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<!DOCTYPE html> <html lang="en"> <head> <title>machine code from FOLDOC</title> <meta http-equiv="Content-Security-Policy" content="default-src 'unsafe-inline' http: https:"> <meta name="verify-v1" content="siAI0ZOMn41hao0E/T76D1I2L3MtFjzE48P3ctCjRNU="> <meta charset="utf-8"> <meta name="viewport" content="width=device-width, initial-scale=1"> <meta name="msapplication-TileColor" content="#da532c"> <meta name="theme-color" content="#ffffff"> <meta name="google-translate-customization" content="828219db36930e1e-c51d915bf2ea717c-g9b503f9a85d5b5a7-a">  <script src="https://www.googletagmanager.com/gtag/js?id=UA-9715943-1"></script> <script> window.dataLayer = window.dataLayer || []; function gtag(){dataLayer.push(arguments);} gtag('js', new Date()); gtag('config', 'UA-9715943-1'); </script>  <link href="//fonts.googleapis.com/css?family=Duru+Sans%7CBelgrano%7CInconsolata%7CAlef%7CArmata" rel="stylesheet" type="text/css"> <link rel="stylesheet" type="text/css" href="/css/layout.css?2">  <link rel="apple-touch-icon" sizes="152x152" href="/im/apple-touch-icon.png"> <link rel="icon" type="image/png" sizes="32x32" href="/im/favicon-32x32.png"> <link rel="icon" type="image/png" sizes="16x16" href="/im/favicon-16x16.png"> <link rel="manifest" href="/im/site.webmanifest"> <link rel="mask-icon" href="/im/safari-pinned-tab.svg" color="#5bbad5"> <link rel="canonical" href="https://foldoc.org/machine+code"> <link rel="alternate" type="application/rss+xml" title="FOLDOC" href="/rss.xml"> <link rel="search" title="FOLDOC" type="application/opensearchdescription+xml" href="//foldoc.org/search.xml">  <script async src="https://pagead2.googlesyndication.com/pagead/js/adsbygoogle.js?client=ca-pub-5521724329338202" crossorigin="anonymous"></script>  </head> <body> <div id="fb-root"></div> <script> (function (d, s, id) { var js, fjs = d.getElementsByTagName(s)[0]; if (d.getElementById(id)) return; js = d.createElement(s); js.id = id; js.src = "//connect.facebook.net/en_GB/all.js#xfbml=1"; fjs.parentNode.insertBefore(js, fjs); }(document, 'script', 'facebook-jssdk')); </script> <div id="container"> <div id="left"> <a href="/"> <img src="/foldoc.gif" width="300" height="98" alt="Free On-line Dictionary of Computing" class="logo"> </a> <div id="nav"> <a href="/contents.html" class="button">Contents</a> <a href="/help.html" class="button">Help</a> <a href="/random-entry" class="button">Random</a> </div> <form action="/"> <input type="text" name="query" id="query" autofocus="autofocus"> <input type="submit" name="action" value="Search" class="button"> </form> <div id="content"> <h2>machine code</h2> <p></p> <p><<i><a href="contents/language.html">language</a></i>></p> <p> The representation of a <a href="/computer+program">computer program</a> that is read and interpreted by the computer hardware (rather than by some other machine code program). A program in machine code consists of a sequence of "instructions" (possibly interspersed with data). An instruction is a <a href="/binary+string">binary string</a>, (often written as one or more <a href="/octal">octal</a>, <a href="/decimal">decimal</a> or <a href="/hexadecimal">hexadecimal</a> numbers). Instructions may be all the same size (e.g. one 32-bit word for many modern <a href="/RISC">RISC</a> <a href="/microprocessors">microprocessors</a>) or of different sizes, in which case the size of the instruction is determined from the first <a href="/word">word</a> (e.g. <a href="/Motorola">Motorola</a> <a href="/68000">68000</a>) or <a href="/byte">byte</a> (e.g. <a href="/Inmos">Inmos</a> <a href="/transputer">transputer</a>). The collection of all possible instructions for a particular computer is known as its "<a href="/instruction+set">instruction set</a>". <p></p> Each instruction typically causes the <a href="/Central+Processing+Unit">Central Processing Unit</a> to perform some fairly simple operation like loading a value from memory into a <a href="/register">register</a> or adding the numbers in two registers. An instruction consists of an <a href="/op+code">op code</a> and zero or more <a href="/operands">operands</a>. Different processors have different <a href="/instruction+sets">instruction sets</a> - the collection of possible operations they can perform. <p></p> Execution of machine code may either be <a href="/hard-wired">hard-wired</a> into the <a href="/central+processing+unit">central processing unit</a> or it may be controlled by <a href="/microcode">microcode</a>. The basic execution cycle consists of fetching the next instruction from <a href="/main+memory">main memory</a>, decoding it (determining which action the <a href="/operation+code">operation code</a> specifies and the location of any <a href="/arguments">arguments</a>) and executing it by opening various <a href="/gates">gates</a> (e.g. to allow data to flow from main memory into a CPU <a href="/register">register</a>) and enabling <a href="/functional+units">functional units</a> (e.g. signalling to the <a href="/ALU">ALU</a> to perform an addition). <p></p> Humans almost never write programs directly in machine code. Instead, they use <a href="/programming+languages">programming languages</a>. The simplest kind of programming language is <a href="/assembly+language">assembly language</a> which usually has a one-to-one correspondence with the resulting machine code instructions but allows the use of <a href="/mnemonics">mnemonics</a> (ASCII strings) for the "<a href="/op+codes">op codes</a>" (the part of the instruction which encodes the basic type of operation to perform) and names for locations in the program (branch labels) and for <a href="/variables">variables</a> and <a href="/constants">constants</a>. Other languages are either translated by a <a href="/compiler">compiler</a> into machine code or executed by an <a href="/interpreter">interpreter</a> <p></p> <p class="updated">Last updated: <a href="/new.html">2009-06-16</a></p> <p></p> <p class="vertical-space"></p><h3>Nearby terms:</h3> <p class="neighbours"> <a href="/machine">machine</a> &diams; <b><a href="/machine+code">machine code</a></b> &diams; <a href="/machine+cycle">machine cycle</a> &diams; <a href="/MAchine+INdependent+SAIL">MAchine INdependent SAIL</a> </p> <p> Try this search on <a href="https://www.wikipedia.org/wiki/Special:Search?search=machine+code">Wikipedia</a>, <a href="https://www.wiktionary.org/wiki/machine+code">Wiktionary</a>, <a href="https://www.google.com/search?q=define:machine+code">Google</a>, <a href="https://www.onelook.com/?w=machine+code">OneLook</a>. </p> <p class="vertical-space"></p> <hr> <div></div> <hr>  <div id="HCB_comment_box">Loading</div> <link rel="stylesheet" type="text/css" href="//www.htmlcommentbox.com/static/skins/bootstrap/twitter-bootstrap.css?v=0"> <script language="javascript" id="hcb"> hcb_user = { PAGE: 'https://foldoc.org/machine+code', comments_header: ' ', no_comments_msg: ' ', err_comment_empty: 'Your comment was not posted because it was empty!', rss: '', }; var s = document.createElement("script"); s.setAttribute("type", "text/javascript"); s.setAttribute("src", "//www.htmlcommentbox.com/jread?page=" + escape(hcb_user.PAGE).replace(/\+/g, "%2B") + "&mod=%241%24wq1rdBcg%24.0y2uzvjA2bsnhzpXVq9F." + "&opts=17374&num=10"); // No e-mail field: 16846 if (typeof s != "undefined") document.getElementsByTagName("head")[0].appendChild(s); </script> <script> setTimeout(function () { document.getElementById('hcb_form_content').rows = 1 }, 1000); </script> <hr>  </div>  </div>  <div id="right"> <div id="google_translate_element"> <script> function googleTranslateElementInit() { new google.translate.TranslateElement({ pageLanguage: 'en' }, 'google_translate_element'); } </script> <script src="https://translate.google.com/translate_a/element.js?cb=googleTranslateElementInit"></script> </div> <p><br></p> <hr> <div id="social"> <div class="fb-like" data-href="http://foldoc.org/" data-layout="button_count" data-action="like" data-show-faces="false" data-share="true"> </div> <a href="https://twitter.com/share" class="twitter-share-button" data-via="foldoc"> Tweet </a> <script> if (!document.getElementById('twitter-wjs')) { var fjs = document.getElementsByTagName('script')[0], js = document.createElement('script'); js.id = 'twitter-wjs'; js.src = 'https://platform.twitter.com/widgets.js'; fjs.parentNode.insertBefore(js, fjs); } </script> </div> <hr> <div> <p></p> </div> <p> <a href="/rss.xml"> <img src="/orangerss.gif" width="14" height="14" alt="RSS feed of new items"> </a>   <a href="/new.html">Recent Updates</a>     |     <a href="/missing.html">Missing Terms</a> </p> <p>Updated: Tue, 11 Feb 2025 23:28:55 GMT</p> <p>15282 entries</p> <p><em><a href="/Free+On-line+Dictionary">Copyright Denis Howe 1985</a></em></p> </div>  </div>   <script type="text/javascript"> window._qevents = window._qevents || []; (function() { var elem = document.createElement('script'); elem.src = 'https://secure.quantserve.com/quant.js'; elem.async = true; elem.type = 'text/javascript'; var scpt = document.getElementsByTagName('script')[0]; scpt.parentNode.insertBefore(elem, scpt); })(); window._qevents.push({ qacct: 'p-48Rosdvs3EiOc', uid: '__INSERT_EMAIL_HERE__' }); </script> <noscript> <div style="display:none;"> <img src="https//pixel.quantserve.com/pixel/p-48Rosdvs3EiOc.gif" border="0" height="1" width="1" alt="Quantcast"/> </div> </noscript>  </body> </html>