{"id":118,"date":"2023-06-11T19:47:41","date_gmt":"2023-06-11T19:47:41","guid":{"rendered":"https:\/\/learnlearn.uk\/edexcel-igcse-computer-science\/?page_id=118"},"modified":"2023-06-11T19:47:41","modified_gmt":"2023-06-11T19:47:41","slug":"fetch-execute-cycle","status":"publish","type":"page","link":"https:\/\/learnlearn.uk\/edexcel-igcse-computer-science\/fetch-execute-cycle\/","title":{"rendered":"Fetch &#8211; Execute Cycle"},"content":{"rendered":"<div class=\"responsive-tabs\">\n<h2 class=\"tabtitle\">Introduction<\/h2>\n<div class=\"tabcontent\">\n\n<h2>Fetch Decode Execute Cycle<\/h2>\n<p><a href=\"https:\/\/www.hartismere.com\/20398\/CPU-Fetch-Decode-Execute-Animation\">Excellent animation available here<\/a><\/p>\n<p>The fetch decode execute cycle is the process the computer goes through when processing instructions. The cycle is performed constantly from boot up, until the computer is shutdown.<\/p>\n<p><img decoding=\"async\" loading=\"lazy\" class=\"alignnone wp-image-453 size-full\" src=\"https:\/\/learnlearn.uk\/gcsecs\/wp-content\/uploads\/sites\/8\/2018\/01\/fetch-decode-execute-oct-gcse.png\" alt=\"fetch decode execute cycle ocr\" width=\"592\" height=\"397\" \/><\/p>\n\n<\/div><h2 class=\"tabtitle\">Tutorial Video<\/h2>\n<div class=\"tabcontent\">\n\n<div class=\"nv-iframe-embed\">\n<div class=\"container-lazyload preview-lazyload container-youtube js-lazyload--not-loaded\"><a href=\"https:\/\/www.youtube.com\/watch?v=IL44-Mfp8x4\" class=\"lazy-load-youtube preview-lazyload preview-youtube\" data-video-title=\"Fetch decode execute cycle\" title=\"Play video &quot;Fetch decode execute cycle&quot;\">https:\/\/www.youtube.com\/watch?v=IL44-Mfp8x4<\/a><noscript>Video can&#8217;t be loaded because JavaScript is disabled: <a href=\"https:\/\/www.youtube.com\/watch?v=IL44-Mfp8x4\" title=\"Fetch decode execute cycle\">Fetch decode execute cycle (https:\/\/www.youtube.com\/watch?v=IL44-Mfp8x4)<\/a><\/noscript><\/div>\n<\/div>\n<p>&nbsp;<\/p>\n<p><a href=\"https:\/\/www.futurelearn.com\/info\/courses\/how-computers-work\/0\/steps\/49284\">Fetch Execute Cycle video with opcodes &amp; operands<\/a><\/p>\n\n<\/div><h2 class=\"tabtitle\">Fetch<\/h2>\n<div class=\"tabcontent\">\n\n<h3>Fetch Phase<\/h3>\n<p>In this phase of the cycle, the processor:<\/p>\n<ol>\n<li>Gets the memory address of the current instruction from the program counter PC<\/li>\n<li>Passes the address to the memory address register<\/li>\n<li>Sends the address along the address bus.<\/li>\n<li>The RAM retrieves the data stored at that address and passes the data back along the data bus.<\/li>\n<li>The data is the stored in the memory data register (MDR) ready for decoding.<\/li>\n<\/ol>\n\n<\/div><h2 class=\"tabtitle\">Decode<\/h2>\n<div class=\"tabcontent\">\n\n<h3>Decode Phase<\/h3>\n<p>In this phase the data in the MDR is passed to the control unit (CU) which then decodes the instruction and then signals to the ALU what instruction is to be completed.<\/p>\n\n<\/div><h2 class=\"tabtitle\">Execute<\/h2>\n<div class=\"tabcontent\">\n\n<h3>Execute Phase<\/h3>\n<p>In the final phase of the fetch decode execute cycle the instruction is executed.<\/p>\n<p>This instruction could comprise of:<\/p>\n<ul>\n<li>Reading operand data in to the accumulator from the RAM<\/li>\n<li>Performing arithmetic\u00a0 on operand data<\/li>\n<li>Performing logical functions (conditionals \/ loops)<\/li>\n<li>Writing data from the accumulator to the RAM<\/li>\n<\/ul>\n<p>Once this step is complete the CPU moves on to the next instruction<\/p>\n\n<\/div><h2 class=\"tabtitle\">Operands vs Opcodes<\/h2>\n<div class=\"tabcontent\">\n\n<p><strong>Operands vs Opcodes<\/strong><\/p>\n<p>An opcode is a single instruction that tells the process what operation to perform. An operand is the data or location on which the operation will be performed.<\/p>\n<p><strong>ADD 4<\/strong><\/p>\n<p>Opcode = ADD\u00a0 Operand = 4\u00a0 \u00a0&#8211; This means add the number stored at memory location 4 to the number stored in the accumulator.<\/p>\n<p>Full Example<\/p>\n<ul>\n<li>LOAD 3<\/li>\n<li>SUB 4<\/li>\n<li>STORE 5<\/li>\n<\/ul>\n<p>This example means:<\/p>\n<ol>\n<li>load the contents of memory location 3 in to the accumulator<\/li>\n<li>Subtract the contents of memory location 4 from the data in the accumulator<\/li>\n<li>Store the result of the subtraction to memory location 5<\/li>\n<\/ol>\n\n<\/div><h2 class=\"tabtitle\">Resources<\/h2>\n<div class=\"tabcontent\">\n\n<h3>Resources<\/h3>\n<p><a href=\"https:\/\/www.aicurriculum.co.uk\/resources\/ffdacbfb-1e28-49e5-a978-a168396aaa04\">Free online &amp; printable study &amp; teaching resources<\/a><\/p>\n<p><a href=\"https:\/\/docs.google.com\/drawings\/d\/1I3EdK4tsuVpLfwCZ6RX4NHAjlxx2dvbCBpvdJzS2nTo\/edit?usp=sharing\">Blank Worksheet<\/a><\/p>\n<p><a href=\"https:\/\/play.kahoot.it\/#\/k\/911d715c-e3b4-4ff2-9eea-4b88b9484357\">Topic Review Kahoot<\/a><\/p>\n<p>&nbsp;<\/p>\n<p><strong>Past Paper Questions<\/strong><\/p>\n<p><a href=\"http:\/\/www.coverpapers.com\/index.php?lv=15&amp;sj=40&amp;bd=11\">S 15\u00a0 Paper 12 Question 8 C<\/a><\/p>\n<p><a href=\"http:\/\/www.coverpapers.com\/index.php?lv=15&amp;sj=40&amp;bd=11\">N15 Paper 12 Question 8<\/a><\/p>\n<p><a href=\"http:\/\/www.coverpapers.com\/index.php?lv=15&amp;sj=40&amp;bd=11\">S16 Paper 12 Question 3<\/a><\/p>\n<p>N16 Paper 12 Question 8<\/p>\n<p><a href=\"https:\/\/pastpapers.papacambridge.com\/view.php?id=Cambridge%20International%20Examinations%20%28CIE%29\/AS%20and%20A%20Level\/Computer%20Science%20-%209608\/2019-May-June\/9608_s19_qp_12.pdf\">J19 Paper 12 Question 3<\/a><\/p>\n<\/div><\/div>\n","protected":false},"excerpt":{"rendered":"<p>Fetch Decode Execute Cycle Excellent animation available here The fetch decode execute cycle is the process the computer goes through when processing instructions. The cycle is performed constantly from boot up, until the computer is shutdown. https:\/\/www.youtube.com\/watch?v=IL44-Mfp8x4Video can&#8217;t be loaded because JavaScript is disabled: Fetch decode execute cycle (https:\/\/www.youtube.com\/watch?v=IL44-Mfp8x4) &nbsp; Fetch Execute Cycle video with&hellip;&nbsp;<a href=\"https:\/\/learnlearn.uk\/edexcel-igcse-computer-science\/fetch-execute-cycle\/\" class=\"\" rel=\"bookmark\">Read More &raquo;<span class=\"screen-reader-text\">Fetch &#8211; Execute Cycle<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"neve_meta_sidebar":"","neve_meta_container":"","neve_meta_enable_content_width":"off","neve_meta_content_width":100,"neve_meta_title_alignment":"","neve_meta_author_avatar":"","neve_post_elements_order":"","neve_meta_disable_header":"","neve_meta_disable_footer":"","neve_meta_disable_title":""},"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v20.6 - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>Fetch &#8211; Execute Cycle - Edexcel iGCSE Computer Science<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/learnlearn.uk\/edexcel-igcse-computer-science\/fetch-execute-cycle\/\" \/>\n<meta property=\"og:locale\" content=\"en_GB\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Fetch &#8211; Execute Cycle - Edexcel iGCSE Computer Science\" \/>\n<meta property=\"og:description\" content=\"Fetch Decode Execute Cycle Excellent animation available here The fetch decode execute cycle is the process the computer goes through when processing instructions. The cycle is performed constantly from boot up, until the computer is shutdown. https:\/\/www.youtube.com\/watch?v=IL44-Mfp8x4Video can&#8217;t be loaded because JavaScript is disabled: Fetch decode execute cycle (https:\/\/www.youtube.com\/watch?v=IL44-Mfp8x4) &nbsp; Fetch Execute Cycle video with&hellip;&nbsp;Read More &raquo;Fetch &#8211; Execute Cycle\" \/>\n<meta property=\"og:url\" content=\"https:\/\/learnlearn.uk\/edexcel-igcse-computer-science\/fetch-execute-cycle\/\" \/>\n<meta property=\"og:site_name\" content=\"Edexcel iGCSE Computer Science\" \/>\n<meta property=\"og:image\" content=\"http:\/\/learnlearn.uk\/gcsecs\/wp-content\/uploads\/sites\/8\/2018\/01\/fetch-decode-execute-oct-gcse.png\" \/>\n<meta name=\"twitter:card\" content=\"summary_large_image\" \/>\n<meta name=\"twitter:label1\" content=\"Estimated reading time\" \/>\n\t<meta name=\"twitter:data1\" content=\"2 minutes\" \/>\n<script type=\"application\/ld+json\" class=\"yoast-schema-graph\">{\"@context\":\"https:\/\/schema.org\",\"@graph\":[{\"@type\":\"WebPage\",\"@id\":\"https:\/\/learnlearn.uk\/edexcel-igcse-computer-science\/fetch-execute-cycle\/\",\"url\":\"https:\/\/learnlearn.uk\/edexcel-igcse-computer-science\/fetch-execute-cycle\/\",\"name\":\"Fetch &#8211; Execute Cycle - Edexcel iGCSE Computer Science\",\"isPartOf\":{\"@id\":\"https:\/\/learnlearn.uk\/edexcel-igcse-computer-science\/#website\"},\"datePublished\":\"2023-06-11T19:47:41+00:00\",\"dateModified\":\"2023-06-11T19:47:41+00:00\",\"breadcrumb\":{\"@id\":\"https:\/\/learnlearn.uk\/edexcel-igcse-computer-science\/fetch-execute-cycle\/#breadcrumb\"},\"inLanguage\":\"en-GB\",\"potentialAction\":[{\"@type\":\"ReadAction\",\"target\":[\"https:\/\/learnlearn.uk\/edexcel-igcse-computer-science\/fetch-execute-cycle\/\"]}]},{\"@type\":\"BreadcrumbList\",\"@id\":\"https:\/\/learnlearn.uk\/edexcel-igcse-computer-science\/fetch-execute-cycle\/#breadcrumb\",\"itemListElement\":[{\"@type\":\"ListItem\",\"position\":1,\"name\":\"Home\",\"item\":\"https:\/\/learnlearn.uk\/edexcel-igcse-computer-science\/\"},{\"@type\":\"ListItem\",\"position\":2,\"name\":\"Fetch &#8211; Execute Cycle\"}]},{\"@type\":\"WebSite\",\"@id\":\"https:\/\/learnlearn.uk\/edexcel-igcse-computer-science\/#website\",\"url\":\"https:\/\/learnlearn.uk\/edexcel-igcse-computer-science\/\",\"name\":\"Edexcel iGCSE Computer Science\",\"description\":\"\",\"potentialAction\":[{\"@type\":\"SearchAction\",\"target\":{\"@type\":\"EntryPoint\",\"urlTemplate\":\"https:\/\/learnlearn.uk\/edexcel-igcse-computer-science\/?s={search_term_string}\"},\"query-input\":\"required name=search_term_string\"}],\"inLanguage\":\"en-GB\"}]}<\/script>\n<!-- \/ Yoast SEO plugin. -->","yoast_head_json":{"title":"Fetch &#8211; Execute Cycle - Edexcel iGCSE Computer Science","robots":{"index":"index","follow":"follow","max-snippet":"max-snippet:-1","max-image-preview":"max-image-preview:large","max-video-preview":"max-video-preview:-1"},"canonical":"https:\/\/learnlearn.uk\/edexcel-igcse-computer-science\/fetch-execute-cycle\/","og_locale":"en_GB","og_type":"article","og_title":"Fetch &#8211; Execute Cycle - Edexcel iGCSE Computer Science","og_description":"Fetch Decode Execute Cycle Excellent animation available here The fetch decode execute cycle is the process the computer goes through when processing instructions. 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The cycle is performed constantly from boot up, until the computer is shutdown. https:\/\/www.youtube.com\/watch?v=IL44-Mfp8x4Video can&#8217;t be loaded because JavaScript is disabled: Fetch decode execute cycle (https:\/\/www.youtube.com\/watch?v=IL44-Mfp8x4) &nbsp; Fetch Execute Cycle video with&hellip;&nbsp;Read&hellip;","_links":{"self":[{"href":"https:\/\/learnlearn.uk\/edexcel-igcse-computer-science\/wp-json\/wp\/v2\/pages\/118"}],"collection":[{"href":"https:\/\/learnlearn.uk\/edexcel-igcse-computer-science\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/learnlearn.uk\/edexcel-igcse-computer-science\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/learnlearn.uk\/edexcel-igcse-computer-science\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/learnlearn.uk\/edexcel-igcse-computer-science\/wp-json\/wp\/v2\/comments?post=118"}],"version-history":[{"count":1,"href":"https:\/\/learnlearn.uk\/edexcel-igcse-computer-science\/wp-json\/wp\/v2\/pages\/118\/revisions"}],"predecessor-version":[{"id":119,"href":"https:\/\/learnlearn.uk\/edexcel-igcse-computer-science\/wp-json\/wp\/v2\/pages\/118\/revisions\/119"}],"wp:attachment":[{"href":"https:\/\/learnlearn.uk\/edexcel-igcse-computer-science\/wp-json\/wp\/v2\/media?parent=118"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}