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<title>Hazard (computer architecture)</title>

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<span id="openzim-page-title" class="mw-page-title-main"><span class="mw-page-title-main">Hazard (computer architecture)</span></span>

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<p>In the domain of <a href="Central_processing_unit" title="Central processing unit">central processing unit</a> (CPU) <a href="CPU_design" class="mw-redirect" title="CPU design">design</a>, <b>hazards</b> are problems with the <a href="Instruction_pipeline" class="mw-redirect" title="Instruction pipeline">instruction pipeline</a> in CPU <a href="Microarchitecture" title="Microarchitecture">microarchitectures</a> when the next instruction cannot execute in the following clock cycle,<sup id="cite_ref-FOOTNOTEPattersonHennessy2009335_1-0" class="reference"><a href="#cite_note-FOOTNOTEPattersonHennessy2009335-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup> and can potentially lead to incorrect computation results. Three common types of hazards are data hazards, structural hazards, and control hazards (branching hazards).<sup id="cite_ref-FOOTNOTEPattersonHennessy2009335–343_2-0" class="reference"><a href="#cite_note-FOOTNOTEPattersonHennessy2009335–343-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup>

</p><p>There are several methods used to deal with hazards, including <a href="Pipeline_stall" title="Pipeline stall">pipeline stalls</a>/pipeline bubbling, <a href="#Operand_forwarding">operand forwarding</a>, and in the case of <a href="Out-of-order_execution" title="Out-of-order execution">out-of-order execution</a>, the <a href="Scoreboarding" title="Scoreboarding">scoreboarding</a> method and the <a href="Tomasulo_algorithm" class="mw-redirect" title="Tomasulo algorithm">Tomasulo algorithm</a>.

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

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</style><div role="note" class="hatnote navigation-not-searchable">Further information: <a href="Instruction_pipelining" title="Instruction pipelining">Instruction pipelining</a></div>

<p><a href="Instruction_(computer_science)" class="mw-redirect" title="Instruction (computer science)">Instructions</a> in a pipelined processor are performed in several stages, so that at any given time several instructions are being processed in the various stages of the pipeline, such as fetch and execute. There are many different instruction pipeline <a href="Microarchitecture" title="Microarchitecture">microarchitectures</a>, and instructions may be <a href="Out-of-order_execution" title="Out-of-order execution">executed out-of-order</a>. A hazard occurs when two or more of these simultaneous (possibly out of order) instructions conflict.

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

<div class="mw-heading mw-heading3"><h3 id="Structural_hazards">Structural hazards</h3></div>

<p>A structural hazard occurs when two (or more) instructions that are already in pipeline need the same resource. The result is that instruction must be executed in series rather than parallel for a portion of pipeline. Structural hazards are sometimes referred to as resource hazards.

</p><p>Example:

A situation in which multiple instructions are ready to enter the execute instruction phase and there is a single ALU (Arithmetic Logic Unit). One solution to such resource hazard is to increase available resources, such as having multiple ports into main memory and multiple ALU (Arithmetic Logic Unit) units.

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<div class="mw-heading mw-heading3"><h3 id="Control_hazards_(branch_hazards_or_instruction_hazards)">Control hazards (branch hazards or instruction hazards)</h3></div>

<p>Control hazard occurs when the pipeline makes wrong decisions on branch prediction and therefore brings instructions into the pipeline that must subsequently be discarded. The term branch hazard also refers to a control hazard.

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<div class="mw-heading mw-heading2"><h2 id="Pipeline_bubbling">Pipeline bubbling</h2></div>

<div role="note" class="hatnote navigation-not-searchable">Main article: <a href="Bubble_(computing)" class="mw-redirect" title="Bubble (computing)">Bubble (computing)</a></div>

<p><i>Bubbling the pipeline</i>, also termed a <i>pipeline break</i> or <i>pipeline stall</i>, is a method to preclude data, structural, and branch hazards. As instructions are fetched, control logic determines whether a hazard could/will occur. If this is true, then the control logic inserts <style data-mw-deduplicate="TemplateStyles:r886049734">

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</style><span class="monospaced">no operation</span>s (<span class="monospaced"><a href="NOP_(code)" title="NOP (code)">NOP</a></span>s) into the pipeline. Thus, before the next instruction (which would cause the hazard) executes, the prior one will have had sufficient time to finish and prevent the hazard. If the number of <span class="monospaced">NOP</span>s equals the number of stages in the pipeline, the processor has been cleared of all instructions and can proceed free from hazards. All forms of stalling introduce a delay before the processor can resume execution.

</p><p><i>Flushing the pipeline</i> occurs when a branch instruction jumps to a new memory location, invalidating all prior stages in the pipeline. These prior stages are cleared, allowing the pipeline to continue at the new instruction indicated by the branch.<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><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>

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<div class="mw-heading mw-heading3"><h3 id="Data_hazards">Data hazards</h3></div>

<p>There are several main solutions and algorithms used to resolve data hazards:

</p>

<ul><li>insert a <i>pipeline bubble</i> whenever a read after write (RAW) dependency is encountered, guaranteed to increase latency, or</li>

<li>use <a href="Out-of-order_execution" title="Out-of-order execution">out-of-order execution</a> to potentially prevent the need for pipeline bubbles</li>

<li>use <i><a href="Operand_forwarding" title="Operand forwarding">operand forwarding</a></i> to use data from later stages in the pipeline</li></ul>

<p>In the case of <a href="Out-of-order_execution" title="Out-of-order execution">out-of-order execution</a>, the algorithm used can be:

</p>

<ul><li><a href="Scoreboarding" title="Scoreboarding">scoreboarding</a>, in which case a <i>pipeline bubble</i> is needed only when there is no functional unit available</li>

<li>the <a href="Tomasulo_algorithm" class="mw-redirect" title="Tomasulo algorithm">Tomasulo algorithm</a>, which uses <a href="Register_renaming" title="Register renaming">register renaming</a>, allowing continual issuing of instructions</li></ul>

<p>The task of removing data dependencies can be delegated to the compiler, which can fill in an appropriate number of <span class="monospaced">NOP</span> instructions between dependent instructions to ensure correct operation, or re-order instructions where possible.

</p>

<div class="mw-heading mw-heading4"><h4 id="Operand_forwarding">Operand forwarding</h4></div>

<div role="note" class="hatnote navigation-not-searchable">Main article: <a href="Operand_forwarding" title="Operand forwarding">Operand forwarding</a></div>

<div class="mw-heading mw-heading4"><h4 id="Examples">Examples</h4></div>

<dl><dd><i>In the following examples, computed values are in <b>bold</b>, while Register numbers are not.</i></dd></dl>

<p>For example, to write the value 3 to register 1, (which already contains a 6), and then add 7 to register 1 and store the result in register 2, i.e.:

</p>

i1: R1 = <b>3</b>

i2: R2 = R1 + <b>7</b> = <b>10</b>

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<p>Following execution, register 2 should contain the value <b>10</b>. However, if i1 (write <b>3</b> to register 1) does not fully exit the pipeline before i2 starts executing, it means that R1 does not contain the value <b>3</b> when i2 performs its addition. In such an event, i2 adds <b>7</b> to the old value of register 1 (<b>6</b>), and so register 2 contains <b>13</b> instead, i.e.:

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i2: R2 = R1 + <b>7</b> = <b>13</b>

i1: R1 = <b>3</b>

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<p>This error occurs because i2 reads Register 1 before i1 has committed/stored the result of its write operation to Register 1. So when i2 is reading the contents of Register 1, register 1 still contains <b>6</b>, <i>not</i> <b>3</b>.

</p><p>Forwarding (described below) helps correct such errors by depending on the fact that the output of i1 (which is <b>3</b>) can be used by subsequent instructions <i>before</i> the value <b>3</b> is committed to/stored in Register 1.

</p><p>Forwarding applied to the example means that <i>there is no wait to commit/store the output of i1 in Register 1 (in this example, the output is <b>3</b>) before making that output available to the subsequent instruction (in this case, i2).</i> The effect is that i2 uses the correct (the more recent) value of Register 1: the commit/store was made immediately and not pipelined.

</p><p>With forwarding enabled, the <i>Instruction Decode/Execution</i> (ID/EX) stage of the pipeline now has two inputs: the value read from the register specified (in this example, the value <b>6</b> from Register 1), and the new value of Register 1 (in this example, this value is <b>3</b>) which is sent from the next stage <i>Instruction Execute/Memory Access</i> (EX/MEM). Added control logic is used to determine which input to use.

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<div class="mw-heading mw-heading3"><h3 id="Control_hazards_(branch_hazards)">Control hazards (branch hazards)</h3></div>

<p>To avoid control hazards microarchitectures can:

</p>

<ul><li>insert a <i>pipeline bubble</i> (discussed above), guaranteed to increase <a href="Latency_(engineering)" title="Latency (engineering)">latency</a>, or</li>

<li>use <a href="Branch_prediction" class="mw-redirect" title="Branch prediction">branch prediction</a> and essentially make educated guesses about which instructions to insert, in which case a <i>pipeline bubble</i> will only be needed in the case of an incorrect prediction</li></ul>

<p>In the event that a branch causes a pipeline bubble after incorrect instructions have entered the pipeline, care must be taken to prevent any of the wrongly-loaded instructions from having any effect on the processor state excluding energy wasted processing them before they were discovered to be loaded incorrectly.

</p>

<div class="mw-heading mw-heading3"><h3 id="Other_techniques">Other techniques</h3></div>

<p>Memory latency is another factor that designers must attend to, because the delay could reduce performance. Different types of memory have different accessing time to the memory. Thus, by choosing a suitable type of memory, designers can improve the performance of the pipelined data path.<sup id="cite_ref-5" class="reference"><a href="#cite_note-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup>

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<ul><li><a href="Feed_forward_(control)" title="Feed forward (control)">Feed forward (control)</a></li>

<li><a href="Register_renaming" title="Register renaming">Register renaming</a></li>

<li><a href="Data_dependency" title="Data dependency">Data dependency</a></li>

<li><a href="Control_dependency" title="Control dependency">Control dependency</a></li>

<li><a href="Hazard_(logic)" title="Hazard (logic)">Hazard (logic)</a></li>

<li><a href="Hazard_pointer" title="Hazard pointer">Hazard pointer</a></li>

<li><a href="Classic_RISC_pipeline#Hazards" title="Classic RISC pipeline">Classic RISC pipeline § Hazards</a></li>

<li><a href="Speculative_execution" title="Speculative execution">Speculative execution</a></li>

<li><a href="Branch_delay_slot" class="mw-redirect" title="Branch delay slot">Branch delay slot</a></li>

<li><a href="Branch_predication" class="mw-redirect" title="Branch predication">Branch predication</a></li>

<li><a href="Branch_predictor" title="Branch predictor">Branch predictor</a></li>

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

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

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<li id="cite_note-FOOTNOTEPattersonHennessy2009335-1"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEPattersonHennessy2009335_1-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFPattersonHennessy2009">Patterson & Hennessy 2009</a>, p. 335.</span>

</li>

<li id="cite_note-FOOTNOTEPattersonHennessy2009335–343-2"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEPattersonHennessy2009335–343_2-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFPattersonHennessy2009">Patterson & Hennessy 2009</a>, pp. 335–343.</span>

</li>

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</style><cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://www.cs.iastate.edu/~prabhu/Tutorial/PIPELINE/branchPred.html">"Branch Prediction Schemes"</a>. <i>cs.iastate.edu</i>. 2001-04-06<span class="reference-accessdate">. Retrieved <span class="nowrap">2014-07-19</span></span>.</cite></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"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://classes.soe.ucsc.edu/cmpe110/Winter04/pipelining.txt">"Data and Control Hazards"</a>. <i>classes.soe.ucsc.edu</i>. 2004-02-23<span class="reference-accessdate">. Retrieved <span class="nowrap">2014-07-19</span></span>.</cite></span>

</li>

<li id="cite_note-5"><span class="mw-cite-backlink"><b><a href="#cite_ref-5">^</a></b></span> <span class="reference-text"><cite id="CITEREFCheng2012" class="citation journal cs1">Cheng, Ching-Hwa (2012-12-27). <a rel="nofollow" class="external text" href="https://doi.org/10.1155%2F2013%2F425105">"Design Example of Useful Memory Latency for Developing a Hazard Preventive Pipeline High-Performance Embedded-Microprocessor"</a>. <i>VLSI Design</i>. <b>2013</b>: <span class="nowrap">1–</span>10. <a href="Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<span class="id-lock-free" title="Freely accessible"><a rel="nofollow" class="external text" href="https://doi.org/10.1155%2F2013%2F425105">10.1155/2013/425105</a></span>.</cite></span>

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<div class="mw-heading mw-heading3"><h3 id="General">General</h3></div>

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<ul><li><cite id="CITEREFPattersonHennessy2009" class="citation book cs1"><a href="David_Patterson_(scientist)" class="mw-redirect" title="David Patterson (scientist)">Patterson, David</a>; <a href="John_L._Hennessy" title="John L. Hennessy">Hennessy, John</a> (2009). <i>Computer Organization and Design</i> (4th ed.). <a href="Morgan_Kaufmann" class="mw-redirect" title="Morgan Kaufmann">Morgan Kaufmann</a>. <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <bdi>978-0-12-374493-7</bdi>.</cite></li>

<li><cite id="CITEREFPattersonHennessy2011" class="citation book cs1">Patterson, David; Hennessy, John (2011). <i>Computer Architecture: A Quantitative Approach</i> (5th ed.). <a href="Morgan_Kaufmann" class="mw-redirect" title="Morgan Kaufmann">Morgan Kaufmann</a>. <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <bdi>978-0-12-383872-8</bdi>.</cite></li>

<li><cite id="CITEREFShenLipasti2013" class="citation book cs1">Shen, John P.; Lipasti, Mikko H. (2013) [2004]. <a rel="nofollow" class="external text" href="https://books.google.com/books?id=ffQqAAAAQBAJ&pg=PA73">"2.2.3.2 Identication of Pipeline Hazards"</a>. <i>Modern Processor Design: Fundamentals of Superscalar Processors</i>. Waveland Press. pp. <span class="nowrap">73–</span>78. <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <bdi>9781478610762</bdi>.</cite></li></ul>

</div>

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

<ul><li><cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://users.ece.cmu.edu/~jhoe/distribution/2010/date10.pdf">"Automatic Pipelining from Transactional Datapath Specifications"</a> <span class="cs1-format">(PDF)</span><span class="reference-accessdate">. Retrieved <span class="nowrap">23 July</span> 2014</span>.</cite></li>

<li><cite id="CITEREFTulsen2005" class="citation web cs1">Tulsen, Dean (18 January 2005). <a rel="nofollow" class="external text" href="http://cseweb.ucsd.edu/classes/wi05/cse240a/pipe2.pdf">"Pipeline hazards"</a> <span class="cs1-format">(PDF)</span>.</cite></li></ul>

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</style><div id="Processor_technologies439" style="font-size:114%;margin:0 4em"><a href="Processor_(computing)" title="Processor (computing)">Processor technologies</a></div></th></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="Model_of_computation" title="Model of computation">Models</a></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="Abstract_machine" title="Abstract machine">Abstract machine</a></li>

<li><a href="Stored-program_computer" title="Stored-program computer">Stored-program computer</a></li>

<li><a href="Finite-state_machine" title="Finite-state machine">Finite-state machine</a>

<ul><li><a href="Finite-state_machine_with_datapath" class="mw-redirect" title="Finite-state machine with datapath">with datapath</a></li>

<li><a href="Hierarchical_state_machine" class="mw-redirect" title="Hierarchical state machine">Hierarchical</a></li>

<li><a href="Deterministic_finite_automaton" title="Deterministic finite automaton">Deterministic finite automaton</a></li>

<li><a href="Queue_automaton" title="Queue automaton">Queue automaton</a></li>

<li><a href="Cellular_automaton" title="Cellular automaton">Cellular automaton</a></li>

<li><a href="Quantum_cellular_automaton" title="Quantum cellular automaton">Quantum cellular automaton</a></li></ul></li>

<li><a href="Turing_machine" title="Turing machine">Turing machine</a>

<ul><li><a href="Alternating_Turing_machine" title="Alternating Turing machine">Alternating Turing machine</a></li>

<li><a href="Universal_Turing_machine" title="Universal Turing machine">Universal</a></li>

<li><a href="Post%E2%80%93Turing_machine" title="Post–Turing machine">Post–Turing</a></li>

<li><a href="Quantum_Turing_machine" title="Quantum Turing machine">Quantum</a></li>

<li><a href="Nondeterministic_Turing_machine" title="Nondeterministic Turing machine">Nondeterministic Turing machine</a></li>

<li><a href="Probabilistic_Turing_machine" title="Probabilistic Turing machine">Probabilistic Turing machine</a></li>

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

<li><a href="Zeno_machine" title="Zeno machine">Zeno machine</a></li></ul></li>

<li><a href="History_of_general-purpose_CPUs#Belt_machine_architecture" title="History of general-purpose CPUs">Belt machine</a></li>

<li><a href="Stack_machine" title="Stack machine">Stack machine</a></li>

<li><a href="Register_machine" title="Register machine">Register machines</a>

<ul><li><a href="Counter_machine" title="Counter machine">Counter</a></li>

<li><a href="Pointer_machine" title="Pointer machine">Pointer</a></li>

<li><a href="Random-access_machine" title="Random-access machine">Random-access</a></li>

<li><a href="Random-access_stored-program_machine" title="Random-access stored-program machine">Random-access stored program</a></li></ul></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="Computer_architecture" title="Computer architecture">Architecture</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="Microarchitecture" title="Microarchitecture">Microarchitecture</a></li>

<li><a href="Von_Neumann_architecture" title="Von Neumann architecture">Von Neumann</a></li>

<li><a href="Harvard_architecture" title="Harvard architecture">Harvard</a>

<ul><li><a href="Modified_Harvard_architecture" title="Modified Harvard architecture">modified</a></li></ul></li>

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

<li><a href="Transport_triggered_architecture" title="Transport triggered architecture">Transport-triggered</a></li>

<li><a href="Cellular_architecture" title="Cellular architecture">Cellular</a></li>

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

<li><a href="Computer_data_storage" title="Computer data storage">Memory access</a>

<li><a href="Load%E2%80%93store_architecture" title="Load–store architecture">Load–store</a></li>

<li><a href="Register%E2%80%93memory_architecture" title="Register–memory architecture">Register/memory</a></li></ul></li>

<li><a href="Cache_hierarchy" title="Cache hierarchy">Cache hierarchy</a></li>

<li><a href="Memory_hierarchy" title="Memory hierarchy">Memory hierarchy</a>

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

<li><a href="Secondary_storage" class="mw-redirect" title="Secondary storage">Secondary storage</a></li></ul></li>

<li><a href="Heterogeneous_System_Architecture" title="Heterogeneous System Architecture">Heterogeneous</a></li>

<li><a href="Fabric_computing" title="Fabric computing">Fabric</a></li>

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

<li><a href="Cognitive_computing" title="Cognitive computing">Cognitive</a></li>

<li><a href="Neuromorphic_engineering" class="mw-redirect" title="Neuromorphic engineering">Neuromorphic</a></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="Instruction_set_architecture" title="Instruction set architecture">Instruction set<br>architectures</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:1%">Types</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="Orthogonal_instruction_set" title="Orthogonal instruction set">Orthogonal instruction set</a></li>

<li><a href="Application-specific_instruction_set_processor" title="Application-specific instruction set processor">Application-specific</a></li>

<ul><li><a href="TRIPS_architecture" title="TRIPS architecture">TRIPS</a></li></ul></li>

<li><a href="VISC_architecture" title="VISC architecture">VISC architecture</a></li>

<li><a href="Quantum_computing" title="Quantum computing">Quantum computing</a></li>

<li><a href="Comparison_of_instruction_set_architectures" title="Comparison of instruction set architectures">Comparison</a>

<ul><li><a href="Addressing_mode" title="Addressing mode">Addressing modes</a></li></ul></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Instruction<br>sets</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="Motorola_68000_series" title="Motorola 68000 series">Motorola 68000 series</a></li>

<li><a href="Stanford_MIPS" title="Stanford MIPS">Stanford MIPS</a></li>

<li>Power

<ul><li><a href="IBM_POWER_architecture" title="IBM POWER architecture">POWER</a></li>

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

<li><a href="Power_ISA" title="Power ISA">Power ISA</a></li></ul></li>

<li><a href="Clipper_architecture" title="Clipper architecture">Clipper architecture</a></li>

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

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

<li><a href="DEC_Alpha" title="DEC Alpha">DEC Alpha</a></li>

<li><a href="ETRAX_CRIS" title="ETRAX CRIS">ETRAX CRIS</a></li>

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

<li><a href="IA-64" title="IA-64">Itanium</a></li>

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

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

<li>System/3x0

<li><a href="Z/Architecture" title="Z/Architecture">z/Architecture</a></li></ul></li>

<li>Tilera ISA</li>

<li><a href="VISC_architecture" title="VISC architecture">VISC architecture</a></li>

<li><a href="Adapteva" class="mw-redirect" title="Adapteva">Epiphany architecture</a></li>

<li><a href="Comparison_of_instruction_set_architectures" title="Comparison of instruction set architectures">Others</a></li></ul>

</div></td></tr></tbody></table><div></div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="Instruction_cycle" title="Instruction cycle">Execution</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:1%"><a href="Instruction_pipelining" title="Instruction pipelining">Instruction pipelining</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="Pipeline_stall" title="Pipeline stall">Pipeline stall</a></li>

<li><a href="Operand_forwarding" title="Operand forwarding">Operand forwarding</a></li>

<li><a href="Classic_RISC_pipeline" title="Classic RISC pipeline">Classic RISC pipeline</a></li></ul>

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

<li><a href="Structural_hazard" class="mw-redirect" title="Structural hazard">Structural</a></li>

<li><a href="Control_hazard" class="mw-redirect" title="Control hazard">Control</a></li>

<li><a href="False_sharing" title="False sharing">False sharing</a></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="Out-of-order_execution" title="Out-of-order execution">Out-of-order</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="Scoreboarding" title="Scoreboarding">Scoreboarding</a></li>

<li><a href="Tomasulo's_algorithm" title="Tomasulo's algorithm">Tomasulo's algorithm</a>

<ul><li><a href="Reservation_station" title="Reservation station">Reservation station</a></li>

<li><a href="Re-order_buffer" title="Re-order buffer">Re-order buffer</a></li></ul></li>

<li><a href="Register_renaming" title="Register renaming">Register renaming</a></li>

<li><a href="Wide-issue" title="Wide-issue">Wide-issue</a></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="Speculative_execution" title="Speculative execution">Speculative</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="Branch_predictor" title="Branch predictor">Branch prediction</a></li>

<li><a href="Memory_dependence_prediction" title="Memory dependence prediction">Memory dependence prediction</a></li></ul>

</div></td></tr></tbody></table><div></div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="Parallel_computing" title="Parallel computing">Parallelism</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:1%">Level</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="Bit-serial_architecture" title="Bit-serial architecture">Bit-serial</a></li>

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

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

<ul><li><a href="Scalar_processor" title="Scalar processor">Scalar</a></li>

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

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

<li><a href="Process_(computing)" title="Process (computing)">Process</a></li></ul></li>

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

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

<li><a href="Distributed_architecture" class="mw-redirect" title="Distributed architecture">Distributed</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-even" 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>

<ul><li><a href="Hyper-threading" title="Hyper-threading">Hyperthreading</a></li>

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

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

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

<li><a href="Cooperative_multitasking" title="Cooperative multitasking">Cooperative</a></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="Flynn's_taxonomy" title="Flynn's taxonomy">Flynn's taxonomy</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="Single_instruction%2C_multiple_threads" title="Single instruction, multiple threads">Array processing (SIMT)</a></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>

</div></td></tr></tbody></table><div></div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="Computer_performance" title="Computer performance">Processor<br>performance</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="Transistor_count" title="Transistor count">Transistor count</a></li>

<li><a href="Instructions_per_cycle" title="Instructions per cycle">Instructions per cycle</a> (IPC)

<ul><li><a href="Cycles_per_instruction" title="Cycles per instruction">Cycles per instruction</a> (CPI)</li></ul></li>

<li><a href="Instructions_per_second" title="Instructions per second">Instructions per second</a> (IPS)</li>

<li><a href="FLOPS" class="mw-redirect" title="FLOPS">Floating-point operations per second</a> (FLOPS)</li>

<li><a href="Transactions_per_second" title="Transactions per second">Transactions per second</a> (TPS)</li>

<li><a href="SUPS" title="SUPS">Synaptic updates per second</a> (SUPS)</li>

<li><a href="Performance_per_watt" title="Performance per watt">Performance per watt</a> (PPW)</li>

<li><a href="Cache_performance_measurement_and_metric" title="Cache performance measurement and metric">Cache performance metrics</a></li>

<li><a href="Computer_performance_by_orders_of_magnitude" title="Computer performance by orders of magnitude">Computer performance by orders of magnitude</a></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="Processor_(computing)" title="Processor (computing)">Types</a></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="Central_processing_unit" title="Central processing unit">Central processing unit</a> (CPU)</li>

<li><a href="Graphics_processing_unit" title="Graphics processing unit">Graphics processing unit</a> (GPU)

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

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

<li><a href="Barrel_processor" title="Barrel processor">Barrel</a></li>

<li><a href="Stream_processing" title="Stream processing">Stream</a></li>

<li><a href="Tile_processor" title="Tile processor">Tile processor</a></li>

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

<li><a href="Multi-chip_module" title="Multi-chip module">Multi-chip module</a> (MCM)</li>

<li><a href="System_in_a_package" title="System in a package">System in a package</a> (SiP)</li>

<li><a href="Package_on_a_package" title="Package on a package">Package on a package</a> (PoP)</li></ul>

</div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:1%">By application</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="Embedded_system" title="Embedded system">Embedded system</a></li>

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

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

<li><a href="Mobile_processor" title="Mobile processor">Mobile</a></li>

<li><a href="Ultra-low-voltage_processor" title="Ultra-low-voltage processor">Ultra-low-voltage</a></li>

<li><a href="Soft_microprocessor" title="Soft microprocessor">Soft microprocessor</a></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Systems<br>on chip</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="System_on_a_chip" title="System on a chip">System on a chip</a> (SoC)</li>

<li><a href="Multiprocessor_system_on_a_chip" class="mw-redirect" title="Multiprocessor system on a chip">Multiprocessor</a> (MPSoC)</li>

<li><a href="Cypress_PSoC" title="Cypress PSoC">Cypress PSoC</a></li>

<li><a href="Network_on_a_chip" title="Network on a chip">Network on a chip</a> (NoC)</li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="Hardware_acceleration" title="Hardware acceleration">Hardware<br>accelerators</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="Coprocessor" title="Coprocessor">Coprocessor</a></li>

<li><a href="AI_accelerator" class="mw-redirect" title="AI accelerator">AI accelerator</a></li>

<li><a href="Graphics_processing_unit" title="Graphics processing unit">Graphics processing unit</a> (GPU)</li>

<li><a href="Image_processor" title="Image processor">Image processor</a></li>

<li><a href="Vision_processing_unit" title="Vision processing unit">Vision processing unit</a> (VPU)</li>

<li><a href="Physics_processing_unit" title="Physics processing unit">Physics processing unit</a> (PPU)</li>

<li><a href="Digital_signal_processor" title="Digital signal processor">Digital signal processor</a> (DSP)</li>

<li><a href="Tensor_Processing_Unit" title="Tensor Processing Unit">Tensor Processing Unit</a> (TPU)</li>

<li><a href="Secure_cryptoprocessor" title="Secure cryptoprocessor">Secure cryptoprocessor</a></li>

<li><a href="Network_processor" title="Network processor">Network processor</a></li>

<li><a href="Baseband_processor" title="Baseband processor">Baseband processor</a></li></ul>

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

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="Word_(computer_architecture)" title="Word (computer architecture)">Word size</a></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="Bit_slicing" title="Bit slicing">bit slicing</a></li>

<li><a href="Word_(computer_architecture)#Table_of_word_sizes" title="Word (computer architecture)">others</a>

<ul><li><a href="Word_(computer_architecture)#Variable-word_architectures" title="Word (computer architecture)">variable</a></li></ul></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Core count</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="Single-core" title="Single-core">Single-core</a></li>

<li><a href="Multi-core_processor" title="Multi-core processor">Multi-core</a></li>

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

<li><a href="Heterogeneous_computing" title="Heterogeneous computing">Heterogeneous architecture</a></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Components</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="Cache_(computing)" title="Cache (computing)">Cache</a>

<ul><li><a href="CPU_cache" title="CPU cache">CPU cache</a></li>

<li><a href="Scratchpad_memory" title="Scratchpad memory">Scratchpad memory</a></li>

<li><a href="Data_cache" class="mw-redirect" title="Data cache">Data cache</a></li>

<li><a href="Instruction_cache" class="mw-redirect" title="Instruction cache">Instruction cache</a></li>

<li><a href="Cache_replacement_policies" title="Cache replacement policies">replacement policies</a></li>

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

<li><a href="Clock_rate" title="Clock rate">Clock rate</a></li>

<li><a href="Clock_signal" title="Clock signal">Clock signal</a></li>

</div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:1%"><a href="Execution_unit" title="Execution unit">Functional<br>units</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="Arithmetic_logic_unit" title="Arithmetic logic unit">Arithmetic logic unit</a> (ALU)</li>

<li><a href="Address_generation_unit" title="Address generation unit">Address generation unit</a> (AGU)</li>

<li><a href="Floating-point_unit" title="Floating-point unit">Floating-point unit</a> (FPU)</li>

<li><a href="Memory_management_unit" title="Memory management unit">Memory management unit</a> (MMU)

<ul><li><a href="Load%E2%80%93store_unit" title="Load–store unit">Load–store unit</a></li>

<li><a href="Translation_lookaside_buffer" title="Translation lookaside buffer">Translation lookaside buffer</a> (TLB)</li></ul></li>

<li><a href="Branch_predictor" title="Branch predictor">Branch predictor</a></li>

<li><a href="Branch_target_predictor" title="Branch target predictor">Branch target predictor</a></li>

<li><a href="Memory_controller" title="Memory controller">Integrated memory controller</a> (IMC)

<ul><li><a href="Memory_management_unit" title="Memory management unit">Memory management unit</a></li></ul></li>

<li><a href="Instruction_decoder" class="mw-redirect" title="Instruction decoder">Instruction decoder</a></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="Logic_gate" title="Logic gate">Logic</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="Combinational_logic" title="Combinational logic">Combinational</a></li>

<li><a href="Sequential_logic" title="Sequential logic">Sequential</a></li>

<li><a href="Logic_gate" title="Logic gate">Logic gate</a>

<ul><li><a href="Quantum_logic_gate" title="Quantum logic gate">Quantum</a></li>

<li><a href="Gate_array" title="Gate array">Array</a></li></ul></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="Hardware_register" title="Hardware register">Registers</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="Processor_register" title="Processor register">Processor register</a></li>

<li><a href="Status_register" title="Status register">Status register</a></li>

<li><a href="Stack_register" title="Stack register">Stack register</a></li>

<li><a href="Register_file" title="Register file">Register file</a></li>

<li><a href="Memory_buffer_register" title="Memory buffer register">Memory buffer</a></li>

<li><a href="Memory_address_register" title="Memory address register">Memory address register</a></li>

<li><a href="Program_counter" title="Program counter">Program counter</a></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="Control_unit" title="Control unit">Control unit</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="Hardwired_control_unit" class="mw-redirect" title="Hardwired control unit">Hardwired control unit</a></li>

<li><a href="Instruction_unit" title="Instruction unit">Instruction unit</a></li>

<li><a href="Data_buffer" title="Data buffer">Data buffer</a></li>

<li><a href="Write_buffer" title="Write buffer">Write buffer</a></li>

<li><a href="Microcode" title="Microcode">Microcode</a> <a href="ROM_image" title="ROM image">ROM</a></li>

<li><a href="Counter_(digital)" title="Counter (digital)">Counter</a></li></ul>

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

<li><a href="Demultiplexer" class="mw-redirect" title="Demultiplexer">Demultiplexer</a></li>

<li><a href="Adder_(electronics)" title="Adder (electronics)">Adder</a></li>

<li><a href="Binary_multiplier" title="Binary multiplier">Multiplier</a>

<li><a href="Binary_decoder" title="Binary decoder">Binary decoder</a>

<ul><li><a href="Address_decoder" title="Address decoder">Address decoder</a></li>

<li><a href="Sum-addressed_decoder" title="Sum-addressed decoder">Sum-addressed decoder</a></li></ul></li>

<li><a href="Barrel_shifter" title="Barrel shifter">Barrel shifter</a></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="Electronic_circuit" title="Electronic circuit">Circuitry</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="Integrated_circuit" title="Integrated circuit">Integrated circuit</a>

<li><a href="Mixed-signal_integrated_circuit" title="Mixed-signal integrated circuit">Mixed-signal</a></li>

<li><a href="Power_management_integrated_circuit" title="Power management integrated circuit">Power management</a></li></ul></li>

<li><a href="Boolean_circuit" title="Boolean circuit">Boolean</a></li>

<li><a href="Circuit_(computer_science)" title="Circuit (computer science)">Digital</a></li>

<li><a href="Analogue_electronics" title="Analogue electronics">Analog</a></li>

<li><a href="Quantum_circuit" title="Quantum circuit">Quantum</a></li>

<li><a href="Switch#Electronic_switches" title="Switch">Switch</a></li></ul>

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

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

<li><a href="Dynamic_frequency_scaling" title="Dynamic frequency scaling">Dynamic frequency scaling</a></li>

<li><a href="Dynamic_voltage_scaling" title="Dynamic voltage scaling">Dynamic voltage scaling</a></li>

<li><a href="Clock_gating" title="Clock gating">Clock gating</a></li>

<li><a href="Performance_per_watt" title="Performance per watt">Performance per watt</a> (PPW)</li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Related</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="History_of_general-purpose_CPUs" title="History of general-purpose CPUs">History of general-purpose CPUs</a></li>

<li><a href="Microprocessor_chronology" title="Microprocessor chronology">Microprocessor chronology</a></li>

<li><a href="Processor_design" title="Processor design">Processor design</a></li>

<li><a href="Digital_electronics" title="Digital electronics">Digital electronics</a></li>

<li><a href="Hardware_security_module" title="Hardware security module">Hardware security module</a></li>

<li><a href="Semiconductor_device_fabrication" title="Semiconductor device fabrication">Semiconductor device fabrication</a></li>

<li><a href="Tick%E2%80%93tock_model" title="Tick–tock model">Tick–tock model</a></li>

<li><a href="Pin_grid_array" title="Pin grid array">Pin grid array</a></li>

<li><a href="Chip_carrier" title="Chip carrier">Chip carrier</a></li></ul>

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

This article is issued from <a class="external text" title="Last edited on 2025-07-07" href="https://en.wikipedia.org/wiki/?title=Hazard_(computer_architecture)&oldid=1299318182">Wikipedia</a>. The text is available under <a class="external text" href="https://creativecommons.org/licenses/by-sa/4.0/deed.en">Creative Commons Attribution-Share Alike 4.0</a> unless otherwise noted. Additional terms may apply for the media files.

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