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<title>Process (computing)</title>

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<span id="openzim-page-title" class="mw-page-title-main"><span class="mw-page-title-main">Process (computing)</span></span>

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<p>In <a href="Computing" title="Computing">computing</a>, a <b>process</b> is the <a href="Instance_(computer_science)" title="Instance (computer science)">instance</a> of a <a href="Computer_program" title="Computer program">computer program</a> that is being executed by one or many <a href="Thread_(computing)" title="Thread (computing)">threads</a>. There are many different process models, some of which are light weight, but almost all processes (even entire <a href="Virtual_machine" title="Virtual machine">virtual machines</a>) are rooted in an <a href="Operating_system" title="Operating system">operating system</a> (OS) process which comprises the program code, assigned system resources, physical and logical access permissions, and data structures to initiate, control and coordinate execution activity. Depending on the OS, a process may be made up of multiple threads of execution that execute instructions <a href="Concurrency_(computer_science)" title="Concurrency (computer science)">concurrently</a>.<sup id="cite_ref-OSC_Chap4_1-0" class="reference"><a href="#cite_note-OSC_Chap4-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Vah96_2-0" class="reference"><a href="#cite_note-Vah96-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup>

</p><p>While a computer program is a passive collection of <a href="Instruction_set" class="mw-redirect" title="Instruction set">instructions</a> typically stored in a file on disk, a process is the execution of those instructions after being loaded from the disk into memory. Several processes may be associated with the same program; for example, opening up several instances of the same program often results in more than one process being executed.

</p><p><a href="Computer_multitasking" title="Computer multitasking">Multitasking</a> is a method to allow multiple processes to share <a href="Central_processing_unit" title="Central processing unit">processors</a> (CPUs) and other system resources. Each CPU (core) executes a single process at a time. However, multitasking allows each processor to <a href="Context_switch" title="Context switch">switch</a> between tasks that are being executed without having to wait for each task to finish (<a href="Preemption_(computing)" title="Preemption (computing)">preemption</a>). Depending on the operating system implementation, switches could be performed when tasks initiate and wait for completion of <a href="Input/output" title="Input/output">input/output</a> operations, when a task voluntarily yields the CPU, on hardware <a href="Interrupt" title="Interrupt">interrupts</a>, and when the operating system scheduler decides that a process has expired its fair share of CPU time (e.g, by the <a href="Completely_Fair_Scheduler" title="Completely Fair Scheduler">Completely Fair Scheduler</a> of the <a href="Linux_kernel" title="Linux kernel">Linux kernel</a>).

</p><p>A common form of multitasking is provided by CPU's <a href="Time-sharing" title="Time-sharing">time-sharing</a> that is a method for interleaving the execution of users' processes and threads, and even of independent kernel tasks – although the latter feature is feasible only in preemptive <a href="Kernel_(operating_system)" title="Kernel (operating system)">kernels</a> such as <a href="Linux_kernel" title="Linux kernel">Linux</a>. Preemption has an important side effect for interactive processes that are given higher priority with respect to CPU bound processes, therefore users are immediately assigned computing resources at the simple pressing of a key or when moving a mouse. Furthermore, applications like video and music reproduction are given some kind of real-time priority, preempting any other lower priority process. In time-sharing systems, <a href="Context_switch" title="Context switch">context switches</a> are performed rapidly, which makes it seem like multiple processes are being executed simultaneously on the same processor. This seemingly-simultaneous execution of multiple processes is called <a href="Concurrency_(computer_science)" title="Concurrency (computer science)">concurrency</a>.

</p><p>For security and reliability, most modern <a href="Operating_system" title="Operating system">operating systems</a> prevent direct <a href="Inter-process_communication" title="Inter-process communication">communication</a> between independent processes, providing strictly mediated and controlled inter-process communication.

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

<p>In general, a computer system process consists of (or is said to <i>own</i>) the following resources:

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<ul><li>An <i>image</i> of the executable <a href="Machine_code" title="Machine code">machine code</a> associated with a program.</li>

<li>Memory (typically some region of <a href="Virtual_memory" title="Virtual memory">virtual memory</a>); which includes the executable code, process-specific data (input and output), a <a href="Call_stack" title="Call stack">call stack</a> (to keep track of active <a href="Subroutine" class="mw-redirect" title="Subroutine">subroutines</a> and/or other events), and a <a href="Heap_memory" class="mw-redirect" title="Heap memory">heap</a> to hold intermediate computation data generated during run time.</li>

<li>Operating system descriptors of resources that are allocated to the process, such as <a href="File_descriptor" title="File descriptor">file descriptors</a> (<a href="Unix" title="Unix">Unix</a> terminology) or <a href="Handle_(computing)" title="Handle (computing)">handles</a> (<a href="Microsoft_Windows" title="Microsoft Windows">Windows</a>), and data sources and sinks.</li>

<li><a href="Computer_security" title="Computer security">Security</a> attributes, such as the process owner and the process' set of permissions (allowable operations).</li>

<li><a href="Central_processing_unit" title="Central processing unit">Processor</a> state (<a href="Context_(computing)" title="Context (computing)">context</a>), such as the content of <a href="Processor_register" title="Processor register">registers</a> and physical memory addressing. The <i>state</i> is typically stored in computer registers when the process is executing, and in memory otherwise.<sup id="cite_ref-OSC_Chap4_1-1" class="reference"><a href="#cite_note-OSC_Chap4-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup></li></ul>

<p>The operating system holds most of this information about active processes in data structures called <a href="Process_control_block" title="Process control block">process control blocks</a>. Any subset of the resources, typically at least the processor state, may be associated with each of the process' <a href="Thread_(computer_science)" class="mw-redirect" title="Thread (computer science)">threads</a> in operating systems that support threads or <i>child</i> processes.

</p><p>The operating system keeps its processes separate and allocates the resources they need, so that they are less likely to interfere with each other and cause system failures (e.g., <a href="Deadlock_(computer_science)" title="Deadlock (computer science)">deadlock</a> or <a href="Thrashing_(computer_science)" title="Thrashing (computer science)">thrashing</a>). The operating system may also provide mechanisms for <a href="Inter-process_communication" title="Inter-process communication">inter-process communication</a> to enable processes to interact in safe and predictable ways.

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<div class="mw-heading mw-heading2"><h2 id="Multitasking_and_process_management">Multitasking and process management</h2></div>

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</style><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="Process_management_(computing)" title="Process management (computing)">Process management (computing)</a></div>

<p>A <a href="Computer_multitasking" title="Computer multitasking">multitasking</a> <a href="Operating_system" title="Operating system">operating system</a> may just switch between processes to give the appearance of many processes <a href="Execution_(computing)" title="Execution (computing)">executing</a> simultaneously (that is, in <a href="Parallel_computing" title="Parallel computing">parallel</a>), though in fact only one process can be executing at any one time on a single <a href="Central_processing_unit" title="Central processing unit">CPU</a> (unless the CPU has multiple cores, then <a href="Multithreading_(computer_architecture)" title="Multithreading (computer architecture)">multithreading</a> or other similar technologies can be used).<sup id="cite_ref-3" class="reference"><a href="#cite_note-3"><span class="cite-bracket">[</span>a<span class="cite-bracket">]</span></a></sup>

</p><p>It is usual to associate a single process with a main program, and child processes with any spin-off, parallel processes, which behave like <a href="Asynchrony_(computer_programming)" title="Asynchrony (computer programming)">asynchronous</a> subroutines. A process is said to <i>own</i> resources, of which an <i>image</i> of its program (in memory) is one such resource. However, in multiprocessing systems <i>many</i> processes may run off of, or share, the same <a href="Reentrancy_(computing)" title="Reentrancy (computing)">reentrant</a> program at the same location in memory, but each process is said to own its own <i>image</i> of the program.

</p><p>Processes are often called "tasks" in <a href="Embedded_system" title="Embedded system">embedded</a> operating systems. The sense of "process" (or task) is "something that takes up time", as opposed to "memory", which is "something that takes up space".<sup id="cite_ref-4" class="reference"><a href="#cite_note-4"><span class="cite-bracket">[</span>b<span class="cite-bracket">]</span></a></sup>

</p><p>The above description applies to both processes managed by an operating system, and processes as defined by <a href="Process_calculus" title="Process calculus">process calculi</a>.

</p><p>If a process requests something for which it must wait, it will be blocked. When the process is in the <a href="Process_state" title="Process state">blocked state</a>, it is eligible for swapping to disk, but this is transparent in a <a href="Virtual_memory" title="Virtual memory">virtual memory</a> system, where regions of a process's memory may be really on disk and not in <a href="Computer_data_storage#Primary_storage" title="Computer data storage">main memory</a> at any time. Even portions of active processes/tasks (executing programs) are eligible for swapping to disk, if the portions have not been used recently. Not all parts of an executing program and its data have to be in physical memory for the associated process to be active.

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<div class="mw-heading mw-heading3"><h3 id="Process_states">Process states</h3></div>

<div role="note" class="hatnote navigation-not-searchable">Main article: <a href="Process_state" title="Process state">Process state</a></div>

<p>An operating system <a href="Kernel_(operating_system)" title="Kernel (operating system)">kernel</a> that allows multitasking needs processes to have <a href="Process_states" class="mw-redirect" title="Process states">certain states</a>. Names for these states are not standardised, but they have similar functionality.<sup id="cite_ref-OSC_Chap4_1-2" class="reference"><a href="#cite_note-OSC_Chap4-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup>

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<ul><li>First, the process is "created" by being loaded from a <a href="Auxiliary_memory" class="mw-redirect" title="Auxiliary memory">secondary storage</a> device (<a href="Hard_disk_drive" title="Hard disk drive">hard disk drive</a>, <a href="CD-ROM" title="CD-ROM">CD-ROM</a>, etc.) into <a href="Main_memory" class="mw-redirect" title="Main memory">main memory</a>. After that the <a href="Scheduling_(computing)" title="Scheduling (computing)">process scheduler</a> assigns it the "waiting" state.</li>

<li>While the process is "waiting", it waits for the <a href="Scheduling_(computing)" title="Scheduling (computing)">scheduler</a> to do a so-called <a href="Context_switch" title="Context switch">context switch</a>. The context switch loads the process into the processor and changes the state to "running" while the previously "running" process is stored in a "waiting" state.</li>

<li>If a process in the "running" state needs to wait for a resource (wait for user input or file to open, for example), it is assigned the "blocked" state. The process state is changed back to "waiting" when the process no longer needs to wait (in a blocked state).</li>

<li>Once the process finishes execution, or is terminated by the operating system, it is no longer needed. The process is removed instantly or is moved to the "terminated" state. When removed, it just waits to be removed from main memory.<sup id="cite_ref-OSC_Chap4_1-3" class="reference"><a href="#cite_note-OSC_Chap4-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Stallings_5-0" class="reference"><a href="#cite_note-Stallings-5"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup></li></ul>

<div class="mw-heading mw-heading2"><h2 id="Inter-process_communication">Inter-process communication</h2></div>

<div role="note" class="hatnote navigation-not-searchable">Main article: <a href="Inter-process_communication" title="Inter-process communication">Inter-process communication</a></div>

<p>When processes need to communicate with each other they must share parts of their <a href="Address_space" title="Address space">address spaces</a> or use other forms of inter-process communication (IPC).

For instance in a <a href="Shell_(computing)" title="Shell (computing)">shell</a> <a href="Pipeline_(computing)" title="Pipeline (computing)">pipeline</a>, the output of the first process needs to pass to the second one, and so on. Another example is a task that has been decomposed into cooperating but partially independent processes which can run simultaneously (i.e., using concurrency, or true parallelism – the latter model is a particular case of concurrent execution and is feasible whenever multiple CPU cores are available for the processes that are ready to run).

</p><p>It is even possible for two or more processes to be running on different machines that may run different operating system (OS), therefore some mechanisms for communication and synchronization (called <a href="Communications_protocol" class="mw-redirect" title="Communications protocol">communications protocols</a> for distributed computing) are needed (e.g., the <a href="Message_Passing_Interface" title="Message Passing Interface">Message Passing Interface</a> {MPI}).

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

<div role="note" class="hatnote navigation-not-searchable">See also: <a href="History_of_operating_systems" title="History of operating systems">History of operating systems</a></div>

<p>By the early 1960s, computer control software had evolved from monitor control software, for example <a href="IBM_7090/94_IBSYS" title="IBM 7090/94 IBSYS">IBSYS</a>, to executive control software. Over time, computers got faster while <a href="Time-sharing" title="Time-sharing">computer time</a> was still neither cheap nor fully utilized; such an environment made <a href="Computer_multitasking#Multiprogramming" title="Computer multitasking">multiprogramming</a> possible and necessary. Multiprogramming means that several programs run <a href="Concurrency_(computer_science)" title="Concurrency (computer science)">concurrently</a>. At first, more than one program ran on a single processor, as a result of underlying <a href="Uniprocessor_system" title="Uniprocessor system">uniprocessor</a> computer architecture, and they shared scarce and limited hardware resources; consequently, the concurrency was of a <i>serial</i> nature. On later systems with <a href="Multiprocessing" title="Multiprocessing">multiple processors</a>, multiple programs may run concurrently in <i><a href="Parallel_computing" title="Parallel computing">parallel</a></i>.

</p><p>Programs consist of sequences of instructions for processors. A single processor can run only one instruction at a time: it is impossible to run more programs at the same time. A program might need some <a href="System_resource" title="System resource">resource</a>, such as an input device, which has a large delay, or a program might start some slow operation, such as sending output to a printer. This would lead to processor being "idle" (unused). To keep the processor busy at all times, the execution of such a program is halted and the operating system switches the processor to run another program. To the user, it will appear that the programs run at the same time (hence the term "parallel").

</p><p>Shortly thereafter, the notion of a "program" was expanded to the notion of an "executing program and its context". The concept of a process was born, which also became necessary with the invention of <a href="Reentrancy_(computing)" title="Reentrancy (computing)">re-entrant code</a>. <a href="Thread_(computer_science)" class="mw-redirect" title="Thread (computer science)">Threads</a> came somewhat later. However, with the advent of concepts such as <a href="Time-sharing" title="Time-sharing">time-sharing</a>, <a href="Computer_network" title="Computer network">computer networks</a>, and multiple-CPU <a href="Shared_memory" title="Shared memory">shared memory</a> computers, the old "multiprogramming" gave way to true <a href="Computer_multitasking" title="Computer multitasking">multitasking</a>, <a href="Multiprocessing" title="Multiprocessing">multiprocessing</a> and, later, <a href="Multithreading_(computer_architecture)" title="Multithreading (computer architecture)">multithreading</a>.

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<ul><li><a href="Background_process" title="Background process">Background process</a></li>

<li><a href="Child_process" title="Child process">Child process</a></li>

<li><a href="Light-weight_process" title="Light-weight process">Light-weight process</a></li>

<li><a href="Orphan_process" title="Orphan process">Orphan process</a></li>

<li><a href="Parent_process" title="Parent process">Parent process</a></li>

<li><a href="Process_group" title="Process group">Process group</a></li>

<li><a href="Working_directory" title="Working directory">Working directory</a></li>

<li><a href="Zombie_process" title="Zombie process">Zombie process</a></li></ul>

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

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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">Some modern CPUs combine two or more independent processors in a <a href="Multi-core_processor" title="Multi-core processor">multi-core</a> configuration and can execute several processes simultaneously. Another technique called <a href="Simultaneous_multithreading" title="Simultaneous multithreading">simultaneous multithreading</a> (used in <a href="Intel" title="Intel">Intel</a>'s <a href="Hyper-threading" title="Hyper-threading">Hyper-threading</a> technology) can simulate simultaneous execution of multiple processes or threads.</span>

</li>

<li id="cite_note-4"><span class="mw-cite-backlink"><b><a href="#cite_ref-4">^</a></b></span> <span class="reference-text">Tasks and processes refer essentially to the same entity. And, although they have somewhat different terminological histories, they have come to be used as synonyms. Today, the term process is generally preferred over task, except when referring to "multitasking", since the alternative term, "multiprocessing", is too easy to confuse with multiprocessor (which is a computer with two or more CPUs).</span>

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

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</style><cite id="CITEREFSilberschatzCagneGalvin2004" class="citation book cs1"><a href="Abraham_Silberschatz" title="Abraham Silberschatz">Silberschatz, Abraham</a>; Cagne, Greg; Galvin, Peter Baer (2004). "Chapter 4. Processes". <i>Operating system concepts with Java</i> (Sixth ed.). <a href="John_Wiley_%26_Sons" class="mw-redirect" title="John Wiley & Sons">John Wiley & Sons</a>. <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <bdi>0-471-48905-0</bdi>.</cite></span>

</li>

<li id="cite_note-Vah96-2"><span class="mw-cite-backlink"><b><a href="#cite_ref-Vah96_2-0">^</a></b></span> <span class="reference-text"><cite id="CITEREFVahalia1996" class="citation book cs1">Vahalia, Uresh (1996). "Chapter 2. The Process and the Kernel". <span class="id-lock-registration" title="Free registration required"><a rel="nofollow" class="external text" href="https://archive.org/details/unixinternalsnew00vaha"><i>UNIX Internals: The New Frontiers</i></a></span>. Prentice-Hall Inc. <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <bdi>0-13-101908-2</bdi>.</cite></span>

</li>

<li id="cite_note-Stallings-5"><span class="mw-cite-backlink"><b><a href="#cite_ref-Stallings_5-0">^</a></b></span> <span class="reference-text"><cite id="CITEREFStallings2005" class="citation book cs1">Stallings, William (2005). <i>Operating Systems: internals and design principles</i> (5th ed.). Prentice Hall. <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <bdi>0-13-127837-1</bdi>.</cite> (particularly chapter 3, section 3.2, "process states", including figure 3.9 "process state transition with suspend states")</span>

</li>

</ol></div>

<div class="mw-heading mw-heading2"><h2 id="Further_reading">Further reading</h2></div>

<ul><li>Remzi H. Arpaci-Dusseau and Andrea C. Arpaci-Dusseau (2014). "<a rel="nofollow" class="external text" href="https://web.archive.org/web/20200916133128/https://pages.cs.wisc.edu/~remzi/OSTEP/">Operating Systems: Three Easy Pieces</a>". Arpaci-Dusseau Books. Relevant chapters: <a rel="nofollow" class="external text" href="https://web.archive.org/web/20200916133128/https://pages.cs.wisc.edu/~remzi/OSTEP/cpu-intro.pdf">Abstraction: The Process</a> <a rel="nofollow" class="external text" href="https://web.archive.org/web/20200916133128/https://pages.cs.wisc.edu/~remzi/OSTEP/cpu-api.pdf">The Process API</a></li>

<li>Gary D. Knott (1974) <i><a rel="nofollow" class="external text" href="http://doi.acm.org/10.1145/775280.775282">A proposal for certain process management and intercommunication primitives</a></i> ACM SIGOPS Operating Systems Review. Volume 8, Issue 4 (October 1974). pp. 7 – 44</li></ul>

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

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<div class="side-box-text plainlist">Wikiversity has learning resources about <i><b><a href="https://en.wikiversity.org/wiki/Processes_and_Threads" class="extiw external" title="v:Processes and Threads">Processes and Threads</a></b></i> at <div style="margin-left: 10px;"><a href="https://en.wikiversity.org/wiki/Operating_Systems/Process_and_Thread" class="extiw external" title="v:Operating Systems/Process and Thread">Operating Systems/Process and Thread</a></div></div></div>

</div>

<ul><li><span class="noviewer" typeof="mw:File"></span> Media related to <a href="https://commons.wikimedia.org/wiki/Category:Process_(computing)" class="extiw external" title="commons:Category:Process (computing)">Process (computing)</a> at Wikimedia Commons</li>

<li><a rel="nofollow" class="external text" href="http://www.processlibrary.com/">Online Resources For Process Information</a></li>

<li><a rel="nofollow" class="external text" href="http://www.file.net/">Computer Process Information Database and Forum</a></li>

<li><a rel="nofollow" class="external text" href="https://osnote.space/process-models-with-process-creation-termination-methods.html">Process Models with Process Creation & Termination Methods</a> <a rel="nofollow" class="external text" href="https://web.archive.org/web/20210206000025/https://osnote.space/process-models-with-process-creation-termination-methods.html">Archived</a> 2021-02-06 at the <a href="Wayback_Machine" title="Wayback Machine">Wayback Machine</a></li></ul>

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</style><div id="Parallel_computing346" style="font-size:114%;margin:0 4em"><a href="Parallel_computing" title="Parallel computing">Parallel computing</a></div></th></tr><tr><th scope="row" class="navbox-group" style="width:1%">General</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="Distributed_computing" title="Distributed computing">Distributed computing</a></li>

<li><a href="Parallel_computing" title="Parallel computing">Parallel computing</a></li>

<li><a href="Parallel_algorithm" title="Parallel algorithm">Parallel algorithm</a></li>

<li><a href="Massively_parallel" title="Massively parallel">Massively parallel</a></li>

<li><a href="Cloud_computing" title="Cloud computing">Cloud computing</a></li>

<li><a href="High-performance_computing" title="High-performance computing">High-performance computing</a></li>

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

<li><a href="Manycore_processor" title="Manycore processor">Manycore processor</a></li>

<li><a href="General-purpose_computing_on_graphics_processing_units" title="General-purpose computing on graphics processing units">GPGPU</a></li>

<li><a href="Computer_network" title="Computer network">Computer network</a></li>

<li><a href="Systolic_array" title="Systolic array">Systolic array</a></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Levels</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="Instruction-level_parallelism" title="Instruction-level parallelism">Instruction</a></li>

<li><a href="Task_parallelism" title="Task parallelism">Thread</a></li>

<li><a href="Memory-level_parallelism" title="Memory-level parallelism">Memory</a></li>

<li><a href="Pipeline_(computing)" title="Pipeline (computing)">Pipeline</a></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="Multithreading_(computer_architecture)" title="Multithreading (computer architecture)">Multithreading</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="Temporal_multithreading" title="Temporal multithreading">Temporal</a></li>

<li><a href="Simultaneous_multithreading" title="Simultaneous multithreading">Simultaneous</a> (SMT)</li>

<li><a href="Simultaneous_and_heterogeneous_multithreading" title="Simultaneous and heterogeneous multithreading">Simultaneous and heterogenous</a></li>

<li><a href="Speculative_multithreading" title="Speculative multithreading">Speculative</a> (SpMT)</li>

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

<li><a href="Computer_multitasking#Cooperative_multitasking" title="Computer multitasking">Cooperative</a></li>

<li><a href="Bulldozer_(microarchitecture)#Bulldozer_core" title="Bulldozer (microarchitecture)">Clustered multi-thread</a> (CMT)</li>

<li><a href="Hardware_scout" title="Hardware scout">Hardware scout</a></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Theory</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="Parallel_RAM" title="Parallel RAM">PRAM model</a></li>

<li><a href="Parallel_external_memory" title="Parallel external memory">PEM model</a></li>

<li><a href="Analysis_of_parallel_algorithms" title="Analysis of parallel algorithms">Analysis of parallel algorithms</a></li>

<li><a href="Amdahl's_law" title="Amdahl's law">Amdahl's law</a></li>

<li><a href="Gustafson's_law" title="Gustafson's law">Gustafson's law</a></li>

<li><a href="Cost_efficiency" title="Cost efficiency">Cost efficiency</a></li>

<li><a href="Karp%E2%80%93Flatt_metric" title="Karp–Flatt metric">Karp–Flatt metric</a></li>

<li><a href="Parallel_slowdown" title="Parallel slowdown">Slowdown</a></li>

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

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Elements</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="Thread_(computing)" title="Thread (computing)">Thread</a></li>

<li><a href="Fiber_(computer_science)" title="Fiber (computer science)">Fiber</a></li>

<li><a href="Instruction_window" title="Instruction window">Instruction window</a></li>

<li><a href="Array_(data_structure)" title="Array (data structure)">Array</a></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Coordination</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="Multiprocessing" title="Multiprocessing">Multiprocessing</a></li>

<li><a href="Memory_coherence" title="Memory coherence">Memory coherence</a></li>

<li><a href="Cache_coherence" title="Cache coherence">Cache coherence</a></li>

<li><a href="Cache_invalidation" title="Cache invalidation">Cache invalidation</a></li>

<li><a href="Barrier_(computer_science)" title="Barrier (computer science)">Barrier</a></li>

<li><a href="Synchronization_(computer_science)" title="Synchronization (computer science)">Synchronization</a></li>

<li><a href="Application_checkpointing" title="Application checkpointing">Application checkpointing</a></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="Computer_programming" title="Computer programming">Programming</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="Stream_processing" title="Stream processing">Stream processing</a></li>

<li><a href="Dataflow_programming" title="Dataflow programming">Dataflow programming</a></li>

<li><a href="Parallel_programming_model" title="Parallel programming model">Models</a>

<ul><li><a href="Implicit_parallelism" title="Implicit parallelism">Implicit parallelism</a></li>

<li><a href="Explicit_parallelism" title="Explicit parallelism">Explicit parallelism</a></li>

<li><a href="Concurrency_(computer_science)" title="Concurrency (computer science)">Concurrency</a></li></ul></li>

<li><a href="Non-blocking_algorithm" title="Non-blocking algorithm">Non-blocking algorithm</a></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="Computer_hardware" title="Computer hardware">Hardware</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="Flynn's_taxonomy" title="Flynn's taxonomy">Flynn's taxonomy</a>

<ul><li><a href="Single_instruction%2C_multiple_threads" title="Single instruction, multiple threads">Array processing</a> (SIMT)</li>

<li><a href="Flynn's_taxonomy#Pipelined_processor" title="Flynn's taxonomy">Pipelined processing</a></li>

<li><a href="Flynn's_taxonomy#Associative_processor" title="Flynn's taxonomy">Associative processing</a></li></ul></li>

<li><a href="Dataflow_architecture" title="Dataflow architecture">Dataflow architecture</a></li>

<li><a href="Instruction_pipelining" title="Instruction pipelining">Pipelined processor</a></li>

<li><a href="Superscalar_processor" title="Superscalar processor">Superscalar processor</a></li>

<li><a href="Vector_processor" title="Vector processor">Vector processor</a></li>

<li><a href="Multiprocessing" title="Multiprocessing">Multiprocessor</a>

<ul><li><a href="Symmetric_multiprocessing" title="Symmetric multiprocessing">symmetric</a></li>

<li><a href="Asymmetric_multiprocessing" title="Asymmetric multiprocessing">asymmetric</a></li></ul></li>

<li><a href="Semiconductor_memory" title="Semiconductor memory">Memory</a>

<ul><li><a href="Shared_memory" title="Shared memory">shared</a></li>

<li><a href="Distributed_memory" title="Distributed memory">distributed</a></li>

<li><a href="Distributed_shared_memory" title="Distributed shared memory">distributed shared</a></li>

<li><a href="Massively_parallel" title="Massively parallel">Massively parallel</a> computer</li>

<li><a href="Computer_cluster" title="Computer cluster">Computer cluster</a>

<ul><li><a href="Beowulf_cluster" title="Beowulf cluster">Beowulf cluster</a></li></ul></li>

<li><a href="Grid_computing" title="Grid computing">Grid computer</a></li>

<li><a href="Hardware_acceleration" title="Hardware acceleration">Hardware acceleration</a></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="API" title="API">APIs</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="Ateji_PX" title="Ateji PX">Ateji PX</a></li>

<li><a href="Boost_(C%2B%2B_libraries)" title="Boost (C++ libraries)">Boost</a></li>

<li><a href="Chapel_(programming_language)" title="Chapel (programming language)">Chapel</a></li>

<li><a href="Charm%2B%2B" title="Charm++">Charm++</a></li>

<li><a href="Coarray_Fortran" title="Coarray Fortran">Coarray Fortran</a></li>

<li><a href="Dryad_(programming)" title="Dryad (programming)">Dryad</a></li>

<li><a href="Global_Arrays" title="Global Arrays">Global Arrays</a></li>

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

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

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

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

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

<li><a href="Parallel_Extensions" title="Parallel Extensions">Parallel Extensions</a></li>

<li><a href="Pthreads" title="Pthreads">pthreads</a></li>

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

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Problems</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="Automatic_parallelization" title="Automatic parallelization">Automatic parallelization</a></li>

<li><a href="Deadlock_(computer_science)" title="Deadlock (computer science)">Deadlock</a></li>

<li><a href="Deterministic_algorithm" title="Deterministic algorithm">Deterministic algorithm</a></li>

<li><a href="Embarrassingly_parallel" title="Embarrassingly parallel">Embarrassingly parallel</a></li>

<li><a href="Parallel_slowdown" title="Parallel slowdown">Parallel slowdown</a></li>

<li><a href="Race_condition" title="Race condition">Race condition</a></li>

<li><a href="Software_lockout" title="Software lockout">Software lockout</a></li>

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

<li><a href="Starvation_(computer_science)" title="Starvation (computer science)">Starvation</a></li></ul>

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

<ul><li><span class="noviewer" typeof="mw:File"><span title="Category"></span></span> Category: Parallel computing</li></ul>

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

<div class="navbox-styles"></div><div role="navigation" class="navbox" aria-labelledby="Operating_systems310" style="padding:3px"><table class="nowraplinks 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="Operating_systems310" style="font-size:114%;margin:0 4em"><a href="Operating_system" title="Operating system">Operating systems</a></div></th></tr><tr><th scope="row" class="navbox-group" style="width:1%">General</th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><a href="Comparison_of_operating_systems" title="Comparison of operating systems">Comparison</a></li>

<li><a href="Forensic_software_engineering" title="Forensic software engineering">Forensic engineering</a></li>

<li><a href="History_of_operating_systems" title="History of operating systems">History</a></li>

<li><a href="Timeline_of_operating_systems" title="Timeline of operating systems">Timeline</a></li>

<li><a href="Usage_share_of_operating_systems" title="Usage share of operating systems">Usage share</a></li>

<li><a href="Comparison_of_user_features_of_operating_systems" title="Comparison of user features of operating systems">User features comparison</a></li></ul>

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

<ul><li><a href="Disk_operating_system" title="Disk operating system">Disk operating system</a></li>

<li><a href="Distributed_operating_system" title="Distributed operating system">Distributed operating system</a></li>

<li><a href="Embedded_operating_system" title="Embedded operating system">Embedded operating system</a></li>

<li><a href="Hobbyist_operating_system" title="Hobbyist operating system">Hobbyist operating system</a></li>

<li><a href="Just_enough_operating_system" title="Just enough operating system">Just enough operating system</a></li>

<li><a href="Mobile_operating_system" title="Mobile operating system">Mobile operating system</a></li>

<li><a href="Network_operating_system" title="Network operating system">Network operating system</a></li>

<li><a href="Object-oriented_operating_system" title="Object-oriented operating system">Object-oriented operating system</a></li>

<li><a href="Real-time_operating_system" title="Real-time operating system">Real-time operating system</a></li>

<li><a href="Supercomputer_operating_system" title="Supercomputer operating system">Supercomputer operating system</a></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="Kernel_(operating_system)" title="Kernel (operating system)">Kernel</a></th><td class="navbox-list-with-group navbox-list navbox-odd hlist" 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:6em"><a href="Computer_architecture" title="Computer architecture">Architectures</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="padding:0"><div style="padding:0 0.25em">

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

<li><a href="Hybrid_kernel" title="Hybrid kernel">Hybrid</a></li>

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

<li><a href="Monolithic_kernel" title="Monolithic kernel">Monolithic</a></li>

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

<li><a href="Vkernel" title="Vkernel">vkernel</a></li>

<li><a href="Rump_kernel" title="Rump kernel">Rump kernel</a></li>

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

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:6em">Components</th><td class="navbox-list-with-group navbox-list navbox-even" style="padding:0"><div style="padding:0 0.25em">

<ul><li><a href="Device_driver" title="Device driver">Device driver</a></li>

<li><a href="Loadable_kernel_module" title="Loadable kernel module">Loadable kernel module</a></li>

<li><a href="User_space_and_kernel_space" title="User space and kernel space">User space and kernel space</a></li></ul>

</div></td></tr></tbody></table><div></div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="Process_management_(computing)" title="Process management (computing)">Process management</a></th><td class="navbox-list-with-group navbox-list navbox-odd hlist" 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:6em">Concepts</th><td class="navbox-list-with-group navbox-list navbox-odd" style="padding:0"><div style="padding:0 0.25em">

<ul><li><a href="Computer_multitasking" title="Computer multitasking">Computer multitasking</a> (<a href="Cooperative_multitasking" title="Cooperative multitasking">Cooperative</a>, <a href="Preemption_(computing)" title="Preemption (computing)">Preemptive</a>)</li>

<li><a href="Context_switch" title="Context switch">Context switch</a></li>

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

<li><a href="Process_control_block" title="Process control block">Process control block</a></li>

<li><a href="Thread_(computing)" title="Thread (computing)">Thread</a></li>

<li><a href="Time-sharing" title="Time-sharing">Time-sharing</a></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:6em"><a href="Scheduling_(computing)" title="Scheduling (computing)">Scheduling<br>algorithms</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="padding:0"><div style="padding:0 0.25em">

<ul><li><a href="Fixed-priority_pre-emptive_scheduling" title="Fixed-priority pre-emptive scheduling">Fixed-priority preemptive</a></li>

<li><a href="Multilevel_feedback_queue" title="Multilevel feedback queue">Multilevel feedback queue</a></li>

<li><a href="Round-robin_scheduling" title="Round-robin scheduling">Round-robin</a></li>

<li><a href="Shortest_job_next" title="Shortest job next">Shortest job next</a></li></ul>

</div></td></tr></tbody></table><div></div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="Memory_management_(operating_systems)" title="Memory management (operating systems)">Memory management</a>,<br><a href="System_resource" title="System resource">resource</a> protection</th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><a href="Bus_error" title="Bus error">Bus error</a></li>

<li><a href="General_protection_fault" title="General protection fault">General protection fault</a></li>

<li><a href="Memory_paging" title="Memory paging">Memory paging</a></li>

<li><a href="Memory_protection" title="Memory protection">Memory protection</a></li>

<li><a href="Protection_ring" title="Protection ring">Protection ring</a></li>

<li><a href="Segmentation_fault" title="Segmentation fault">Segmentation fault</a></li>

<li><a href="Virtual_memory" title="Virtual memory">Virtual memory</a></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="Non-volatile_memory" title="Non-volatile memory">Storage</a> access,<br><a href="File_system" title="File system">file systems</a></th><td class="navbox-list-with-group navbox-list navbox-even hlist" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><a href="Booting#BOOT-LOADER" title="Booting">Boot loader</a></li>

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

<li><a href="Device_file" title="Device file">Device file</a></li>

<li><a href="File_attribute" title="File attribute">File attribute</a></li>

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

<li><a href="Journaling_file_system" title="Journaling file system">Journal</a></li>

<li><a href="Disk_partitioning" title="Disk partitioning">Partition</a></li>

<li><a href="Virtual_file_system" title="Virtual file system">Virtual file system</a></li>

<li><a href="Virtual_tape_library" title="Virtual tape library">Virtual tape library</a></li></ul>

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

<li><a href="Computer_network" title="Computer network">Computer network</a></li>

<li><a href="Shell_(computing)" title="Shell (computing)">Shell</a>

<li><a href="User_interface" title="User interface">User interface</a></li></ul></li>

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

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