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<!--replace-end-7--><!--replace-end-4--><!--replace-end-1--></head><body><div class="ui fluid container universe"><!--replace-start-2--><!--replace-start-3--><!--replace-start-6--><div class="ui text container" id="zettel-container" style="position: relative"><div class="zettel-view"><article class="ui raised attached segment zettel-content"><div class="pandoc"><h1 id="title-h1">Operating system API</h1><p>A user can interact with the operating system either via the GUI or the <span class="zettel-link-container cf"><span class="zettel-link" title="Zettel: Introduction to the Unix shell"><a href="Intro_to_the_Unix_shell.html">shell</a></span></span>. (Both ultimately access the OS via the shell since the UI is an abstraction layer of the shell.)</p><p>When <em>programs</em> interact with the operating system they use the <strong>operating system’s API</strong> directly. The GUI and shell also invoke the OS API but the access is mediated.</p><p>Every OS has an API. This specification details how a program should interact with the OS, exposing functions, properties and data types.</p><p>Whether using the GUI or a terminal emulator, the shell translates the user’s commands into API calls. The API the invokes internal operating system code to perform the action.</p><p><img alt="OS API diagram" src="/static/OS-api.svg" /></p><h2 id="example-opening-a-file">Example: opening a file</h2><p>A user can use a file explorer and the mouse to open a file. Or they can open the file by invoking it from the terminal.</p><p>A running application doesn’t have to do this. If it’s remit includes opening files, it can do so by calling the OS API.</p><p>On a Unix-like system the applicaton would use the <code>open</code> API function to open the file:</p><pre><code class="language-none">open("foo.txt", 0_WRONLY|0_CREAT)</code></pre><p>This command makes the action write-only and creates the file because it does not yet exist. When the user opens a file in their File Explorer, the application translates their graphical actions into this API call.</p><h2 id="different-oss-have-different-apis">Different OSs have different APIs</h2><p>Unix-like and Linux operating systems use variations on the <strong>Portable Operating System Interface</strong> (POSIX) standard. This defines the OS API and also the rules for the shell’s behaviour and its included utilities.</p><p>Variations on this include <em>Cocoa</em>, macOS’s API and Android’s <em>Android Platform</em> API.</p><p>Windows has its own API called <em>The Windows API</em>. The original version was 16-bit called <em>Win16</em>, then when it moved to 32-bits it became <em>Win32</em>. When it moved to an x86 <span class="zettel-link-container cf"><span class="zettel-link" title="Zettel: Instruction Set Architectures"><a href="Instruction_set_architectures.html">instruction_set_architecture</a></span></span> it became <em>Win64</em>. Starting with Windows 10, it introduced the <em>Universal Windows Platform</em> which aims to make app development consistent accross different devices that run Windows.</p></div></article><nav class="ui attached segment deemphasized bottomPane" id="neuron-tags-pane"><div><span class="ui basic label zettel-tag" title="Tag">operating-systems</span></div></nav><nav class="ui bottom attached icon compact inverted menu blue" id="neuron-nav-bar"><!--replace-start-9--><!--replace-end-9--><a class="right item" href="impulse.html" title="Open Impulse"><i class="wave square icon"></i></a></nav></div></div><!--replace-end-6--><!--replace-end-3--><!--replace-end-2--><div class="ui center aligned container footer-version"><div class="ui tiny image"><a href="https://neuron.zettel.page"><img alt="logo" src="https://raw.githubusercontent.com/srid/neuron/master/assets/neuron.svg" title="Generated by Neuron 1.9.35.3" /></a></div></div></div></body></html> |