link-target"><span>Қазақша</span></a></li><li class="interlanguage-link interwiki-sw mw-list-item"><a href="https://sw.wikipedia.org/wiki/Hifadhi_muda" title="Hifadhi muda – Swahili" lang="sw" hreflang="sw" data-title="Hifadhi muda" data-language-autonym="Kiswahili" data-language-local-name="Swahili" class="interlanguage-link-target"><span>Kiswahili</span></a></li><li class="interlanguage-link interwiki-lv mw-list-item"><a href="https://lv.wikipedia.org/wiki/Ke%C5%A1atmi%C5%86a" title="Kešatmiņa – Latvian" lang="lv" hreflang="lv" data-title="Kešatmiņa" data-language-autonym="Latviešu" data-language-local-name="Latvian" class="interlanguage-link-target"><span>Latviešu</span></a></li><li class="interlanguage-link interwiki-lt mw-list-item"><a href="https://lt.wikipedia.org/wiki/Pod%C4%97liavimas" title="Podėliavimas – Lithuanian" lang="lt" hreflang="lt" data-title="Podėliavimas" data-language-autonym="Lietuvių" data-language-local-name="Lithuanian" class="interlanguage-link-target"><span>Lietuvių</span></a></li><li class="interlanguage-link interwiki-hu mw-list-item"><a href="https://hu.wikipedia.org/wiki/Gyors%C3%ADt%C3%B3t%C3%A1r" title="Gyorsítótár – Hungarian" lang="hu" hreflang="hu" data-title="Gyorsítótár" data-language-autonym="Magyar" data-language-local-name="Hungarian" class="interlanguage-link-target"><span>Magyar</span></a></li><li class="interlanguage-link interwiki-mr mw-list-item"><a href="https://mr.wikipedia.org/wiki/%E0%A4%B8%E0%A4%AF" title="सय – Marathi" lang="mr" hreflang="mr" data-title="सय" data-language-autonym="मराठी" data-language-local-name="Marathi" class="interlanguage-link-target"><span>मराठी</span></a></li><li class="interlanguage-link interwiki-ms mw-list-item"><a href="https://ms.wikipedia.org/wiki/Cache" title="Cache – Malay" lang="ms" hreflang="ms" data-title="Cache" data-language-autonym="Bahasa Melayu" data-language-local-name="Malay" class="interlanguage-link-target"><span>Bahasa Melayu</span></a></li><li class="interlanguage-link interwiki-mn mw-list-item"><a href="https://mn.wikipedia.org/wiki/Cache" title="Cache – Mongolian" lang="mn" hreflang="mn" data-title="Cache" data-language-autonym="Монгол" data-language-local-name="Mongolian" class="interlanguage-link-target"><span>Монгол</span></a></li><li class="interlanguage-link interwiki-nl mw-list-item"><a href="https://nl.wikipedia.org/wiki/Cache_(tijdelijk_geheugen)" title="Cache (tijdelijk geheugen) – Dutch" lang="nl" hreflang="nl" data-title="Cache (tijdelijk geheugen)" data-language-autonym="Nederlands" data-language-local-name="Dutch" class="interlanguage-link-target"><span>Nederlands</span></a></li><li class="interlanguage-link interwiki-ja mw-list-item"><a href="https://ja.wikipedia.org/wiki/%E3%82%AD%E3%83%A3%E3%83%83%E3%82%B7%E3%83%A5_(%E3%82%B3%E3%83%B3%E3%83%94%E3%83%A5%E3%83%BC%E3%82%BF%E3%82%B7%E3%82%B9%E3%83%86%E3%83%A0)" title="キャッシュ (コンピュータシステム) – Japanese" lang="ja" hreflang="ja" data-title="キャッシュ (コンピュータシステム)" 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-mhr mw-list-item"><a href="https://mhr.wikipedia.org/wiki/%D0%9A%D0%AD%D0%A8-%D1%88%D0%B0%D1%80%D0%BD%D1%8B%D1%88" title="КЭШ-шарныш – Eastern Mari" lang="mhr" hreflang="mhr" data-title="КЭШ-шарныш" data-language-autonym="Олык марий" data-language-local-name="Eastern Mari" class="interlanguage-link-target"><span>Олык марий</span></a></li><li class="interlanguage-link interwiki-pap mw-list-item"><a href="https://pap.wikipedia.org/wiki/Cache" title="Cache – Papiamento" lang="pap" hreflang="pap" data-title="Cache" data-language-autonym="Papiamentu" data-language-local-name="Papiamento" class="interlanguage-link-target"><span>Papiamentu</span></a></li><li class="interlanguage-link interwiki-pl mw-list-item"><a href="https://pl.wikipedia.org/wiki/Pami%C4%99%C4%87_podr%C4%99czna" title="Pamięć podręczna – Polish" lang="pl" hreflang="pl" data-title="Pamięć podręczna" 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/Cache" title="Cache – Portuguese" lang="pt" hreflang="pt" data-title="Cache" data-language-autonym="Português" data-language-local-name="Portuguese" class="interlanguage-link-target"><span>Português</span></a></li><li class="interlanguage-link interwiki-ro mw-list-item"><a href="https://ro.wikipedia.org/wiki/Memorie_cache" title="Memorie cache – Romanian" lang="ro" hreflang="ro" data-title="Memorie cache" data-language-autonym="Română" data-language-local-name="Romanian" class="interlanguage-link-target"><span>Română</span></a></li><li class="interlanguage-link interwiki-ru mw-list-item"><a href="https://ru.wikipedia.org/wiki/%D0%9A%D1%8D%D1%88" title="Кэш – Russian" lang="ru" hreflang="ru" data-title="Кэш" data-language-autonym="Русский" data-language-local-name="Russian" class="interlanguage-link-target"><span>Русский</span></a></li><li class="interlanguage-link interwiki-sq mw-list-item"><a href="https://sq.wikipedia.org/wiki/Cache" title="Cache – Albanian" lang="sq" hreflang="sq" data-title="Cache" data-language-autonym="Shqip" data-language-local-name="Albanian" class="interlanguage-link-target"><span>Shqip</span></a></li><li class="interlanguage-link interwiki-sk mw-list-item"><a href="https://sk.wikipedia.org/wiki/R%C3%BDchla_vyrovn%C3%A1vacia_pam%C3%A4%C5%A5" title="Rýchla vyrovnávacia pamäť – Slovak" lang="sk" hreflang="sk" data-title="Rýchla vyrovnávacia pamäť" data-language-autonym="Slovenčina" data-language-local-name="Slovak" class="interlanguage-link-target"><span>Slovenčina</span></a></li><li class="interlanguage-link interwiki-sr mw-list-item"><a href="https://sr.wikipedia.org/wiki/%D0%9A%D0%B5%D1%88_%D0%BC%D0%B5%D0%BC%D0%BE%D1%80%D0%B8%D1%98%D0%B0" title="Кеш меморија – Serbian" lang="sr" hreflang="sr" data-title="Кеш меморија" data-language-autonym="Српски / srpski" data-language-local-name="Serbian" class="interlanguage-link-target"><span>Српски / srpski</span></a></li><li class="interlanguage-link interwiki-su mw-list-item"><a href="https://su.wikipedia.org/wiki/Sindangan" title="Sindangan – Sundanese" lang="su" hreflang="su" data-title="Sindangan" data-language-autonym="Sunda" data-language-local-name="Sundanese" class="interlanguage-link-target"><span>Sunda</span></a></li><li class="interlanguage-link interwiki-fi mw-list-item"><a href="https://fi.wikipedia.org/wiki/V%C3%A4limuisti" title="Välimuisti – Finnish" lang="fi" hreflang="fi" data-title="Välimuisti" data-language-autonym="Suomi" data-language-local-name="Finnish" class="interlanguage-link-target"><span>Suomi</span></a></li><li class="interlanguage-link interwiki-sv mw-list-item"><a href="https://sv.wikipedia.org/wiki/Cache" title="Cache – Swedish" lang="sv" hreflang="sv" data-title="Cache" data-language-autonym="Svenska" data-language-local-name="Swedish" class="interlanguage-link-target"><span>Svenska</span></a></li><li class="interlanguage-link interwiki-th mw-list-item"><a href="https://th.wikipedia.org/wiki/%E0%B9%81%E0%B8%84%E0%B8%8A" title="แคช – Thai" lang="th" hreflang="th" data-title="แคช" data-language-autonym="ไทย" data-language-local-name="Thai" class="interlanguage-link-target"><span>ไทย</span></a></li><li class="interlanguage-link interwiki-tr mw-list-item"><a href="https://tr.wikipedia.org/wiki/%C3%96nbellek" title="Önbellek – Turkish" lang="tr" hreflang="tr" data-title="Önbellek" 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%B5%D1%88" title="Кеш – Ukrainian" lang="uk" hreflang="uk" data-title="Кеш" data-language-autonym="Українська" data-language-local-name="Ukrainian" class="interlanguage-link-target"><span>Українська</span></a></li><li class="interlanguage-link interwiki-ur mw-list-item"><a href="https://ur.wikipedia.org/wiki/%DA%A9%DB%8C%D8%B4%DB%92_(%DA%A9%D9%85%D9%BE%DB%8C%D9%88%D9%B9%D9%86%DA%AF)" title="کیشے (کمپیوٹنگ) – Urdu" lang="ur" hreflang="ur" data-title="کیشے (کمپیوٹنگ)" data-language-autonym="اردو" 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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 Simple English Wikipedia, the free encyclopedia</div> </div> <div id="contentSub"><div id="mw-content-subtitle"><span class="mw-redirectedfrom">(Redirected from <a href="/w/index.php?title=Cache&redirect=no" class="mw-redirect" title="Cache">Cache</a>)</span></div></div> <div id="mw-content-text" class="mw-body-content"><div class="mw-content-ltr mw-parser-output" lang="en" dir="ltr"><p><b>Caching</b> is a term used in <a href="/wiki/Computer_science" title="Computer science">computer science</a>. The idea behind a <b>cache</b> (<a href="/wiki/IPA" class="mw-redirect" title="IPA">pronounced</a> "cash" <span class="rt-commentedText nowrap"><span class="IPA nopopups noexcerpt"><a href="/wiki/Help:IPA/English" title="Help:IPA/English">/<span style="border-bottom:1px dotted"><span title="/ˈ/: primary stress follows">ˈ</span><span title="'k' in 'kind'">k</span><span title="/æ/: 'a' in 'bad'">æ</span><span title="/ʃ/: 'sh' in 'shy'">ʃ</span></span>/</a></span></span> <a href="/wiki/Help:Pronunciation_respelling_key" title="Help:Pronunciation respelling key"><i title="English pronunciation respelling"><span style="font-size:90%">KASH</span></i></a> <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><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><sup id="cite_ref-3" class="reference"><a href="#cite_note-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup>) is very simple: Very often, obtaining a result for a calculation is very time-consuming, so storing the result is generally a good idea. Two kinds of <a href="/wiki/Data_storage_device" title="Data storage device">storage media</a> are used: One is usually quite big, but accessing it is "slow"; the other one can be accessed much faster, but generally it is small. The very basic idea behind caching is to use the medium that is fast to access to have copies of <a href="/wiki/Information" title="Information">data</a>. There is no difference between the copy, and the original. Accessing the original data may take a long time, or it may be expensive to do (for example: the results of a difficult problem that take a long time to solve). For this reason, it is much "cheaper" to simply use the copy of the data from the cache. Put differently, a cache is a temporary storage area that has copies of data that is used often. When a copy of the data is in this cache, it is faster to use this copy rather than re-fetching or re-calculating the original data. This will make the average time needed to access the data shorter. Putting a new value into a cache often means that an older value needs to be replaced. There are different ideas (usually called "strategies") on how to select the value to replace. </p><p>A <a href="/w/index.php?title=Buffer&action=edit&redlink=1" class="new" title="Buffer (not yet started)">buffer</a> is very similar to a cache. It is different in that the client accessing the data in a buffer knows there is a buffer; the buffer is managed by the application. With a cache, the client accessing the data need not be aware there is a cache. </p><p>Typical computer applications access data in very similar ways. Suppose the data is structured into "blocks", which can be accessed individually. When an application accesses a block it is also very likely to access (or reference) a block that is "close" to the original block. This is known as <a href="/wiki/Locality_of_reference" title="Locality of reference">locality of reference</a>. There are different kinds of such "locality". Locality of reference is one of the reasons why caches work well in many areas of computing. </p><p>In order to work well, caches are small, compared to the whole amount of data. The bigger the cache, the longer it takes to lookup an entry. Bigger caches are also more expensive to build. </p> <meta property="mw:PageProp/toc" /> <div class="mw-heading mw-heading2"><h2 id="How_caches_work">How caches work</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Cache_(computing)&veaction=edit&section=1" title="Change section: How caches work" class="mw-editsection-visualeditor"><span>change</span></a><span class="mw-editsection-divider"> | </span><a href="/w/index.php?title=Cache_(computing)&action=edit&section=1" title="Edit section's source code: How caches work"><span>change source</span></a><span class="mw-editsection-bracket">]</span></span></div> <figure typeof="mw:File/Frame"><a href="/wiki/File:Cache,basic.svg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/3/3d/Cache%2Cbasic.svg/320px-Cache%2Cbasic.svg.png" decoding="async" width="320" height="140" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/3/3d/Cache%2Cbasic.svg/480px-Cache%2Cbasic.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/3/3d/Cache%2Cbasic.svg/640px-Cache%2Cbasic.svg.png 2x" data-file-width="320" data-file-height="140" /></a><figcaption>Diagram of a CPU memory cache</figcaption></figure> <p>A cache is a block of memory for storing data which is likely used again. The <a href="/wiki/CPU" class="mw-redirect" title="CPU">CPU</a> and <a href="/wiki/Hard_drive" class="mw-redirect" title="Hard drive">hard drive</a> often use a cache, as do <a href="/wiki/Web_browser" title="Web browser">web browsers</a> and <a href="/wiki/Server" title="Server">web servers</a>. </p><p>A cache is made up of many entries, called a <i>pool</i>. Each entry holds a datum (a bit of <a href="/wiki/Information" title="Information">data</a>) which is a copy of a datum in another place. Caches usually use what is called a <i>backing store</i>. Backing stores are slow or expensive to access, compared to the cache. A disk cache uses a <a href="/wiki/Hard_disk" title="Hard disk">hard disk</a> as a backing store, for example. Each entry also has a little information attached, called a <i>tag</i>. This tag is used to find the location where the original data is stored. </p> <div class="mw-heading mw-heading3"><h3 id="Caches_for_reading">Caches for reading</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Cache_(computing)&veaction=edit&section=2" title="Change section: Caches for reading" class="mw-editsection-visualeditor"><span>change</span></a><span class="mw-editsection-divider"> | </span><a href="/w/index.php?title=Cache_(computing)&action=edit&section=2" title="Edit section's source code: Caches for reading"><span>change source</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>A client (a CPU, web browser, <a href="/wiki/Operating_system" title="Operating system">operating system</a>) wants to access a bit of data, it believes to be in the backing store, it first checks to see if the datum can be found in the cache. If the data can be found in the cache, the client can use it and does not need to use the main memory. This is known as a <b>cache hit</b>.<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> So, for example, a web browser program might check its local cache on disk to see if it has a local copy of the contents of a web page at a particular <a href="/wiki/URL" class="mw-redirect" title="URL">URL</a>. In this example, the URL is the tag, and the contents of the web page is the datum. </p><p>The other situation that can occur is that the datum with the tag cannot be found in the cache. This is known as <b>cache miss</b>. The datum needs to be fetched from the backing store. Usually, it is copied into the cache, so that the next time, it no longer needs to be fetched from the backing store. </p><p>The cache only has a limited size. To make room for the previously uncached entry, another cached entry may need to be deleted from the cache. Special <a href="/wiki/Rule" class="mw-disambig" title="Rule">rules</a> are used to find the entry that should best be deleted. These rules are usually called <a href="/wiki/Heuristics" class="mw-redirect" title="Heuristics">Heuristics</a>. Heuristics used to find the entry are called <a href="/wiki/Page_replacement_algorithm" title="Page replacement algorithm">replacement policy</a>. A very simple rule used is called <i>Least recently used</i> (or <a href="/w/index.php?title=LRU&action=edit&redlink=1" class="new" title="LRU (not yet started)">LRU</a>). It simply takes the entry that was used the longest time ago. Other heuristics are listed at <a href="/wiki/Cache_algorithm" title="Cache algorithm">cache algorithm</a>.. </p> <div class="mw-heading mw-heading3"><h3 id="Caches_for_writing">Caches for writing</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Cache_(computing)&veaction=edit&section=3" title="Change section: Caches for writing" class="mw-editsection-visualeditor"><span>change</span></a><span class="mw-editsection-divider"> | </span><a href="/w/index.php?title=Cache_(computing)&action=edit&section=3" title="Edit section's source code: Caches for writing"><span>change source</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Caches can also be used for writing data; the benefit of this is that the client can continue its operation once the entry has been written to the cache; it does not have to wait until the entry is written to the backing store. </p><p>However, the entry must be written to the backing store at some point in time. The timing when this happens is controlled by the <b>write policy</b>. </p><p>In a <b>write-through</b> cache, each entry is written to the backing store immediately, as well as being stored in cache. </p><p>The other option is to only write to cache, and write to the backing store later. This is known as <b>write-back</b> (or <b> write-behind</b>) cache. The cache marks the entries that have not yet been written to the backing store; the mark that is used is often referred to as <b>dirty</b> flag. Before the entries are deleted from the cache, they are written to the backing store. This is known as <b>lazy write</b>. A miss in a write-back cache (which requires a block to be replaced by another) will often need two memory accesses: one to get the needed datum, and another to write replaced data from the cache to the store. </p><p>The caching policy may also say that a certain datum must be written to cache. The client may have made many changes to the datum in the cache. After it is done, it may explicitly tell the cache to write back the datum. </p><p><b>No-write allocation</b> is a cache policy where only reads are cached. This avoids the need for write-back or write-through caching. Writes are done to the backing store all the time. </p><p>The client is not the application that changes data in the backing store. If the data changed in the backing store, the copy in the cache will be out of date, or <i>stale</i>. Alternatively, when the client updates the data in the cache, copies of that data in other caches will become stale. There are special communication <a href="/wiki/Protocol" class="mw-redirect" title="Protocol">protocols</a> that allow cache managers to talk to each other to keep the data meaningful. These are known as <a href="/wiki/Cache_coherency" class="mw-redirect" title="Cache coherency">coherency protocols</a>. </p> <div class="mw-heading mw-heading2"><h2 id="Selecting_the_entry_to_replace">Selecting the entry to replace</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Cache_(computing)&veaction=edit&section=4" title="Change section: Selecting the entry to replace" class="mw-editsection-visualeditor"><span>change</span></a><span class="mw-editsection-divider"> | </span><a href="/w/index.php?title=Cache_(computing)&action=edit&section=4" title="Edit section's source code: Selecting the entry to replace"><span>change source</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>A cache is small, and it will be full, or almost full, most of the time. So when a new value is added, an old one needs to be removed. There are different ways in which this selection can be done: </p> <ul><li>First in First out: Simply replace the entry that was added to the cache the longest time ago</li> <li>Least recently used: This idea is similar to the FIFO above, but when an entry is used, its timestamp/age is updated.</li> <li>Least frequently used: Again, similar to the FIFO case, instead of using a timestamp use a counter, which is incremented each time an entry is used</li> <li>Pick an entry at random</li></ul> <div class="mw-heading mw-heading2"><h2 id="History">History</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Cache_(computing)&veaction=edit&section=5" title="Change section: History" class="mw-editsection-visualeditor"><span>change</span></a><span class="mw-editsection-divider"> | </span><a href="/w/index.php?title=Cache_(computing)&action=edit&section=5" title="Edit section's source code: History"><span>change source</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The word <i>cache</i> was first used in computing in 1967, when a scientific article was prepared to be published in IBM Systems Journal. The article was about a new improvement of the memory in Model 85. Model 85 was a computer of the IBM System/360 product line. The editor of the Journal wanted a better word for <i>high-speed buffer</i>, used in the article. He got no input, and suggested <i>cache</i>, from the <a href="/wiki/French_language" title="French language">French</a> <i>cacher</i>, meaning "to hide". The article was published in early 1968, and the authors were honored by IBM. Their work was widely welcomed and improved. <i>Cache</i> soon became standard usage in computer literature.<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="Where_caches_are_used">Where caches are used</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Cache_(computing)&veaction=edit&section=6" title="Change section: Where caches are used" class="mw-editsection-visualeditor"><span>change</span></a><span class="mw-editsection-divider"> | </span><a href="/w/index.php?title=Cache_(computing)&action=edit&section=6" title="Edit section's source code: Where caches are used"><span>change source</span></a><span class="mw-editsection-bracket">]</span></span></div> <div class="mw-heading mw-heading3"><h3 id="CPU_caches">CPU caches</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Cache_(computing)&veaction=edit&section=7" title="Change section: CPU caches" class="mw-editsection-visualeditor"><span>change</span></a><span class="mw-editsection-divider"> | </span><a href="/w/index.php?title=Cache_(computing)&action=edit&section=7" title="Edit section's source code: CPU caches"><span>change source</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Small memories on or close to the <a href="/wiki/Microprocessor" title="Microprocessor">CPU chip</a> can be made faster than the much larger <a href="/wiki/RAM" class="mw-redirect" title="RAM">main memory</a>. Most CPUs since the 1980s have used one or more caches. Modern general-purpose CPUs inside <a href="/wiki/Personal_computer" title="Personal computer">personal computers</a> may have as many as half a dozen. Each cache may be specialised to a different part of the task of executing programs. </p> <div class="mw-heading mw-heading3"><h3 id="Disk_caches">Disk caches</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Cache_(computing)&veaction=edit&section=8" title="Change section: Disk caches" class="mw-editsection-visualeditor"><span>change</span></a><span class="mw-editsection-divider"> | </span><a href="/w/index.php?title=Cache_(computing)&action=edit&section=8" title="Edit section's source code: Disk caches"><span>change source</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>CPU caches are generally managed entirely by <a href="/wiki/Computer_hardware" title="Computer hardware">hardware</a>, other caches are managed by a different kinds of <a href="/wiki/Software" title="Software">software</a>. The operating system usually manages a <i><a href="/wiki/Page_cache" title="Page cache">page cache</a></i> in main memory. Users outside computer science usually call this cache <a href="/wiki/Virtual_memory" title="Virtual memory">virtual memory</a>. It is managed by the <a href="/wiki/Kernel_(computer_science)" title="Kernel (computer science)">kernel</a> of the operating system. </p><p>Modern hard drives have <a href="/wiki/Disk_buffer" title="Disk buffer">disk buffers</a>. These are sometimes called "disk cache", but this is wrong. The main function of these buffers is to order disk writes, and to manage reads. Repeated cache hits are rare, because the buffer is very small compared to the size of the hard drive. </p><p>Local hard disks are fast compared to other storage devices, such as remote servers, local <a href="/wiki/Tape_drive" title="Tape drive">tape drives</a>, or <a href="/w/index.php?title=Optical_jukebox&action=edit&redlink=1" class="new" title="Optical jukebox (not yet started)">optical jukeboxes</a>. Using local hard disks as caches is the main concept of <a href="/w/index.php?title=Hierarchical_storage_management&action=edit&redlink=1" class="new" title="Hierarchical storage management (not yet started)">hierarchical storage management</a>. </p> <div class="mw-heading mw-heading3"><h3 id="Web_caches">Web caches</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Cache_(computing)&veaction=edit&section=9" title="Change section: Web caches" class="mw-editsection-visualeditor"><span>change</span></a><span class="mw-editsection-divider"> | </span><a href="/w/index.php?title=Cache_(computing)&action=edit&section=9" title="Edit section's source code: Web caches"><span>change source</span></a><span class="mw-editsection-bracket">]</span></span></div> <p><a href="/wiki/Web_browser" title="Web browser">Web browsers</a> and <a href="/wiki/Proxy_server" title="Proxy server">web proxy servers</a> use caches to store previous responses from <a href="/wiki/Server" title="Server">web servers</a>, such as <a href="/wiki/Web_page" class="mw-redirect" title="Web page">web pages</a>. Web caches reduce the amount of information that needs to be transmitted over the network. Information previously stored in the cache can often be re-used. This reduces <a href="/wiki/Bandwidth_(computing)" title="Bandwidth (computing)">bandwidth</a> and processing requirements of the web server, and helps to improve <a href="/w/index.php?title=Responsiveness&action=edit&redlink=1" class="new" title="Responsiveness (not yet started)">responsiveness</a> for users of the web. </p><p>Modern web browsers use a built-in web cache, but some <a href="/wiki/Internet_service_provider" title="Internet service provider">internet service providers</a> or organizations also use a caching proxy server. This is a web cache that is shared between all users of that network. </p><p><a href="/wiki/Search_engine" title="Search engine">Search engines</a> also often make <a href="/wiki/Web_page" class="mw-redirect" title="Web page">web pages</a> they have indexed available from their cache. For example, <a href="/wiki/Google" title="Google">Google</a> provides a "Cached" link next to each search result. This is useful when web pages are temporarily inaccessible from a <a href="/wiki/Server" title="Server">web server</a>. </p> <div class="mw-heading mw-heading3"><h3 id="Caching_with_unreliable_networks">Caching with unreliable networks</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Cache_(computing)&veaction=edit&section=10" title="Change section: Caching with unreliable networks" class="mw-editsection-visualeditor"><span>change</span></a><span class="mw-editsection-divider"> | </span><a href="/w/index.php?title=Cache_(computing)&action=edit&section=10" title="Edit section's source code: Caching with unreliable networks"><span>change source</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Write-through operation is common in unreliable networks (like an <a href="/wiki/Ethernet" title="Ethernet">Ethernet</a> <a href="/wiki/LAN" class="mw-redirect" title="LAN">LAN</a>). The protocol used to make sure the data in the write cache makes sense when several write caches are used is very complex, in such a case. </p><p>For instance, web page caches and <a href="/w/index.php?title=Client-side&action=edit&redlink=1" class="new" title="Client-side (not yet started)">client-side</a> <a href="/wiki/Network_File_System" title="Network File System">network file system</a> caches (like those in <a href="/wiki/Network_File_System_(protocol)" class="mw-redirect" title="Network File System (protocol)">NFS</a> or <a href="/w/index.php?title=Server_Message_Block&action=edit&redlink=1" class="new" title="Server Message Block (not yet started)">SMB</a>) are typically read-only or write-through to keep the network protocol simple and reliable. </p> <div class="mw-heading mw-heading2"><h2 id="The_difference_between_buffer_and_cache">The difference between buffer and cache</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Cache_(computing)&veaction=edit&section=11" title="Change section: The difference between buffer and cache" class="mw-editsection-visualeditor"><span>change</span></a><span class="mw-editsection-divider"> | </span><a href="/w/index.php?title=Cache_(computing)&action=edit&section=11" title="Edit section's source code: The difference between buffer and cache"><span>change source</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Buffer and cache are not mutually exclusive; they are also often used together. The reason why they are used is different, though. A buffer is a location in memory that is traditionally used because CPU <a href="/wiki/Instruction_(computer_science)" title="Instruction (computer science)">instructions</a> cannot directly address data stored in peripheral devices. Computer memory is used as an intermediate store. </p><p>Additionally such a buffer may be feasible when a large block of data is assembled or disassembled (as required by a storage device), or when data may be delivered in a different order than that in which it is produced. Also a whole buffer of data is usually transferred sequentially (for example to hard disk), so buffering itself sometimes increases transfer performance. These benefits are present even if the buffered data are written to the <a href="/w/index.php?title=Buffer&action=edit&redlink=1" class="new" title="Buffer (not yet started)">buffer</a> once and read from the buffer once. </p><p>A cache also increases transfer performance. A part of the increase similarly comes from the possibility that multiple small transfers will combine into one large block. But the main performance gain occurs because there is a good chance that the same datum will be read from cache several times, or that written data will soon be read. The only purpose of Caches is to reduce accesses to the underlying slower storage. Cache is also usually an <a href="/w/index.php?title=Abstraction_layer&action=edit&redlink=1" class="new" title="Abstraction layer (not yet started)">abstraction layer</a> that is designed to be invisible from the perspective of neighboring layers. That way, the applications or clients may not be aware that there is a cache. </p> <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=Cache_(computing)&veaction=edit&section=12" title="Change section: References" class="mw-editsection-visualeditor"><span>change</span></a><span class="mw-editsection-divider"> | </span><a href="/w/index.php?title=Cache_(computing)&action=edit&section=12" title="Edit section's source code: References"><span>change source</span></a><span class="mw-editsection-bracket">]</span></span></div> <style data-mw-deduplicate="TemplateStyles:r9724317">.mw-parser-output .reflist{margin-bottom:0.5em;list-style-type:decimal}@media screen{.mw-parser-output .reflist{font-size:90%}}.mw-parser-output .reflist .references{font-size:100%;margin-bottom:0;list-style-type:inherit}.mw-parser-output .reflist-columns-2{column-width:30em}.mw-parser-output .reflist-columns-3{column-width:25em}.mw-parser-output .reflist-columns{margin-top:0.3em}.mw-parser-output .reflist-columns ol{margin-top:0}.mw-parser-output .reflist-columns li{page-break-inside:avoid;break-inside:avoid-column}.mw-parser-output .reflist-upper-alpha{list-style-type:upper-alpha}.mw-parser-output .reflist-upper-roman{list-style-type:upper-roman}.mw-parser-output .reflist-lower-alpha{list-style-type:lower-alpha}.mw-parser-output .reflist-lower-greek{list-style-type:lower-greek}.mw-parser-output .reflist-lower-roman{list-style-type:lower-roman}</style><div class="reflist"> <div class="mw-references-wrap"><ol class="references"> <li id="cite_note-1"><span class="mw-cite-backlink"><a href="#cite_ref-1">↑</a></span> <span class="reference-text"><style data-mw-deduplicate="TemplateStyles:r9724332">.mw-parser-output cite.citation{font-style:inherit;word-wrap:break-word}.mw-parser-output .citation q{quotes:"\"""\"""'""'"}.mw-parser-output .citation:target{background-color:rgba(0,127,255,0.133)}.mw-parser-output .id-lock-free.id-lock-free a{background:url("//upload.wikimedia.org/wikipedia/commons/6/65/Lock-green.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-limited.id-lock-limited a,.mw-parser-output .id-lock-registration.id-lock-registration a{background:url("//upload.wikimedia.org/wikipedia/commons/d/d6/Lock-gray-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-subscription.id-lock-subscription a{background:url("//upload.wikimedia.org/wikipedia/commons/a/aa/Lock-red-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .cs1-ws-icon a{background:url("//upload.wikimedia.org/wikipedia/commons/4/4c/Wikisource-logo.svg")right 0.1em center/12px no-repeat}body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-free a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-limited a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-registration a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-subscription a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .cs1-ws-icon a{background-size:contain;padding:0 1em 0 0}.mw-parser-output .cs1-code{color:inherit;background:inherit;border:none;padding:inherit}.mw-parser-output .cs1-hidden-error{display:none;color:var(--color-error,#d33)}.mw-parser-output .cs1-visible-error{color:var(--color-error,#d33)}.mw-parser-output .cs1-maint{display:none;color:#085;margin-left:0.3em}.mw-parser-output .cs1-kern-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right{padding-right:0.2em}.mw-parser-output .citation .mw-selflink{font-weight:inherit}@media screen{.mw-parser-output .cs1-format{font-size:95%}html.skin-theme-clientpref-night .mw-parser-output .cs1-maint{color:#18911f}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .cs1-maint{color:#18911f}}</style><cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://www.oxfordlearnersdictionaries.com/definition/english/cache_1">"cache noun"</a>. <i>Oxford Learner's Dictionaries</i>. Oxford University Press.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=Oxford+Learner%27s+Dictionaries&rft.atitle=cache+noun&rft_id=http%3A%2F%2Fwww.oxfordlearnersdictionaries.com%2Fdefinition%2Fenglish%2Fcache_1&rfr_id=info%3Asid%2Fsimple.wikipedia.org%3ACache+%28computing%29" class="Z3988"></span></span> </li> <li id="cite_note-2"><span class="mw-cite-backlink"><a href="#cite_ref-2">↑</a></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r9724332"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://dictionary.cambridge.org/dictionary/british/cache">"cache definition, meaning"</a>. <i>Cambridge Dictionaries Online</i>. Cambridge University Press.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=Cambridge+Dictionaries+Online&rft.atitle=cache+definition%2C+meaning&rft_id=http%3A%2F%2Fdictionary.cambridge.org%2Fdictionary%2Fbritish%2Fcache&rfr_id=info%3Asid%2Fsimple.wikipedia.org%3ACache+%28computing%29" class="Z3988"></span></span> </li> <li id="cite_note-3"><span class="mw-cite-backlink"><a href="#cite_ref-3">↑</a></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r9724332"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://www.merriam-webster.com/dictionary/cache">"Cache"</a>. <i>Merriam-Webster Online Dictionary</i>. Merriam-Webster, Incorporated.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=Merriam-Webster+Online+Dictionary&rft.atitle=Cache&rft_id=http%3A%2F%2Fwww.merriam-webster.com%2Fdictionary%2Fcache&rfr_id=info%3Asid%2Fsimple.wikipedia.org%3ACache+%28computing%29" class="Z3988"></span></span> </li> <li id="cite_note-4"><span class="mw-cite-backlink"><a href="#cite_ref-4">↑</a></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r9724332"><cite id="CITEREFBach,_MartinShaw,_Steve2010" class="citation book cs1">Bach, Martin; Shaw, Steve (September 2010). <a rel="nofollow" class="external text" href="https://books.google.com/books?id=XSjU2Fv4MYwC"><i>Pro Oracle Database 11g RAC on Linux</i></a> (2nd ed.). Apress. p. 257. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/978-1430229582" title="Special:BookSources/978-1430229582"><bdi>978-1430229582</bdi></a><span class="reference-accessdate">. Retrieved <span class="nowrap">10 March</span> 2011</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Pro+Oracle+Database+11g+RAC+on+Linux&rft.pages=257&rft.edition=2nd&rft.pub=Apress&rft.date=2010-09&rft.isbn=978-1430229582&rft.au=Bach%2C+Martin&rft.au=Shaw%2C+Steve&rft_id=https%3A%2F%2Fbooks.google.com%2Fbooks%3Fid%3DXSjU2Fv4MYwC&rfr_id=info%3Asid%2Fsimple.wikipedia.org%3ACache+%28computing%29" class="Z3988"></span></span> </li> <li id="cite_note-5"><span class="mw-cite-backlink"><a href="#cite_ref-5">↑</a></span> <span class="reference-text">G. C. Stierhoff and A. G. Davis. A History of the IBM Systems Journal. <i>IEEE Annals of the History of Computing</i>, Vol. 20, No. 1 (Jan. 1998), pages 29-35. <a rel="nofollow" class="external autonumber" href="https://dx.doi.org/10.1109/85.646206">[1]</a> </span> </li> </ol></div></div>    </div><noscript><img src="https://login.wikimedia.org/wiki/Special:CentralAutoLogin/start?type=1x1&useformat=desktop" alt="" width="1" height="1" style="border: none; position: absolute;"></noscript> <div class="printfooter" data-nosnippet="">Retrieved from "<a dir="ltr" href="https://simple.wikipedia.org/w/index.php?title=Cache_(computing)&oldid=9858951">https://simple.wikipedia.org/w/index.php?title=Cache_(computing)&oldid=9858951</a>"</div></div> <div id="catlinks" class="catlinks" data-mw="interface"><div id="mw-normal-catlinks" class="mw-normal-catlinks"><a href="/wiki/Special:Categories" title="Special:Categories">Category</a>: <ul><li><a href="/wiki/Category:Computer_science" title="Category:Computer science">Computer science</a></li></ul></div><div id="mw-hidden-catlinks" class="mw-hidden-catlinks mw-hidden-cats-hidden">Hidden category: <ul><li><a href="/wiki/Category:Pages_using_the_JsonConfig_extension" title="Category:Pages using the JsonConfig extension">Pages using the JsonConfig extension</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 changed on 1 November 2024, at 18:21.</li> <li id="footer-info-copyright">Text is available under the <a rel="nofollow" class="external text" href="//creativecommons.org/licenses/by-sa/4.0/">Creative Commons Attribution-ShareAlike License</a> and the <a href="/wiki/Wikipedia:Text_of_the_GNU_Free_Documentation_License" title="Wikipedia:Text of the GNU Free Documentation License">GFDL</a>; additional terms may apply. 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