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<title>RTLinux</title>

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<span id="openzim-page-title" class="mw-page-title-main"><span class="mw-page-title-main">RTLinux</span></span>

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</style><div role="note" class="hatnote navigation-not-searchable">Not to be confused with <a href="Real-Time_Linux" class="mw-redirect" title="Real-Time Linux">Real-Time Linux</a>, the official patchset for real-time support in the Linux kernel.</div>

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</style><table class="infobox vevent"><tbody><tr><th colspan="2" class="infobox-above summary">RTLinux</th></tr><tr><th scope="row" class="infobox-label" style="white-space: nowrap;"><a href="Programmer" title="Programmer">Original author(s)</a></th><td class="infobox-data">Victor Yodaiken, Michael Barabanov</td></tr><tr><th scope="row" class="infobox-label" style="white-space: nowrap;"><a href="Programmer" title="Programmer">Developer(s)</a></th><td class="infobox-data">FSMLabs, <a href="Wind_River_Systems" title="Wind River Systems">Wind River Systems</a></td></tr><tr><th scope="row" class="infobox-label" style="white-space: nowrap;">Written in</th><td class="infobox-data"><a href="C_(programming_language)" title="C (programming language)">C</a></td></tr><tr><th scope="row" class="infobox-label" style="white-space: nowrap;"><a href="Operating_system" title="Operating system">Operating system</a></th><td class="infobox-data"><a href="Linux" title="Linux">Linux</a></td></tr><tr><th scope="row" class="infobox-label" style="white-space: nowrap;">Available in</th><td class="infobox-data"><a href="English_language" title="English language">English</a></td></tr><tr><th scope="row" class="infobox-label" style="white-space: nowrap;"><a href="Software_categories#Categorization_approaches" title="Software categories">Type</a></th><td class="infobox-data"><a href="Kernel_(operating_system)" title="Kernel (operating system)">Kernel</a></td></tr><tr><th scope="row" class="infobox-label" style="white-space: nowrap;"><a href="Software_license" title="Software license">License</a></th><td class="infobox-data"><a href="GNU_General_Public_License#Version_2" title="GNU General Public License">GPL2</a></td></tr></tbody></table>

<p><b>RTLinux</b> is a <a href="Hard_realtime" class="mw-redirect" title="Hard realtime">hard realtime</a> <a href="Real-time_operating_system" title="Real-time operating system">real-time operating system</a> (RTOS) <a href="Microkernel" title="Microkernel">microkernel</a> that runs the entire <a href="Linux" title="Linux">Linux</a> <a href="Operating_system" title="Operating system">operating system</a> as a fully <a href="Preemption_(computing)" title="Preemption (computing)">preemptive</a> process. The hard real-time property makes it possible to control robots, data acquisition systems, manufacturing plants, and other time-sensitive instruments and machines from RTLinux applications. The design was patented.<sup id="cite_ref-RTLinux_Patent_1-0" class="reference"><a href="#cite_note-RTLinux_Patent-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup> Despite the similar name, it is not related to the <a href="Real-Time_Linux" class="mw-redirect" title="Real-Time Linux">Real-Time Linux</a> project of the <a href="Linux_Foundation" title="Linux Foundation">Linux Foundation</a>.<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>

</p><p>RTLinux was developed by Victor Yodaiken, Michael Barabanov, Cort Dougan and others at the <a href="New_Mexico_Institute_of_Mining_and_Technology" title="New Mexico Institute of Mining and Technology">New Mexico Institute of Mining and Technology</a> and then as a commercial product at FSMLabs. <a href="Wind_River_Systems" title="Wind River Systems">Wind River Systems</a> acquired FSMLabs embedded technology in February 2007 and made a version available as Wind River Real-Time Core for <a href="Wind_River_Linux" class="mw-redirect" title="Wind River Linux">Wind River Linux</a>. As of August 2011, Wind River has discontinued the Wind River Real-Time Core product line, effectively ending commercial support for the RTLinux product.

</p>

<div class="mw-heading mw-heading2"><h2 id="Background">Background</h2></div>

<p>The key RTLinux design objective<sup id="cite_ref-Barabanov_3-0" class="reference"><a href="#cite_note-Barabanov-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup> was to add hard real-time capabilities to a commodity operating system to facilitate the development of complex control programs with both capabilities.<sup id="cite_ref-manifesto_4-0" class="reference"><a href="#cite_note-manifesto-4"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-redist_5-0" class="reference"><a href="#cite_note-redist-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup> For example, one might want to develop a real-time motor controller that used a commodity database and exported a web operator interface. Instead of attempting to build a single operating system that could support real-time and non-real-time capabilities, RTLinux was designed to share a computing device between a real-time and non-real-time operating system so that (1) the real-time operating system could never be blocked from execution by the non-real-time operating system and (2) components running in the two different environments could easily share data. As the name implies RTLinux was originally designed to use Linux as the non-real-time system<sup id="cite_ref-barabanov_6-0" class="reference"><a href="#cite_note-barabanov-6"><span class="cite-bracket">[</span>6<span class="cite-bracket">]</span></a></sup> but it eventually evolved so that the RTCore real-time kernel could run with either Linux or <a href="Berkeley_Software_Distribution" title="Berkeley Software Distribution">Berkeley Software Distribution</a> (BSD) <a href="Unix" title="Unix">Unix</a>.

</p><p><a href="Multi-Environment_Real-Time" title="Multi-Environment Real-Time">Multi-Environment Real-Time</a> (MERT) was the first example of a real-time operating system coexisting with a Unix system. MERT relied on traditional virtualization techniques: the real-time kernel was the <i>host</i> operating system (or <a href="Hypervisor" title="Hypervisor">hypervisor</a>) and Bell Systems Unix was the <i>guest</i>. RTLinux was an attempt to update the MERT concept to the PC era and commodity hardware. It was also an attempt to also overcome the performance limits of MERT, particularly the overhead introduced by virtualization.

</p><p>Instead of encapsulating the guest OS in a virtual machine, RTLinux virtualized only the guest interrupt control. This method allowed the real-time kernel to convert the guest operating system into a system that was completely preemptible but that could still directly control, for example, storage devices. In particular, standard drivers for the guest worked without source modification although they needed to be recompiled to use the virtualization "hooks". See also <a href="Paravirtualization" class="mw-redirect" title="Paravirtualization">paravirtualization</a>. The Unix <i><a href="Pipeline_(Unix)" title="Pipeline (Unix)">pipe</a></i> was adapted to permit real-time and non-real-time programs to communicate, although other methods such as shared memory were also added.

</p><p>From the programmer's point of view, RTLinux originally looked like a small threaded environment for real-time tasks plus the standard Linux environment for everything else. The real-time operating system was implemented as a <a href="Loadable_kernel_module" title="Loadable kernel module">loadable kernel module</a> which began by virtualizing guest interrupt control and then started a real-time scheduler. Tasks were assigned static priorities and scheduling was originally purely priority driven. The guest operating system was incorporated as the lowest priority task and essentially acted as the idle task for the real-time system. Real-time tasks ran in kernel mode. Later development of RTLinux adopted the Portable Operating System Interface (<a href="POSIX" title="POSIX">POSIX</a>) <a href="POSIX_threads" class="mw-redirect" title="POSIX threads">POSIX threads</a> application programming interface (<a href="API" title="API">API</a>) and then permitted creation of threads in user mode with real-time threads running inside guest processes. In multiprocessor environments threads were locked to processor cores and it was possible to prevent the guest thread from running on designated core (effectively reserving cores for only real-time processing).

</p>

<div class="mw-heading mw-heading2"><h2 id="Implementation">Implementation</h2></div>

<p>RTLinux provides the ability to run special real-time tasks and interrupt handlers on the same machine as standard Linux. These tasks and handlers execute when they need to execute no matter what Linux is doing. The worst case time between the moment a hardware interrupt is detected by the processor and the moment an interrupt handler starts to execute is under 15 microseconds on RTLinux running on a generic x86 (circa 2000). A RTLinux periodic task runs within 35 microseconds of its scheduled time on the same hardware. These times are hardware limited, and as hardware improves RTLinux will also improve. Standard Linux has excellent average performance and can even provide millisecond level scheduling precision for tasks using the POSIX soft real-time capabilities. Standard Linux is not, however, designed to provide sub-millisecond precision and reliable timing guarantees. RTLinux was based on a lightweight virtual machine where the Linux "guest" was given a virtualized interrupt controller and timer, and all other hardware access was direct. From the point of view of the real-time "host", the Linux kernel is a thread. Interrupts needed for deterministic processing are processed by the real-time core, while other interrupts are forwarded to Linux, which runs at a lower priority than real-time threads. Linux drivers handled almost all <a href="I/O" class="mw-redirect" title="I/O">I/O</a>. First-In-First-Out pipes (<a href="FIFO_(computing_and_electronics)" title="FIFO (computing and electronics)">FIFO</a>) or shared memory can be used to share data between the operating system and RTLinux.

</p>

<div class="mw-heading mw-heading2"><h2 id="Objective">Objective</h2></div>

<p>The key RTLinux design objective is that the system should be transparent, modular, and extensible . Transparency means that there are no unopenable black boxes and the cost of any operation should be determinable. Modularity means that it is possible to omit functionality and the expense of that functionality if it is not needed. And extensibility means that programmers should be able to add modules and tailor the system to their requirements. The base RTLinux system supports high speed interrupt handling and no more. It has simple priority scheduler that can be easily replaced by schedulers more suited to the needs of some specific application. When developing RTLinux, it was designed to maximize the advantage we get from having Linux and its powerful capabilities available.

</p>

<div class="mw-heading mw-heading2"><h2 id="Core_components">Core components</h2></div>

<p>RTLinux is structured as a small core component and a set of optional components. The core component permits installation of very low latency interrupt handlers that cannot be delayed or preempted by Linux itself and some low level synchronization and interrupt control routines. This core component has been extended to support SMP and at the same time it has been simplified by removing some functionality that can be provided outside the core.

</p>

<div class="mw-heading mw-heading2"><h2 id="Functions">Functions</h2></div>

<p>Most RTLinux functions are in a set of loadable kernel modules that provide optional services and levels of abstraction. These modules include:

</p>

<ol><li>rtl sched - a priority scheduler that supports both a "lite POSIX" interface described below and the original V1 RTLinux API.</li>

<li>rtl time - which controls the processor clocks and exports an abstract interface for connecting handlers to clocks.</li>

<li>rtl posixio - supports POSIX style read/write/open interface to device drivers.</li>

<li>rtl fifo - connects RT tasks and interrupt handlers to Linux processes through a device layer so that Linux processes can read/write to RT components.</li>

<li>semaphore - a contributed package by Jerry Epplin which gives RT tasks blocking semaphores.</li>

<li>POSIX mutex support is planned to be available in the next minor version update of RTLinux.</li>

<li>mbuff is a contributed package written by Tomasz Motylewski for providing shared memory between RT components and Linux processes.</li></ol>

<div class="mw-heading mw-heading2"><h2 id="Realtime_tasks">Realtime tasks</h2></div>

<p>RTLinux realtime tasks get implemented as <a href="Kernel_module" class="mw-redirect" title="Kernel module">kernel modules</a> similar to the type of module that Linux uses for drivers, file systems, and so on. Realtime tasks have direct access to the hardware and do not use virtual memory. On initialization, a realtime task (module) informs the RTLinux kernel of its deadline, period, and release-time constraints.

</p>

<div class="mw-heading mw-heading2"><h2 id="Threads">Threads</h2></div>

<p>RT-Linux implements a POSIX API for a thread's manipulation. A thread is created by calling the <code>pthread_create</code> function. The third parameter of <code>pthread_create</code> is a function which contains the code executed by the thread.

</p><p>It is necessary to set thread priorities in RTLinux. Threads with higher priorities can preempt threads with lower priorities. For example, we can have a thread controlling a stepper motor. In order to move the motor fluently, it is necessary to start this thread in strictly regular intervals. This can be guaranteed by assigning a high priority to this thread. The example threads2.c sets different thread priorities. Setting of thread priority is done by code shown below:

</p>

<div class="mw-highlight mw-highlight-lang-c mw-content-ltr" dir="ltr"><pre><span class="kt">int</span><span class="w"> </span><span class="nf">init_module</span><span class="p">(</span><span class="kt">void</span><span class="p">)</span>

<span class="w"> </span><span class="n">pthread_attr_t</span><span class="w"> </span><span class="n">attr</span><span class="p">;</span>

<span class="w"> </span><span class="k">struct</span><span class="w"> </span><span class="nc">sched_param</span><span class="w"> </span><span class="n">param</span><span class="p">;</span>

<span class="w"> </span><span class="n">pthread_attr_init</span><span class="p">(</span><span class="o">&</span><span class="n">attr</span><span class="p">);</span>

<span class="w"> </span><span class="n">param</span><span class="p">.</span><span class="n">sched_priority</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span>

<span class="w"> </span><span class="n">pthread_attr_setschedparam</span><span class="p">(</span><span class="o">&</span><span class="n">attr</span><span class="p">,</span><span class="w"> </span><span class="o">&</span><span class="n">param</span><span class="p">);</span>

<span class="w"> </span><span class="n">pthread_create</span><span class="p">(</span><span class="o">&</span><span class="n">t1</span><span class="p">,</span><span class="w"> </span><span class="o">&</span><span class="n">attr</span><span class="p">,</span><span class="w"> </span><span class="o">&</span><span class="n">thread_code</span><span class="p">,</span><span class="w"> </span><span class="s">"this is thread 1"</span><span class="p">);</span>

<span class="w"> </span><span class="n">rtl_printf</span><span class="p">(</span><span class="s">"Thread 1 started</span><span class="se">\n</span><span class="s">"</span><span class="p">);</span>

</pre></div>

<p>The output the program is as follows.

</p>

<pre>Thread 1 started

Thread 2 started

Thread 3 started

Message: this is thread 1

Message: this is thread 2

Message: this is thread 1

Message: this is thread 3

</pre>

<p>The thread 2 has the highest priority and the thread 3 has the lowest priority. The first message is printed by the middle priority thread 1 because it is started a short time before the thread 2.

</p>

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<ul><li><a href="RTAI" title="RTAI">RTAI</a>. RTAI began as a variant of RTLinux called "MyRTlinux" and in later releases was claimed by its authors not to use the patented RTLinux virtualization technique.</li>

<li><a href="RMX_(operating_system)" title="RMX (operating system)">RMX (operating system)</a></li>

<li><a href="SCHED_DEADLINE" title="SCHED DEADLINE">SCHED_DEADLINE</a></li>

<li><a href="Xenomai" title="Xenomai">Xenomai</a></li>

<li><a href="Preemption_(computing)" title="Preemption (computing)">Preemption (computing)</a></li>

<li><a href="Linux_on_embedded_systems" title="Linux on embedded systems">Linux on embedded systems</a></li>

<li><a href="Real-time_testing" title="Real-time testing">Real-time testing</a></li></ul>

<div class="mw-heading mw-heading2"><h2 id="References">References</h2></div>

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</style><cite id="RTLPATENT" class="citation web cs1">yodaiken, victor. <a rel="nofollow" class="external text" href="https://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&p=1&u=%2Fnetahtml%2FPTO%2Fsearch-bool.html&r=1&f=G&l=50&co1=AND&d=PTXT&s1=5,995,745.PN.&OS=PN/5,995,745&RS=PN/5,995,745">"Adding real-time support to general purpose operating systems"</a>. <i>USPTO</i>. USPTO<span class="reference-accessdate">. Retrieved <span class="nowrap">19 January</span> 2022</span>.</cite></span>

</li>

<li id="cite_note-2"><span class="mw-cite-backlink"><b><a href="#cite_ref-2">^</a></b></span> <span class="reference-text"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://wiki.linuxfoundation.org/realtime/start">"realtime:start [Linux Foundation Wiki]"</a>. <i>wiki.linuxfoundation.org</i>.</cite></span>

</li>

<li id="cite_note-Barabanov-3"><span class="mw-cite-backlink"><b><a href="#cite_ref-Barabanov_3-0">^</a></b></span> <span class="reference-text"><cite id="RTLINUX" class="citation report cs1">Barabanov, Michael. Introducing RTLinux (Report). Linux Journal. <a href="CiteSeerX_(identifier)" class="mw-redirect" title="CiteSeerX (identifier)">CiteSeerX</a> <span class="id-lock-free" title="Freely accessible"><a rel="nofollow" class="external text" href="https://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.302.3221">10.1.1.302.3221</a></span>.</cite></span>

</li>

<li id="cite_note-manifesto-4"><span class="mw-cite-backlink"><b><a href="#cite_ref-manifesto_4-0">^</a></b></span> <span class="reference-text"><cite id="CITEREFYodaiken1999" class="citation report cs1">Yodaiken, Victor (1999). <a rel="nofollow" class="external text" href="http://www.yodaiken.com/papers/rtlmanifesto.pdf">The RTLinux Manifesto</a> <span class="cs1-format">(PDF)</span> (Report). 5th Linux Conference Proceedings.</cite></span>

</li>

<li id="cite_note-redist-5"><span class="mw-cite-backlink"><b><a href="#cite_ref-redist_5-0">^</a></b></span> <span class="reference-text"><cite id="CITEREFYodaiken1996" class="citation report cs1">Yodaiken, Victor (1996). Cheap Operating systems Research (Report). Cambridge, Massachusetts: Proceedings of the First Conference on Freely Redistributable Systems. <a href="CiteSeerX_(identifier)" class="mw-redirect" title="CiteSeerX (identifier)">CiteSeerX</a> <span class="id-lock-free" title="Freely accessible"><a rel="nofollow" class="external text" href="https://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.39.9505">10.1.1.39.9505</a></span>.</cite></span>

</li>

<li id="cite_note-barabanov-6"><span class="mw-cite-backlink"><b><a href="#cite_ref-barabanov_6-0">^</a></b></span> <span class="reference-text"><cite id="CITEREFBarabanov1996" class="citation thesis cs1">Barabanov, Michael (1996). <a rel="nofollow" class="external text" href="http://www.yodaiken.com/papers/BarabanovThesis.pdf"><i>A Linux Based Real-Time Operating System</i></a> <span class="cs1-format">(PDF)</span> (M.S.).</cite></span>

</li>

</ol></div></div>

<div class="mw-heading mw-heading2"><h2 id="Sources">Sources</h2></div>

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<ul><li><a rel="nofollow" class="external text" href="http://www.ddj.com/cpp/184401758">Dougan, Cort (2004), "Precision and predictability for Linux and RTLinuxPro", Dr. Dobbs Journal, February 1, 2004</a></li>

<li><a rel="nofollow" class="external text" href="https://patentimages.storage.googleapis.com/99/da/90/31f19019130256/US5995745.pdf">Yodaiken, Victor (1997), US Patent 5,995,745</a></li></ul>

</div>

<div class="mw-heading mw-heading2"><h2 id="External_links">External links</h2></div>

<ul><li><a rel="nofollow" class="external text" href="http://www.yodaiken.com/papers/sync.pdf">Article about RTLinux synchronization</a></li>

<li><a rel="nofollow" class="external text" href="http://www.soe.ucsc.edu/~sbrandt/courses/Winter00/290S/rtlinux.pdf"><i>A Real-Time Linux</i></a> <a rel="nofollow" class="external text" href="https://web.archive.org/web/20070318062700/http://www.soe.ucsc.edu/~sbrandt/courses/Winter00/290S/rtlinux.pdf">Archived</a> 2007-03-18 at the <a href="Wayback_Machine" title="Wayback Machine">Wayback Machine</a>. Victor Yodaiken and Michael Barabanov, New Mexico Institute of Technology</li>

<li><a rel="nofollow" class="external text" href="https://archive.today/20130128073427/http://www.linuxdevices.com/articles/AT3694406595.html">Article about RT concept</a> at <a href="Archive.today" title="Archive.today">archive.today</a> (archived 2013-01-28)</li></ul>

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<li><a href="Junos_OS" title="Junos OS">Junos OS</a></li>

<li><a href="LynxOS" title="LynxOS">LynxOS</a></li>

<li><i><a href="Multi-Environment_Real-Time" title="Multi-Environment Real-Time">Multi-Environment Real-Time</a></i>^ (<i>MERT</i> – <i>Unix-RT</i>)</li>

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<ul><li><i><a href="ChorusOS" title="ChorusOS">ChorusOS</a></i>^</li>

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<li><a href="Nucleus_RTOS" title="Nucleus RTOS">Nucleus RTOS</a>^</li>

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<ul><li><a href="Micro_T-Kernel" title="Micro T-Kernel">Micro T-Kernel</a></li>

<li><a href="T-Engine_Forum" title="T-Engine Forum">T-Engine Forum</a> (organization)</li>

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<li><i><a href="RTEMS" title="RTEMS">RTEMS</a>°</i></li></ul>

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<ul><li><i><a href="JavaOS#Chorus/Jazz" title="JavaOS">Chorus/Jazz</a></i>^ (<i><a href="JavaOS" title="JavaOS">JavaOS</a></i> + <i><a href="ChorusOS" title="ChorusOS">ChorusOS</a></i>^)</li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="DOS" title="DOS">DOS</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><i><a href="Multiuser_DOS" title="Multiuser DOS">Multiuser DOS</a></i>

<ul><li><i><a href="Concurrent_DOS" class="mw-redirect" title="Concurrent DOS">Concurrent DOS</a></i></li>

<li><i><a href="FlexOS" title="FlexOS">FlexOS</a></i></li>

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<ul><li><a href="L4Linux" title="L4Linux">L<sup>4</sup>Linux</a>^°</li>

<li><a href="PikeOS" title="PikeOS">PikeOS</a>^</li>

<li><a href="Wombat_(operating_system)" title="Wombat (operating system)">Wombat</a>^°</li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="Psion_(company)" title="Psion (company)">Psion</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><i><a href="EKA2" title="EKA2">EKA2</a></i>^° kernel → <i><a href="Symbian" title="Symbian">Symbian</a> OS</i>^°</li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="Microsoft" title="Microsoft">Microsoft</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><a href="ThreadX" title="ThreadX">ThreadX</a>^</li>

<li><a href="Windows_Embedded_Compact" class="mw-redirect" title="Windows Embedded Compact">Windows Embedded Compact</a></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="IBM" title="IBM">IBM</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em">

<li><a href="Transaction_Processing_Facility" title="Transaction Processing Facility">Transaction Processing Facility</a> (TPF)</li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="Texas_Instruments" title="Texas Instruments">Texas Instruments</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em">

<li><a href="TI-RTOS#RTOS_kernel_overview" title="TI-RTOS">TI-RTOS Kernel</a>^°</li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="Digital_Equipment_Corporation" title="Digital Equipment Corporation">DEC</a> <a href="PDP-11" title="PDP-11">PDP-11</a> & <a href="VAX" title="VAX">VAX</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em">

<li><i><a href="VAXELN" title="VAXELN">VAXELN</a></i></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Low resource</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><a href="ChibiOS/RT" title="ChibiOS/RT">ChibiOS/RT</a>^°</li>

<li><a href="Contiki" title="Contiki">Contiki</a>°</li>

<li><a href="ERIKA_Enterprise" title="ERIKA Enterprise">ERIKA Enterprise</a>°</li>

<li>FunkOS°</li>

<li><a href="Apache_Mynewt" title="Apache Mynewt">Mynewt</a>°</li>

<li><a href="OpenComRTOS" title="OpenComRTOS">OpenComRTOS</a>^</li>

<li><a href="RT-Thread" title="RT-Thread">RT-Thread</a>° Nano</li>

<li><a href="RTEMS" title="RTEMS">RTEMS</a>°</li>

<li><a href="ThreadX" title="ThreadX">ThreadX</a>^</li>

<li><a href="Zephyr_(operating_system)" title="Zephyr (operating system)">Zephyr</a>^°</li></ul>

</div></td></tr></tbody></table><div>

<ul><li><i><a href="BeRTOS" title="BeRTOS">BeRTOS</a></i>^°</li>

<li><i><a href="DioneOS" title="DioneOS">DioneOS</a></i></li>

<li><a href="Segger_Microcontroller_Systems" title="Segger Microcontroller Systems">embOS</a></li>

<li><a href="FreeRTOS" title="FreeRTOS">FreeRTOS</a>^°</li>

<li><a href="Green_Hills_Software#Real-time_operating_systems" title="Green Hills Software">µ-velOSity</a>^</li>

<li><a href="OS-9" title="OS-9">OS-9</a> (<a href="Microware" title="Microware">Microware</a>)</li>

<li><a href="Phantom_OS" title="Phantom OS">Phantom OS</a>^°</li>

<li><a href="RT-Thread" title="RT-Thread">RT-Thread</a>° Standard</li>

<li><a href="ScreenOS" title="ScreenOS">ScreenOS</a></li>

<li><i><a href="Sintran_III" title="Sintran III">Sintran III</a></i></li>

<li><i><a href="THEOS" title="THEOS">THEOS</a></i></li>

<li><i><a href="Thoth_(operating_system)" title="Thoth (operating system)">Thoth</a></i>^ → <i><a href="Harmony_(operating_system)" title="Harmony (operating system)">Harmony</a></i>^</li>

<li><a href="VxWorks" title="VxWorks">VxWorks</a></li>

<li><a href="EulerOS" title="EulerOS">UniProton</a></li></ul></div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="Software_framework" title="Software framework">Frameworks</a>, <a href="Software_development_kit" title="Software development kit">kits</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em">

<li><a href="Robot_Operating_System" title="Robot Operating System">Robot Operating System</a>° 2</li>

<li><a href="Xenomai" title="Xenomai">Xenomai</a>°</li>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="Programmer" title="Programmer">Developers</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><a href="Gordon_Bell_(QNX)" title="Gordon Bell (QNX)">Gordon Bell</a></li>

<li><a href="David_Cheriton" title="David Cheriton">David Cheriton</a></li>

<li><a href="Dave_Cutler" title="Dave Cutler">Dave Cutler</a></li>

<li><a href="Dan_Dodge" title="Dan Dodge">Dan Dodge</a></li>

<li><a href="Adam_Dunkels" title="Adam Dunkels">Adam Dunkels</a></li>

<li><a href="Ken_Sakamura" title="Ken Sakamura">Ken Sakamura</a></li></ul>

</div></td></tr><tr><td class="navbox-abovebelow" colspan="2"><div>

<ul><li><i>Italics</i> <b>= discontinued</b></li>

<li><b>^ = <a href="Microkernel" title="Microkernel">Microkernel</a></b></li>

<li><b>° = <a href="Open-source_software" title="Open-source software">Open-source software</a></b><br><span class="noviewer" typeof="mw:File"><span title="List-Class article"></span></span> <b><a href="Comparison_of_real-time_operating_systems" title="Comparison of real-time operating systems">Comparison</a></b> <span class="noviewer" typeof="mw:File"><span title="Category"></span></span> <b>Category</b></li></ul>

</div></td></tr></tbody></table></div>

<div class="navbox-styles"></div><div role="navigation" class="navbox" aria-labelledby="Microkernels-nanokernels667" style="padding:3px"><table class="nowraplinks hlist mw-collapsible autocollapse navbox-inner" style="border-spacing:0;background:transparent;color:inherit"><tbody><tr><th scope="col" class="navbox-title" colspan="2"><div id="Microkernels-nanokernels667" style="font-size:114%;margin:0 4em"><a href="Microkernel" title="Microkernel">Microkernels</a>-<a href="Microkernel#Nanokernel" title="Microkernel">nanokernels</a></div></th></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="Kernel_(operating_system)" title="Kernel (operating system)">Kernels</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:1%"><a href="L4_microkernel_family" title="L4 microkernel family">L4</a> family</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><i><a href="Eumel" title="Eumel">Eumel</a></i> → <i><a href="L3_microkernel" class="mw-redirect" title="L3 microkernel">L3</a></i> → <a href="L4_microkernel_family" title="L4 microkernel family">L4</a>°</li>

<ul><li><i><a href="Mac_OS_nanokernel" title="Mac OS nanokernel">Mac OS nanokernel</a></i></li>

<li><i><a href="NuKernel" class="mw-redirect" title="NuKernel">NuKernel</a></i></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="Psion_(company)" title="Psion (company)">Psion</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em">

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="Amiga" title="Amiga">Amiga</a>-type</th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><a href="Exec_(Amiga)#ExecSG" title="Exec (Amiga)">ExecSG</a></li></ul></li>

<li><a href="Quark_(kernel)" title="Quark (kernel)">Quark</a></li>

<li><i><a href="WarpOS" title="WarpOS">WarpOS</a></i></li></ul>

</div></td></tr></tbody></table><div>

<ul><li><i><a href="Adaptive_Domain_Environment_for_Operating_Systems" title="Adaptive Domain Environment for Operating Systems">ADEOS</a></i>°</li>

<li>Little Kernel</li>

<li><i><a href="Mach_(kernel)" title="Mach (kernel)">Mach</a></i>°

<li><i><a href="MicroEmpix" title="MicroEmpix">MicroEmpix</a></i></li>

<li><a href="Green_Hills_Software#Real-time_operating_systems" title="Green Hills Software">µ-velOSity</a>^</li>

<li><i><a href="Spring_(operating_system)#The_nucleus" title="Spring (operating system)">nucleus</a></i></li>

<li><i><a href="PowerUP_(accelerator)#PowerUP_software" title="PowerUP (accelerator)">PowerUP</a></i></li>

<li><a href="TI-RTOS#RTOS_kernel_overview" title="TI-RTOS">TI-RTOS kernel</a>^°</li>

<li><i><a href="Vanguard_(microkernel)" title="Vanguard (microkernel)">Vanguard</a></i></li></ul></div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="Operating_system" title="Operating system">Operating<br>systems</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:1%"><a href="POSIX" title="POSIX">POSIX</a> support</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:1%"><a href="Unix-like" title="Unix-like">Unix-like</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em">

<li><i><a href="Lites" title="Lites">Lites</a></i></li>

<li><i><a href="Meiko_Scientific#MeikOS" title="Meiko Scientific">MeikOS</a></i></li>

<li><a href="Minix" title="Minix">Minix</a>°

<ul><li><a href="Minix-vmd" class="mw-redirect" title="Minix-vmd">Minix-vmd</a>°</li>

<li><a href="Minix_3" title="Minix 3">Minix 3</a>°</li></ul></li>

<li><i><a href="MkLinux" title="MkLinux">MkLinux</a></i>°</li>

<li><i><a href="Multi-Environment_Real-Time" title="Multi-Environment Real-Time">Multi-Environment Real-Time</a></i>^ (<i>MERT</i> – <i>Unix-RT</i>)</li>

<li><a href="Redox_(operating_system)" class="mw-redirect" title="Redox (operating system)">Redox</a>°</li>

<li><i><a href="Spring_(operating_system)" title="Spring (operating system)">Spring</a></i></li>

<li><a href="Tinix" title="Tinix">Tinix</a></li>

<li><i><a href="UNICOS" title="UNICOS">UNICOS</a></i></li>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Partial</th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><i><a href="ChorusOS" title="ChorusOS">ChorusOS</a>^</i></li>

<li><a href="Integrity_(operating_system)" title="Integrity (operating system)">Integrity</a>^</li>

<li><a href="Nucleus_RTOS" title="Nucleus RTOS">Nucleus RTOS</a>^</li>

<li><a href="NuttX" title="NuttX">NuttX</a>^°</li>

</div></td></tr></tbody></table><div></div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="Capability-based_security" title="Capability-based security">Capability-based</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><i><a href="GNOSIS" title="GNOSIS">GNOSIS</a></i> → <i><a href="KeyKOS" title="KeyKOS">KeyKOS</a></i> → <i><a href="EROS_(microkernel)" title="EROS (microkernel)">EROS</a></i> → CapROS</li>

<li><i><a href="Hydra_(operating_system)" title="Hydra (operating system)">Hydra</a></i></li>

<li><i><a href="Midori_(operating_system)" title="Midori (operating system)">Midori</a></i></li>

<li><i><a href="NLTSS" title="NLTSS">NLTSS</a></i></li>

<li><i><a href="HarmonyOS_NEXT" title="HarmonyOS NEXT">HarmonyOS NEXT</a> (<a href="OpenHarmony" title="OpenHarmony">OpenHarmony</a>, <a href="OpenHarmony#Oniro_OS" title="OpenHarmony">Oniro OS</a>)</i> → <i><a href="HarmonyOS" title="HarmonyOS">HarmonyOS</a></i></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="L4_microkernel_family" title="L4 microkernel family">L4</a> kernel</th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><a href="L4Linux" title="L4Linux">L<sup>4</sup>Linux</a>^°</li>

<li><a href="PikeOS" title="PikeOS">PikeOS</a>^</li>

<li><a href="Wombat_(operating_system)" title="Wombat (operating system)">Wombat</a>^°</li></ul>

<ul><li><i><a href="JavaOS" title="JavaOS">JavaOS</a></i> (<i><a href="JavaOS#Chorus/Jazz" title="JavaOS">Chorus/Jazz</a></i>^ integrates <i><a href="ChorusOS" title="ChorusOS">ChorusOS</a></i>^)</li>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="Macintosh" class="mw-redirect" title="Macintosh">Macintosh</a> hosted</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th id="Unix-like13" scope="row" class="navbox-group" style="width:1%"><a href="Unix-like" title="Unix-like">Unix-like</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><i><a href="MachTen" title="MachTen">MachTen</a></i></li>

<li><i><a href="MacMach" title="MacMach">MacMach</a></i></li></ul>

</div></td></tr></tbody></table><div>

<ul><li><i><a href="Copland_(operating_system)" title="Copland (operating system)">Copland</a></i></li>

<li><i><a href="Mac_OS_8#Mac_OS_8.6" title="Mac OS 8">Classic Mac OS</a></i> (<a href="PowerPC" title="PowerPC">PowerPC</a> kernel)</li></ul></div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="Psion_(company)" title="Psion (company)">Psion</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em">

<li><i><a href="EPOC_(operating_system)" title="EPOC (operating system)">EPOC</a></i> → <i><a href="Symbian" title="Symbian">Symbian</a> OS</i>^°</li>

<ul><li><a href="AmigaOS" title="AmigaOS">AmigaOS</a></li>

<li><a href="AROS_Research_Operating_System" title="AROS Research Operating System">AROS</a>°

<ul><li><a href="AROS_Research_Operating_System#AspireOS" title="AROS Research Operating System">AspireOS</a>°</li>

<li><a href="AROS_Research_Operating_System#Broadway" title="AROS Research Operating System">Broadway</a>°</li>

<li><a href="AROS_Research_Operating_System#Icaros_Desktop" title="AROS Research Operating System">Icaros Desktop</a>°</li></ul></li>

<li><a href="MorphOS" title="MorphOS">MorphOS</a></li></ul>

<ul><li><a href="Singularity_(operating_system)" title="Singularity (operating system)">Singularity</a></li>

<li><a href="ThreadX" title="ThreadX">ThreadX</a>^°</li>

<li><i><a href="Verve_(operating_system)" title="Verve (operating system)">Verve</a></i></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="AIM_alliance" title="AIM alliance">AIM alliance</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><i>Pink</i> → <i><a href="Taligent" title="Taligent">Taligent</a> OS</i> → <i><a href="Workplace_OS" title="Workplace OS">Workplace OS</a></i></li></ul>

</div></td></tr></tbody></table><div>

<ul><li><i><a href="Amoeba_(operating_system)" title="Amoeba (operating system)">Amoeba</a></i>°</li>

<li><i><a href="BeRTOS" title="BeRTOS">BeRTOS</a></i>^°</li>

<li><a href="ChibiOS/RT" title="ChibiOS/RT">ChibiOS/RT</a>^°</li>

<li><a href="FreeRTOS" title="FreeRTOS">FreeRTOS</a>^°</li>

<li><a href="HelenOS" title="HelenOS">HelenOS</a>°</li>

<li><a href="OpenComRTOS" title="OpenComRTOS">OpenComRTOS</a>^</li>

<li><a href="Phantom_OS" title="Phantom OS">Phantom OS</a>^°</li>

<li><a href="SharpOS" title="SharpOS">SharpOS</a>°</li>

<li><i><a href="Thoth_(operating_system)" title="Thoth (operating system)">Thoth</a></i>^ → <i><a href="Harmony_(operating_system)" title="Harmony (operating system)">Harmony</a></i>^ → <i><a href="V_(operating_system)" title="V (operating system)">V</a></i></li>

<li><a href="Versatile_Real-Time_Executive" title="Versatile Real-Time Executive">VRTX</a>^</li></ul></div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="Software_framework" title="Software framework">Frameworks</a>, <a href="Software_development_kit" title="Software development kit">kits</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em">

<li><a href="Cosmos_(operating_system)" title="Cosmos (operating system)">Cosmos</a>°</li>

<li><a href="Genode" title="Genode">Genode</a>°</li>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="Programmer" title="Programmer">Developers</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><a href="Gordon_Bell_(QNX)" title="Gordon Bell (QNX)">Gordon Bell</a></li>

<li><a href="Thomas_Bushnell" title="Thomas Bushnell">Thomas Bushnell</a></li>

<li><a href="David_Cheriton" title="David Cheriton">David Cheriton</a></li>

<li><a href="Dan_Dodge" title="Dan Dodge">Dan Dodge</a></li>

<li><a href="Per_Brinch_Hansen" title="Per Brinch Hansen">Per Brinch Hansen</a></li>

<li><a href="Gernot_Heiser" title="Gernot Heiser">Gernot Heiser</a></li>

<li><a href="Jochen_Liedtke" title="Jochen Liedtke">Jochen Liedtke</a></li>

<li><a href="James_G._Mitchell" title="James G. Mitchell">James G. Mitchell</a></li>

<li><a href="Ike_Nassi" title="Ike Nassi">Ike Nassi</a></li>

<li><a href="Richard_Rashid" title="Richard Rashid">Richard Rashid</a></li>

<li><a href="Andrew_S._Tanenbaum" title="Andrew S. Tanenbaum">Andrew S. Tanenbaum</a></li>

<li><a href="Avie_Tevanian" title="Avie Tevanian">Avie Tevanian</a></li>

<li><a href="William_Wulf" title="William Wulf">William Wulf</a></li></ul>

</div></td></tr><tr><td class="navbox-abovebelow" colspan="2"><div>

<ul><li><i>Italics</i> <b>= discontinued</b></li>

<li><b>° = <a href="Open-source_software" title="Open-source software">Open-source software</a></b><br><span class="noviewer" typeof="mw:File"><span title="Category"></span></span> <b>Category: Microkernel-based operating systems</b> <span class="noviewer" typeof="mw:File"><span title="Category"></span></span> <b>Category: Microkernels</b></li></ul>

</div></td></tr></tbody></table></div></div><div><div class="zim-footer">

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