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<span id="openzim-page-title" class="mw-page-title-main"><span class="mw-page-title-main">System generation</span></span>
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<p>In <a href="Computing" title="Computing">computing</a> <b>system generation</b> or <b>sysgen</b> is the process of creating a particular unique instance of an <a href="Operating_system" title="Operating system">operating system</a> by combining user-specified options and parameters with manufacturer-supplied general-purpose program code to produce an operating system tailored for a particular hardware and software environment.<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> The term is primarily used when referencing older <a href="Mainframe" class="mw-redirect" title="Mainframe">mainframe</a> and <a href="Minicomputer" title="Minicomputer">minicomputer</a> operating systems.
</p><p>Some other programs have similar processes, although not usually called "sysgen." For example, <a href="IBM" title="IBM">IBM</a>'s <a href="Customer_Information_Control_System" class="mw-redirect" title="Customer Information Control System">Customer Information Control System</a> (CICS) was installed through a process called <i>CICSGEN</i>.
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<div class="mw-heading mw-heading2"><h2 id="Rationale">Rationale</h2></div>
<p>A large general-purpose program such as an operating system has to provide support for all variations of <a href="Central_processing_unit" title="Central processing unit">Central processing unit</a> (CPU) that it might be run on, for all supported <a href="Main_memory" class="mw-redirect" title="Main memory">main memory</a> sizes, and for all possible configurations of <a href="Input/output" title="Input/output">input/output</a> (I/O) equipment. No one installation requires all this support, so system generation provides a process for selecting the options and features actually required on any one system.
</p><p>Sysgen produces a system that is most efficient in terms of CPU time, main memory requirements, I/O activity, and/or disk space. Often these parameters can be traded off, for example to generate a system that requires less memory at the expense of increased disk I/O operations.
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<div class="mw-heading mw-heading2"><h2 id="Examples">Examples</h2></div>
<ul><li>The <a href="Burroughs_large_systems" class="mw-redirect" title="Burroughs large systems">Burroughs large systems</a> <a href="Burroughs_MCP" title="Burroughs MCP">Master Control Programs</a> (MCP) were written in high-level <a href="ALGOL" title="ALGOL">ALGOL</a>-like languages <a href="Executive_Systems_Problem_Oriented_Language" class="mw-redirect" title="Executive Systems Problem Oriented Language">ESPOL</a> or <a href="NEWP" class="mw-redirect" title="NEWP">NEWP</a>. The MCP is tailored by coding $OMIT conditional-compilation <a href="Directive_(programming)" title="Directive (programming)">pragmas</a>, which conditionally bypass compilation of specified pieces of code.<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></li>
<li>IBM <a href="System/360" class="mw-redirect" title="System/360">System/360</a> <a href="DOS/360_and_successors" title="DOS/360 and successors">Disk Operating System (DOS)</a> was written in assembler. The systems programmer performing the sysgen codes assembler <a href="Macro_(computer_science)" title="Macro (computer science)">macros</a> specifying the desired options and assembles the supervisor.</li>
<li><a href="IBM" title="IBM">IBM</a> <a href="OS/360_and_successors" title="OS/360 and successors">OS/360</a> <a href="System_Generation_(OS)" title="System Generation (OS)">had a two-step procedure</a> called <i>Stage I</i> and <i>Stage II</i>. In Stage I the programmer specified the options for the system in a set of macros and assembled them. The output of Stage I was a <a href="Job_stream" title="Job stream">job stream</a> which contained the <a href="Job_Control_Language" title="Job Control Language">job control</a> to perform all the necessary assemblies, link edits, and to create the required system libraries and copy the necessary modules into them.<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></li>
<li><a href="RSX-11" title="RSX-11">RSX-11M</a> had a three-phase SYSGEN that was required to add new hardware to the base executive.<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></li></ul>
<div class="mw-heading mw-heading2"><h2 id="See_also">See also</h2></div>
<ul><li><a href="System_Generation_(OS)" title="System Generation (OS)">System Generation (OS)</a></li></ul>
<div class="mw-heading mw-heading2"><h2 id="References">References</h2></div>
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<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">
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</style><cite id="CITEREFFarlex" class="citation web cs1">Farlex. <a rel="nofollow" class="external text" href="http://encyclopedia2.thefreedictionary.com/system+generation">"The Free Dictionary"</a><span class="reference-accessdate">. Retrieved <span class="nowrap">June 21,</span> 2013</span>.</cite></span>
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<li id="cite_note-2"><span class="mw-cite-backlink"><b><a href="#cite_ref-2">^</a></b></span> <span class="reference-text"><cite id="CITEREFKimpel" class="citation web cs1">Kimpel, Paul. <a rel="nofollow" class="external text" href="http://retro-b5500.blogspot.com/">"End of the Summer Update"</a>. <i>B5500 Emulation Project</i><span class="reference-accessdate">. Retrieved <span class="nowrap">June 21,</span> 2013</span>.</cite></span>
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<li id="cite_note-3"><span class="mw-cite-backlink"><b><a href="#cite_ref-3">^</a></b></span> <span class="reference-text"><cite id="CITEREFIBM_Corporation1966" class="citation book cs1">IBM Corporation (1966). <a rel="nofollow" class="external text" href="http://bitsavers.trailing-edge.com/pdf/ibm/360/os/R01-08/C28-6554-1_System_Generation_Oct66.pdf"><i>IBM System/360 Operating System System Generation</i></a> <span class="cs1-format">(PDF)</span>.</cite></span>
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<li id="cite_note-4"><span class="mw-cite-backlink"><b><a href="#cite_ref-4">^</a></b></span> <span class="reference-text"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://ancientbits.blogspot.com/2012/07/installing-rsx-11m-46-from-scratch-part_12.html">"Installing RSX-11M 4.6 from scratch - Part 2: System generation (SYSGEN)"</a>. <i>The Ancient Bits adventure</i>. July 12, 2012<span class="reference-accessdate">. Retrieved <span class="nowrap">May 21,</span> 2025</span>.</cite></span>
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