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id="toc-Effect_of_audible_noise_and_vibration_control" class="vector-toc-list-item vector-toc-level-3"> <a class="vector-toc-link" href="#Effect_of_audible_noise_and_vibration_control"> <div class="vector-toc-text"> <span class="vector-toc-numb">1.2.2</span> <span>Effect of audible noise and vibration control</span> </div> </a> <ul id="toc-Effect_of_audible_noise_and_vibration_control-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Rotational_latency" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Rotational_latency"> <div class="vector-toc-text"> <span class="vector-toc-numb">1.3</span> <span>Rotational latency</span> </div> </a> <ul id="toc-Rotational_latency-sublist" class="vector-toc-list"> <li id="toc-Effect_of_reduced_power_consumption" class="vector-toc-list-item vector-toc-level-3"> <a class="vector-toc-link" href="#Effect_of_reduced_power_consumption"> <div class="vector-toc-text"> <span class="vector-toc-numb">1.3.1</span> <span>Effect of reduced power consumption</span> </div> </a> <ul id="toc-Effect_of_reduced_power_consumption-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Other" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Other"> <div class="vector-toc-text"> <span class="vector-toc-numb">1.4</span> <span>Other</span> </div> </a> <ul id="toc-Other-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Data_transfer_rate" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Data_transfer_rate"> <div class="vector-toc-text"> <span class="vector-toc-numb">2</span> <span>Data transfer rate</span> </div> </a> <button aria-controls="toc-Data_transfer_rate-sublist" class="cdx-button cdx-button--weight-quiet cdx-button--icon-only vector-toc-toggle"> <span class="vector-icon mw-ui-icon-wikimedia-expand"></span> <span>Toggle Data transfer rate subsection</span> </button> <ul id="toc-Data_transfer_rate-sublist" class="vector-toc-list"> <li id="toc-Effect_of_file_system" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Effect_of_file_system"> <div class="vector-toc-text"> <span class="vector-toc-numb">2.1</span> <span>Effect of file system</span> </div> </a> <ul id="toc-Effect_of_file_system-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Effect_of_areal_density" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Effect_of_areal_density"> <div class="vector-toc-text"> <span class="vector-toc-numb">2.2</span> <span>Effect of areal density</span> </div> </a> <ul id="toc-Effect_of_areal_density-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Interleave" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Interleave"> <div class="vector-toc-text"> <span class="vector-toc-numb">2.3</span> <span>Interleave</span> </div> </a> <ul id="toc-Interleave-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Power_consumption" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Power_consumption"> <div class="vector-toc-text"> <span class="vector-toc-numb">3</span> <span>Power consumption</span> </div> </a> <ul id="toc-Power_consumption-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Shock_resistance" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Shock_resistance"> <div class="vector-toc-text"> <span class="vector-toc-numb">4</span> <span>Shock resistance</span> </div> </a> <ul id="toc-Shock_resistance-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-SMR_drives" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#SMR_drives"> <div class="vector-toc-text"> <span class="vector-toc-numb">5</span> <span>SMR drives</span> </div> </a> <ul id="toc-SMR_drives-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Comparison_to_solid-state_drives" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Comparison_to_solid-state_drives"> <div class="vector-toc-text"> <span class="vector-toc-numb">6</span> <span>Comparison to solid-state drives</span> </div> </a> <ul id="toc-Comparison_to_solid-state_drives-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-See_also" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#See_also"> <div class="vector-toc-text"> <span class="vector-toc-numb">7</span> <span>See also</span> </div> </a> <ul id="toc-See_also-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-References" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#References"> <div class="vector-toc-text"> <span class="vector-toc-numb">8</span> <span>References</span> </div> </a> <ul id="toc-References-sublist" class="vector-toc-list"> </ul> </li> </ul> </div> </div> </nav> </div> </div> <div class="mw-content-container"> <main id="content" class="mw-body"> <header class="mw-body-header vector-page-titlebar"> <nav aria-label="Contents" class="vector-toc-landmark"> <div id="vector-page-titlebar-toc" class="vector-dropdown vector-page-titlebar-toc vector-button-flush-left" title="Table of Contents" > <input type="checkbox" id="vector-page-titlebar-toc-checkbox" role="button" aria-haspopup="true" data-event-name="ui.dropdown-vector-page-titlebar-toc" class="vector-dropdown-checkbox " aria-label="Toggle the table of contents" > <label id="vector-page-titlebar-toc-label" for="vector-page-titlebar-toc-checkbox" class="vector-dropdown-label cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet 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</div> </div> <div id="bodyContent" class="vector-body" aria-labelledby="firstHeading" data-mw-ve-target-container> <div class="vector-body-before-content"> <div class="mw-indicators"> </div> <div id="siteSub" class="noprint">From Wikipedia, the free encyclopedia</div> </div> <div id="contentSub"><div id="mw-content-subtitle"><span class="mw-redirectedfrom">(Redirected from <a href="/w/index.php?title=Seek_time&redirect=no" class="mw-redirect" title="Seek time">Seek time</a>)</span></div></div> <div id="mw-content-text" class="mw-body-content"><div class="mw-content-ltr mw-parser-output" lang="en" dir="ltr"><p> Higher performance in <a href="/wiki/Hard_disk_drive" title="Hard disk drive">hard disk drives</a> comes from devices which have better performance characteristics.<sup id="cite_ref-PCTechGuide_1-0" class="reference"><a href="#cite_note-PCTechGuide-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-RedHat_2-0" class="reference"><a href="#cite_note-RedHat-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup> These performance characteristics can be grouped into two categories: <a href="#Access_time">access time</a> and <a href="#Data_transfer_rate">data transfer time (or rate)</a>.<sup id="cite_ref-RefGuide-Access_3-0" class="reference"><a href="#cite_note-RefGuide-Access-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup> </p> <meta property="mw:PageProp/toc" /> <div class="mw-heading mw-heading2"><h2 id="Access_time">Access time</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Hard_disk_drive_performance_characteristics&action=edit&section=1" title="Edit section: Access time"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Hard_Disk_head_top.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/5/5b/Hard_Disk_head_top.jpg/220px-Hard_Disk_head_top.jpg" decoding="async" width="220" height="147" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/5/5b/Hard_Disk_head_top.jpg/330px-Hard_Disk_head_top.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/5/5b/Hard_Disk_head_top.jpg/440px-Hard_Disk_head_top.jpg 2x" data-file-width="2291" data-file-height="1526" /></a><figcaption>A hard disk head on an access arm resting on a hard disk platter</figcaption></figure> <p>The <i>access time</i> or <i>response time</i> of a rotating drive is a measure of the time it takes before the drive can actually <a href="/wiki/Data_transmission" class="mw-redirect" title="Data transmission">transfer data</a>. The factors that control this time on a rotating drive are mostly related to the mechanical nature of the rotating disks and moving <a href="/wiki/Disk_read-and-write_head" title="Disk read-and-write head">heads</a>. It is composed of a few independently measurable elements that are added together to get a single value when evaluating the performance of a storage device. The access time can vary significantly, so it is typically provided by manufacturers or measured in benchmarks as an average.<sup id="cite_ref-RefGuide-Access_3-1" class="reference"><a href="#cite_note-RefGuide-Access-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Symantec_4-0" class="reference"><a href="#cite_note-Symantec-4"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup> </p><p>The key components that are typically added together to obtain the access time are:<sup id="cite_ref-RedHat_2-1" class="reference"><a href="#cite_note-RedHat-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-HDD_Glossary_5-0" class="reference"><a href="#cite_note-HDD_Glossary-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup> </p> <ul><li><a href="#Seek_time">Seek time</a></li> <li><a href="#Rotational_latency">Rotational latency</a></li> <li><a href="#Command_processing_time">Command processing time</a></li> <li><a href="#Settle_time">Settle time</a></li></ul> <div class="mw-heading mw-heading3"><h3 id="Seek_time"><span class="anchor" id="SEEKTIME"></span>Seek time</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Hard_disk_drive_performance_characteristics&action=edit&section=2" title="Edit section: Seek time"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>With rotating drives, the <i>seek time</i> measures the time it takes the head assembly on the actuator arm to travel to the track of the disk where the data will be read or written.<sup id="cite_ref-HDD_Glossary_5-1" class="reference"><a href="#cite_note-HDD_Glossary-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup> The data on the media is stored in sectors which are arranged in parallel circular tracks (<a href="/wiki/Concentric" class="mw-redirect" title="Concentric">concentric</a> or <a href="/wiki/Spiral" title="Spiral">spiral</a> depending upon the <a href="/wiki/Disk_storage#CAV-CLV" title="Disk storage">device type</a>) and there is an actuator with an arm that suspends a head that can transfer data with that media. When the drive needs to read or write a certain sector it determines in which track the sector is located.<sup id="cite_ref-6" class="reference"><a href="#cite_note-6"><span class="cite-bracket">[</span>6<span class="cite-bracket">]</span></a></sup> It then uses the actuator to move the head to that particular track. If the initial location of the head was the desired track then the seek time would be zero. If the initial track was the outermost edge of the media and the desired track was at the innermost edge then the seek time would be the maximum for that drive.<sup id="cite_ref-RefGuide-Seek_7-0" class="reference"><a href="#cite_note-RefGuide-Seek-7"><span class="cite-bracket">[</span>7<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-RefGuide-Track_8-0" class="reference"><a href="#cite_note-RefGuide-Track-8"><span class="cite-bracket">[</span>8<span class="cite-bracket">]</span></a></sup> Seek times are not linear compared with the seek distance traveled because of factors of acceleration and deceleration of the actuator arm.<sup id="cite_ref-Intro_Disk_Modeling_9-0" class="reference"><a href="#cite_note-Intro_Disk_Modeling-9"><span class="cite-bracket">[</span>9<span class="cite-bracket">]</span></a></sup> </p><p>A rotating drive's <i>average seek time</i> is the average of all possible seek times which technically is the time to do all possible seeks divided by the number of all possible seeks, but in practice it is determined by statistical methods or simply approximated as the time of a seek over one-third of the number of tracks.<sup id="cite_ref-HDD_Glossary_5-2" class="reference"><a href="#cite_note-HDD_Glossary-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-RefGuide-Seek_7-1" class="reference"><a href="#cite_note-RefGuide-Seek-7"><span class="cite-bracket">[</span>7<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Auto6R-2_10-0" class="reference"><a href="#cite_note-Auto6R-2-10"><span class="cite-bracket">[</span>10<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Seek_times_&_characteristics"><span id="Seek_times_.26_characteristics"></span>Seek times & characteristics</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Hard_disk_drive_performance_characteristics&action=edit&section=3" title="Edit section: Seek times & characteristics"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The first HDD<sup id="cite_ref-Auto6R-3_11-0" class="reference"><a href="#cite_note-Auto6R-3-11"><span class="cite-bracket">[</span>11<span class="cite-bracket">]</span></a></sup> had an average seek time of about 600 ms.<sup id="cite_ref-IBM350_12-0" class="reference"><a href="#cite_note-IBM350-12"><span class="cite-bracket">[</span>12<span class="cite-bracket">]</span></a></sup> and by the middle 1970s, HDDs were available with seek times of about 25 ms.<sup id="cite_ref-Auto6R-4_13-0" class="reference"><a href="#cite_note-Auto6R-4-13"><span class="cite-bracket">[</span>13<span class="cite-bracket">]</span></a></sup> Some early PC drives used a <a href="/wiki/Stepper_motor" title="Stepper motor">stepper motor</a> to move the heads, and as a result had seek times as slow as 80–120 ms, but this was quickly improved by <a href="/wiki/Voice_coil" title="Voice coil">voice coil</a> type actuation in the 1980s, reducing seek times to around 20 ms. Seek time has continued to improve slowly over time. </p><p>The fastest high-end server drives of 2010 had a seek time around 4 <a href="/wiki/Millisecond" title="Millisecond">ms</a>.<sup id="cite_ref-14" class="reference"><a href="#cite_note-14"><span class="cite-bracket">[</span>14<span class="cite-bracket">]</span></a></sup> Some mobile devices have 15 ms drives, with the most common mobile drives at about 12 ms<sup id="cite_ref-WD-Scorpio_Blue-specs_15-0" class="reference"><a href="#cite_note-WD-Scorpio_Blue-specs-15"><span class="cite-bracket">[</span>15<span class="cite-bracket">]</span></a></sup> and the most common desktop drives typically being around 9 ms. </p><p>Two other less commonly referenced seek measurements are <i>track-to-track</i> and <i>full stroke</i>. The track-to-track measurement is the time required to move from one track to an adjacent track.<sup id="cite_ref-HDD_Glossary_5-3" class="reference"><a href="#cite_note-HDD_Glossary-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup> This is the shortest (fastest) possible seek time. In HDDs this is typically between 0.2 and 0.8 ms.<sup id="cite_ref-HP_SSD_16-0" class="reference"><a href="#cite_note-HP_SSD-16"><span class="cite-bracket">[</span>16<span class="cite-bracket">]</span></a></sup> The full stroke measurement is the time required to move from the outermost track to the innermost track. This is the longest (slowest) possible seek time.<sup id="cite_ref-RefGuide-Seek_7-2" class="reference"><a href="#cite_note-RefGuide-Seek-7"><span class="cite-bracket">[</span>7<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading4"><h4 id="Short_stroking">Short stroking</h4><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Hard_disk_drive_performance_characteristics&action=edit&section=4" title="Edit section: Short stroking"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p><i>Short stroking</i> is a term used in enterprise storage environments to describe an HDD that is purposely restricted in total capacity so that the actuator only has to move the heads across a smaller number of total tracks.<sup id="cite_ref-17" class="reference"><a href="#cite_note-17"><span class="cite-bracket">[</span>17<span class="cite-bracket">]</span></a></sup> This limits the maximum distance the heads can be from any point on the drive thereby reducing its average seek time, but also restricts the total capacity of the drive. This reduced seek time enables the HDD to increase the number of <a href="/wiki/IOPS" title="IOPS">IOPS</a> available from the drive. The cost and power per usable byte of storage rises as the maximum track range is reduced.<sup id="cite_ref-Auto6R-5_18-0" class="reference"><a href="#cite_note-Auto6R-5-18"><span class="cite-bracket">[</span>18<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-NullLobur2014_19-0" class="reference"><a href="#cite_note-NullLobur2014-19"><span class="cite-bracket">[</span>19<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading4"><h4 id="Effect_of_audible_noise_and_vibration_control">Effect of audible noise and vibration control</h4><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Hard_disk_drive_performance_characteristics&action=edit&section=5" title="Edit section: Effect of audible noise and vibration control"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Measured in <a href="/wiki/A-weighting" title="A-weighting">dBA</a>, audible noise is significant for certain applications, such as <a href="/wiki/Digital_video_recorder" title="Digital video recorder">DVRs</a>, digital audio recording and <a href="/wiki/Quiet_PC" title="Quiet PC">quiet computers</a>. Low noise disks typically use <a href="/wiki/Fluid_bearing" title="Fluid bearing">fluid bearings</a>, lower rotational speeds (usually 5,400 rpm) and reduce the seek speed under load (<a href="/wiki/Automatic_Acoustic_Management" class="mw-redirect" title="Automatic Acoustic Management">AAM</a>) to reduce audible clicks and crunching sounds. Drives in smaller form factors (e.g. 2.5 inch) are often quieter than larger drives.<sup id="cite_ref-RefGuide-Noise_20-0" class="reference"><a href="#cite_note-RefGuide-Noise-20"><span class="cite-bracket">[</span>20<span class="cite-bracket">]</span></a></sup> </p><p>Some desktop- and laptop-class disk drives allow the user to make a trade-off between seek performance and drive noise. For example, <a href="/wiki/Seagate_Technology" title="Seagate Technology">Seagate</a> offers a set of features in some drives called Sound Barrier Technology that include some user or system controlled noise and vibration reduction capability. Shorter seek times typically require more energy usage to quickly move the heads across the platter, causing loud noises from the pivot bearing and greater device vibrations as the heads are rapidly accelerated during the start of the seek motion and decelerated at the end of the seek motion. Quiet operation reduces movement speed and acceleration rates, but at a cost of reduced seek performance.<sup id="cite_ref-Auto6R-6_21-0" class="reference"><a href="#cite_note-Auto6R-6-21"><span class="cite-bracket">[</span>21<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Rotational_latency">Rotational latency</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Hard_disk_drive_performance_characteristics&action=edit&section=6" title="Edit section: Rotational latency"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <table class="wikitable floatright"> <caption>Typical HDD figures </caption> <tbody><tr> <th>HDD spindle<br />speed [rpm]</th> <th>Average<br />rotational<br />latency [ms] </th></tr> <tr align="right"> <td>4,200</td> <td>7.14 </td></tr> <tr align="right"> <td>5,400</td> <td>5.56 </td></tr> <tr align="right"> <td>7,200</td> <td>4.17 </td></tr> <tr align="right"> <td>10,000</td> <td>3.00 </td></tr> <tr align="right"> <td>15,000</td> <td>2.00 </td></tr></tbody></table> <p><i>Rotational latency</i> (sometimes called <i>rotational delay</i> or just <i>latency</i>) is the delay waiting for the <a href="/wiki/Rotation" title="Rotation">rotation</a> of the disk to bring the required <a href="/wiki/Disk_sector" title="Disk sector">disk sector</a> under the read-write head.<sup id="cite_ref-Auto6R-7_22-0" class="reference"><a href="#cite_note-Auto6R-7-22"><span class="cite-bracket">[</span>22<span class="cite-bracket">]</span></a></sup> It depends on the rotational speed of a disk (or <a href="/wiki/Hard_disk_drive#Spindle" title="Hard disk drive">spindle motor</a>), measured in <a href="/wiki/Revolutions_per_minute" title="Revolutions per minute">revolutions per minute</a> (RPM).<sup id="cite_ref-HDD_Glossary_5-4" class="reference"><a href="#cite_note-HDD_Glossary-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Auto6R-8_23-0" class="reference"><a href="#cite_note-Auto6R-8-23"><span class="cite-bracket">[</span>23<span class="cite-bracket">]</span></a></sup> For most magnetic media-based drives, the <i>average rotational latency</i> is typically based on the empirical relation that the average latency in milliseconds for such a drive is one-half the rotational period. <i>Maximum rotational latency</i> is the time it takes to do a full rotation excluding any <a href="/wiki/Spin-up" title="Spin-up">spin-up</a> time (as the relevant part of the disk may have just passed the head when the request arrived).<sup id="cite_ref-Scott_Lowe_24-0" class="reference"><a href="#cite_note-Scott_Lowe-24"><span class="cite-bracket">[</span>24<span class="cite-bracket">]</span></a></sup> </p> <ul><li><i><b>Maximum latency</b></i> <i>= 60/rpm</i></li> <li><i><b>Average latency</b></i> <i>= 0.5*Maximum latency</i></li></ul> <p>Therefore, the rotational latency and resulting access time can be improved (decreased) by increasing the rotational speed of the disks.<sup id="cite_ref-HDD_Glossary_5-5" class="reference"><a href="#cite_note-HDD_Glossary-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup> This also has the benefit of improving (increasing) the throughput (discussed later in this article). </p> <style data-mw-deduplicate="TemplateStyles:r1236090951">.mw-parser-output .hatnote{font-style:italic}.mw-parser-output div.hatnote{padding-left:1.6em;margin-bottom:0.5em}.mw-parser-output .hatnote i{font-style:normal}.mw-parser-output .hatnote+link+.hatnote{margin-top:-0.5em}@media print{body.ns-0 .mw-parser-output .hatnote{display:none!important}}</style><div role="note" class="hatnote navigation-not-searchable">Further information: <a href="/wiki/Disk_storage#CAV-CLV" title="Disk storage">Disk storage § CAV-CLV</a></div> <p>The spindle motor speed can use one of two types of disk rotation methods: 1) <a href="/wiki/Constant_linear_velocity" title="Constant linear velocity">constant linear velocity</a> (CLV), used mainly in optical storage, varies the rotational speed of the optical disc depending upon the position of the head, and 2) <a href="/wiki/Constant_angular_velocity" title="Constant angular velocity">constant angular velocity</a> (CAV), used in HDDs, standard FDDs, a few optical disc systems, and <a href="/wiki/Gramophone_record" class="mw-redirect" title="Gramophone record">vinyl audio records</a>, spins the media at one constant speed regardless of where the head is positioned. </p><p>Another wrinkle occurs depending on whether surface bit densities are constant. Usually, with a CAV spin rate, the densities are not constant so that the long outside tracks have the same number of bits as the shorter inside tracks. When the bit density is constant, outside tracks have more bits than inside tracks and is generally combined with a CLV spin rate. In both these schemes contiguous bit transfer rates are constant. This is not the case with other schemes such as using constant bit density with a CAV spin rate. </p> <div class="mw-heading mw-heading4"><h4 id="Effect_of_reduced_power_consumption">Effect of reduced power consumption</h4><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Hard_disk_drive_performance_characteristics&action=edit&section=7" title="Edit section: Effect of reduced power consumption"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p><a href="/wiki/Power_consumption" class="mw-redirect" title="Power consumption">Power consumption</a> has become increasingly important, not only in mobile devices such as laptops but also in server and desktop markets. Increasing data center machine density has led to problems delivering sufficient power to devices (especially for <a href="/wiki/Spin-up" title="Spin-up">spin-up</a>), and getting rid of the <a href="/wiki/Waste_heat" title="Waste heat">waste heat</a> subsequently produced, as well as environmental and electrical cost concerns (see <a href="/wiki/Green_computing" title="Green computing">green computing</a>). Most hard disk drives today support some form of power management which uses a number of specific power modes that save energy by reducing performance. When implemented, an HDD will change between a full power mode to one or more power saving modes as a function of drive usage. Recovery from the deepest mode, typically called Sleep where the drive is stopped or <a href="/wiki/Spin-up" title="Spin-up">spun down</a>, may take as long as several seconds to be fully operational thereby increasing the resulting latency.<sup id="cite_ref-Auto6R-9_25-0" class="reference"><a href="#cite_note-Auto6R-9-25"><span class="cite-bracket">[</span>25<span class="cite-bracket">]</span></a></sup> The drive manufacturers are also now producing <i>green drives</i> that include some additional features that do reduce power, but can adversely affect the latency including lower spindle speeds and parking heads off the media to reduce friction.<sup id="cite_ref-Auto6R-10_26-0" class="reference"><a href="#cite_note-Auto6R-10-26"><span class="cite-bracket">[</span>26<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Other">Other</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Hard_disk_drive_performance_characteristics&action=edit&section=8" title="Edit section: Other"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The <i><style data-mw-deduplicate="TemplateStyles:r1238216509">.mw-parser-output .vanchor>:target~.vanchor-text{background-color:#b1d2ff}@media screen{html.skin-theme-clientpref-night .mw-parser-output .vanchor>:target~.vanchor-text{background-color:#0f4dc9}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .vanchor>:target~.vanchor-text{background-color:#0f4dc9}}</style><span class="vanchor"><span id="command_processing_time"></span><span id="Command_processing_time"></span><span class="vanchor-text">command processing time</span></span></i> or <i>command overhead</i> is the time it takes for the drive electronics to set up the necessary communication between the various components in the device so it can read or write the data. This is of the order of 3 <a href="/wiki/Microsecond" title="Microsecond">μs</a>, very much less than other overhead times, so it is usually ignored when benchmarking hardware.<sup id="cite_ref-RedHat_2-2" class="reference"><a href="#cite_note-RedHat-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-RefGuide-Overhead_27-0" class="reference"><a href="#cite_note-RefGuide-Overhead-27"><span class="cite-bracket">[</span>27<span class="cite-bracket">]</span></a></sup> </p><p>The <i><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238216509"><span class="vanchor"><span id="settle_time"></span><span id="Settle_time"></span><span class="vanchor-text">settle time</span></span></i> is the time it takes the heads to <i>settle</i> on the target track and stop vibrating so they do not read or write <i>off track</i>. This time is usually very small, typically less than 100 μs, and modern HDD manufacturers account for it in their seek time specifications.<sup id="cite_ref-RefGuide-Settle_28-0" class="reference"><a href="#cite_note-RefGuide-Settle-28"><span class="cite-bracket">[</span>28<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading2"><h2 id="Data_transfer_rate">Data transfer rate</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Hard_disk_drive_performance_characteristics&action=edit&section=9" title="Edit section: Data transfer rate"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:HDD_read-write_benchmark_using_GNOME_Disks.png" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/b/b1/HDD_read-write_benchmark_using_GNOME_Disks.png/220px-HDD_read-write_benchmark_using_GNOME_Disks.png" decoding="async" width="220" height="166" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/b/b1/HDD_read-write_benchmark_using_GNOME_Disks.png/330px-HDD_read-write_benchmark_using_GNOME_Disks.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/b/b1/HDD_read-write_benchmark_using_GNOME_Disks.png/440px-HDD_read-write_benchmark_using_GNOME_Disks.png 2x" data-file-width="1280" data-file-height="967" /></a><figcaption>A plot showing dependency of transfer rate on cylinder</figcaption></figure> <p>The <i>data transfer rate</i> of a drive (also called <i>throughput</i>) covers both the internal rate (moving data between the disk surface and the controller on the drive) and the external rate (moving data between the controller on the drive and the host system). The measurable data transfer rate will be the lower (slower) of the two rates. The <i>sustained data transfer rate</i> or <i>sustained throughput</i> of a drive will be the lower of the sustained internal and sustained external rates. The sustained rate is less than or equal to the maximum or burst rate because it does not have the benefit of any cache or buffer memory in the drive. The internal rate is further determined by the media rate, sector overhead time, head switch time, and cylinder switch time.<sup id="cite_ref-HDD_Glossary_5-6" class="reference"><a href="#cite_note-HDD_Glossary-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-refGuide-Trans_29-0" class="reference"><a href="#cite_note-refGuide-Trans-29"><span class="cite-bracket">[</span>29<span class="cite-bracket">]</span></a></sup> </p> <dl><dt>Media rate</dt> <dd>Rate at which the drive can read bits from the surface of the media.</dd> <dt>Sector overhead time</dt> <dd>Additional time (bytes between sectors) needed for control structures and other information necessary to manage the drive, locate and validate data and perform other support functions.<sup id="cite_ref-RefGuide-Head-Switch_30-0" class="reference"><a href="#cite_note-RefGuide-Head-Switch-30"><span class="cite-bracket">[</span>30<span class="cite-bracket">]</span></a></sup></dd> <dt>Head switch time</dt> <dd>Additional time required to electrically switch from one head to another, re-align the head with the track and begin reading; only applies to multi-head drive and is about 1 to 2 ms.<sup id="cite_ref-RefGuide-Head-Switch_30-1" class="reference"><a href="#cite_note-RefGuide-Head-Switch-30"><span class="cite-bracket">[</span>30<span class="cite-bracket">]</span></a></sup></dd> <dt>Cylinder switch time</dt> <dd>Additional time required to move to the first track of the next cylinder and begin reading; the name cylinder is used because typically all the tracks of a drive with more than one head or data surface are read before moving the actuator. This time is typically about twice the track-to-track seek time. As of 2001, it was about 2 to 3 ms.<sup id="cite_ref-RefGuide-Cyl-Switch_31-0" class="reference"><a href="#cite_note-RefGuide-Cyl-Switch-31"><span class="cite-bracket">[</span>31<span class="cite-bracket">]</span></a></sup></dd></dl> <p>Data transfer rate (read/write) can be measured by writing a large file to disk using special file generator tools, then reading back the file. </p> <ul><li>According to vendor specifications sustained transfer rates up to 204 MB/s are available.<sup id="cite_ref-32" class="reference"><a href="#cite_note-32"><span class="cite-bracket">[</span>32<span class="cite-bracket">]</span></a></sup> As of 2010<sup class="plainlinks noexcerpt noprint asof-tag update" style="display:none;"><a class="external text" href="https://en.wikipedia.org/w/index.php?title=Hard_disk_drive_performance_characteristics&action=edit">[update]</a></sup>, a typical 7,200 RPM desktop HDD has a "disk-to-<a href="/wiki/Disk_buffer" title="Disk buffer">buffer</a>" data transfer rate up to 1030 Mbit/s.<sup id="cite_ref-Auto6R-11_33-0" class="reference"><a href="#cite_note-Auto6R-11-33"><span class="cite-bracket">[</span>33<span class="cite-bracket">]</span></a></sup> This rate depends on the track location, so it will be higher on the outer zones (where there are more data sectors per track) and lower on the inner zones (where there are fewer data sectors per track); and is generally somewhat higher for 10,000 RPM drives.</li> <li>Floppy disk drives have sustained "disk-to-<a href="/wiki/Disk_buffer" title="Disk buffer">buffer</a>" data transfer rates that are one or two orders of magnitude lower than that of HDDs.</li> <li>The sustained "disk-to-<a href="/wiki/Disk_buffer" title="Disk buffer">buffer</a>" data transfer rates varies amongst families of Optical disk drives with the slowest <a href="/wiki/CD-ROM#Transfer_rates" title="CD-ROM">1x CDs</a> at 1.23 Mbit/s floppy-like while a high performance <a href="/wiki/Blu-ray#Recording_speed" title="Blu-ray">12x Blu-ray drive</a> at 432 Mbit/s approaches the performance of HDDs.</li></ul> <p>A current widely used standard for the "buffer-to-computer" interface is 3.0 Gbit/s SATA, which can send about 300 megabyte/s (10-bit encoding) from the buffer to the computer, and thus is still comfortably ahead of today's disk-to-buffer transfer rates. </p><p>SSDs do not have the same internal limits of HDDs, so their internal and external transfer rates are often maximizing the capabilities of the drive-to-host interface. </p> <div class="mw-heading mw-heading3"><h3 id="Effect_of_file_system">Effect of file system</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Hard_disk_drive_performance_characteristics&action=edit&section=10" title="Edit section: Effect of file system"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Transfer rate can be influenced by <a href="/wiki/File_system_fragmentation" title="File system fragmentation">file system fragmentation</a> and the layout of the files. <a href="/wiki/Defragmentation" title="Defragmentation">Defragmentation</a> is a procedure used to minimize delay in retrieving data by moving related items to physically proximate areas on the disk.<sup id="cite_ref-itworld-2001-04-18_34-0" class="reference"><a href="#cite_note-itworld-2001-04-18-34"><span class="cite-bracket">[</span>34<span class="cite-bracket">]</span></a></sup> Some computer operating systems perform defragmentation automatically. Although automatic defragmentation is intended to reduce access delays, the procedure can slow response when performed while the computer is in use.<sup id="cite_ref-Auto6R-12_35-0" class="reference"><a href="#cite_note-Auto6R-12-35"><span class="cite-bracket">[</span>35<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Effect_of_areal_density">Effect of areal density</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Hard_disk_drive_performance_characteristics&action=edit&section=11" title="Edit section: Effect of areal density"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>HDD data transfer rate depends upon the rotational speed of the disks and the data recording density. Because heat and vibration limit rotational speed, increasing density has become the main method to improve sequential transfer rates.<sup id="cite_ref-RefGuide-Areal_36-0" class="reference"><a href="#cite_note-RefGuide-Areal-36"><span class="cite-bracket">[</span>36<span class="cite-bracket">]</span></a></sup> <i><a href="/wiki/Areal_density_(computer_storage)" class="mw-redirect" title="Areal density (computer storage)">Areal density</a></i> (the number of bits that can be stored in a certain area of the disk) has been increased over time by increasing both the number of tracks across the disk, and the number of sectors per track. The latter will increase the data transfer rate for a given RPM speed. Improvement of data transfer rate performance is correlated to the areal density only by increasing a track's linear surface bit density (sectors per track). Simply increasing the number of tracks on a disk can affect seek times but not gross transfer rates. According to industry observers and analysts for 2011 to 2016,<sup id="cite_ref-isuppli2012_37-0" class="reference"><a href="#cite_note-isuppli2012-37"><span class="cite-bracket">[</span>37<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Dave_Anderson_2013_38-0" class="reference"><a href="#cite_note-Dave_Anderson_2013-38"><span class="cite-bracket">[</span>38<span class="cite-bracket">]</span></a></sup> “The current roadmap predicts no more than a 20%/yr improvement in bit density”.<sup id="cite_ref-Rosenthal2012_39-0" class="reference"><a href="#cite_note-Rosenthal2012-39"><span class="cite-bracket">[</span>39<span class="cite-bracket">]</span></a></sup> Seek times have not kept up with throughput increases, which themselves have not kept up with growth in bit density and storage capacity. </p> <div class="mw-heading mw-heading3"><h3 id="Interleave">Interleave</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Hard_disk_drive_performance_characteristics&action=edit&section=12" title="Edit section: Interleave"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:IBM_PC_XT_10_meg_MFM_low_level_format.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/en/thumb/8/83/IBM_PC_XT_10_meg_MFM_low_level_format.jpg/220px-IBM_PC_XT_10_meg_MFM_low_level_format.jpg" decoding="async" width="220" height="200" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/en/thumb/8/83/IBM_PC_XT_10_meg_MFM_low_level_format.jpg/330px-IBM_PC_XT_10_meg_MFM_low_level_format.jpg 1.5x, //upload.wikimedia.org/wikipedia/en/8/83/IBM_PC_XT_10_meg_MFM_low_level_format.jpg 2x" data-file-width="331" data-file-height="301" /></a><figcaption>Low-level formatting software from 1987 to find highest performance interleave choice for <span class="nowrap">10 <a href="/wiki/Megabyte" title="Megabyte">MB</a></span> <span class="nowrap">IBM PC XT</span> hard disk drive</figcaption></figure> <p>Sector interleave is a mostly obsolete device characteristic related to data rate, dating back to when computers were too slow to be able to read large continuous streams of data. Interleaving introduced gaps between data sectors to allow time for slow equipment to get ready to read the next block of data. Without interleaving, the next logical sector would arrive at the read/write head before the equipment was ready, requiring the system to wait for another complete disk revolution before reading could be performed. </p><p>However, because interleaving introduces intentional physical delays between blocks of data thereby lowering the data rate, setting the interleave to a ratio higher than required causes unnecessary delays for equipment that has the performance needed to read sectors more quickly. The interleaving ratio was therefore usually chosen by the end-user to suit their particular computer system's performance capabilities when the drive was first installed in their system. </p><p>Modern technology is capable of reading data as fast as it can be obtained from the spinning platters, so interleaving is no longer used. </p> <div class="mw-heading mw-heading2"><h2 id="Power_consumption">Power consumption</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Hard_disk_drive_performance_characteristics&action=edit&section=13" title="Edit section: Power consumption"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p><a href="/wiki/Power_consumption" class="mw-redirect" title="Power consumption">Power consumption</a> has become increasingly important, not only in mobile devices such as laptops but also in server and desktop markets. Increasing data center machine density has led to problems delivering sufficient power to devices (especially for spin up), and getting rid of the waste heat subsequently produced, as well as environmental and electrical cost concerns (see <a href="/wiki/Green_computing" title="Green computing">green computing</a>). Heat dissipation is tied directly to power consumption, and as drives age, disk <a href="/wiki/Failure_rate" title="Failure rate">failure rates</a> increase at higher drive temperatures.<sup id="cite_ref-xbit-2007-12-06_40-0" class="reference"><a href="#cite_note-xbit-2007-12-06-40"><span class="cite-bracket">[</span>40<span class="cite-bracket">]</span></a></sup> Similar issues exist for large companies with thousands of desktop PCs. Smaller form factor drives often use less power than larger drives. One interesting development in this area is actively controlling the seek speed so that the head arrives at its destination only just in time to read the sector, rather than arriving as quickly as possible and then having to wait for the sector to come around (i.e. the rotational latency).<sup id="cite_ref-AutoMK-73_41-0" class="reference"><a href="#cite_note-AutoMK-73-41"><span class="cite-bracket">[</span>41<span class="cite-bracket">]</span></a></sup> Many of the hard drive companies are now producing Green Drives that require much less power and cooling. Many of these Green Drives spin slower (<5,400 rpm compared to 7,200, 10,000 or 15,000 rpm) thereby generating less heat. Power consumption can also be reduced by parking the drive heads when the disk is not in use reducing friction, adjusting spin speeds,<sup id="cite_ref-AutoMK-74_42-0" class="reference"><a href="#cite_note-AutoMK-74-42"><span class="cite-bracket">[</span>42<span class="cite-bracket">]</span></a></sup> and disabling internal components when not in use.<sup id="cite_ref-AutoMK-75_43-0" class="reference"><a href="#cite_note-AutoMK-75-43"><span class="cite-bracket">[</span>43<span class="cite-bracket">]</span></a></sup> </p><p>Drives use more power, briefly, when starting up (spin-up). Although this has little direct effect on total energy consumption, the maximum power demanded from the power supply, and hence its required rating, can be reduced in systems with several drives by controlling when they spin up. </p> <ul><li>On SCSI hard disk drives, the SCSI controller can directly control spin up and spin down of the drives.</li> <li>Some <a href="/wiki/Parallel_ATA" title="Parallel ATA">Parallel ATA</a> (PATA) and <a href="/wiki/Serial_ATA" class="mw-redirect" title="Serial ATA">Serial ATA</a> (SATA) hard disk drives support <a href="/w/index.php?title=Power-up_in_standby&action=edit&redlink=1" class="new" title="Power-up in standby (page does not exist)">power-up in standby</a> (PUIS): each drive does not spin up until the controller or system BIOS issues a specific command to do so. This allows the system to be set up to stagger disk start-up and limit maximum power demand at switch-on.</li> <li>Some SATA II and later hard disk drives support <a href="/wiki/Staggered_spinup" class="mw-redirect" title="Staggered spinup">staggered spin-up</a>, allowing the computer to spin up the drives in sequence to reduce load on the power supply when booting.<sup id="cite_ref-AutoMK-76_44-0" class="reference"><a href="#cite_note-AutoMK-76-44"><span class="cite-bracket">[</span>44<span class="cite-bracket">]</span></a></sup></li></ul> <p>Most hard disk drives today support some form of power management which uses a number of specific power modes that save energy by reducing performance. When implemented an HDD will change between a full power mode to one or more power saving modes as a function of drive usage. Recovery from the deepest mode, typically called Sleep, may take as long as several seconds.<sup id="cite_ref-AutoMK-77_45-0" class="reference"><a href="#cite_note-AutoMK-77-45"><span class="cite-bracket">[</span>45<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading2"><h2 id="Shock_resistance">Shock resistance</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Hard_disk_drive_performance_characteristics&action=edit&section=14" title="Edit section: Shock resistance"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Shock resistance is especially important for mobile devices. Some laptops now include <a href="/wiki/Active_hard_drive_protection" class="mw-redirect" title="Active hard drive protection">active hard drive protection</a> that parks the disk heads if the machine is dropped, hopefully before impact, to offer the greatest possible chance of survival in such an event. Maximum shock tolerance to date is 350 <a href="/wiki/Gravitational_acceleration" title="Gravitational acceleration">g</a> for operating and 1,000 g for non-operating.<sup id="cite_ref-AutoMK-78_46-0" class="reference"><a href="#cite_note-AutoMK-78-46"><span class="cite-bracket">[</span>46<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading2"><h2 id="SMR_drives">SMR drives</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Hard_disk_drive_performance_characteristics&action=edit&section=15" title="Edit section: SMR drives"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <style data-mw-deduplicate="TemplateStyles:r1251242444">.mw-parser-output .ambox{border:1px solid #a2a9b1;border-left:10px solid #36c;background-color:#fbfbfb;box-sizing:border-box}.mw-parser-output .ambox+link+.ambox,.mw-parser-output .ambox+link+style+.ambox,.mw-parser-output .ambox+link+link+.ambox,.mw-parser-output .ambox+.mw-empty-elt+link+.ambox,.mw-parser-output .ambox+.mw-empty-elt+link+style+.ambox,.mw-parser-output .ambox+.mw-empty-elt+link+link+.ambox{margin-top:-1px}html body.mediawiki .mw-parser-output .ambox.mbox-small-left{margin:4px 1em 4px 0;overflow:hidden;width:238px;border-collapse:collapse;font-size:88%;line-height:1.25em}.mw-parser-output .ambox-speedy{border-left:10px solid #b32424;background-color:#fee7e6}.mw-parser-output .ambox-delete{border-left:10px solid #b32424}.mw-parser-output .ambox-content{border-left:10px solid #f28500}.mw-parser-output .ambox-style{border-left:10px solid #fc3}.mw-parser-output .ambox-move{border-left:10px solid #9932cc}.mw-parser-output .ambox-protection{border-left:10px solid #a2a9b1}.mw-parser-output .ambox .mbox-text{border:none;padding:0.25em 0.5em;width:100%}.mw-parser-output .ambox .mbox-image{border:none;padding:2px 0 2px 0.5em;text-align:center}.mw-parser-output .ambox .mbox-imageright{border:none;padding:2px 0.5em 2px 0;text-align:center}.mw-parser-output .ambox .mbox-empty-cell{border:none;padding:0;width:1px}.mw-parser-output .ambox .mbox-image-div{width:52px}@media(min-width:720px){.mw-parser-output .ambox{margin:0 10%}}@media print{body.ns-0 .mw-parser-output .ambox{display:none!important}}</style><table class="box-Expand_section plainlinks metadata ambox mbox-small-left ambox-content" role="presentation"><tbody><tr><td class="mbox-image"><span typeof="mw:File"><a href="/wiki/File:Wiki_letter_w_cropped.svg" class="mw-file-description"><img alt="[icon]" src="//upload.wikimedia.org/wikipedia/commons/thumb/1/1c/Wiki_letter_w_cropped.svg/20px-Wiki_letter_w_cropped.svg.png" decoding="async" width="20" height="14" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/1/1c/Wiki_letter_w_cropped.svg/30px-Wiki_letter_w_cropped.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/1/1c/Wiki_letter_w_cropped.svg/40px-Wiki_letter_w_cropped.svg.png 2x" data-file-width="44" data-file-height="31" /></a></span></td><td class="mbox-text"><div class="mbox-text-span">This section <b>needs expansion</b>. You can help by <a class="external text" href="https://en.wikipedia.org/w/index.php?title=Hard_disk_drive_performance_characteristics&action=edit&section=">adding to it</a>. <span class="date-container"><i>(<span class="date">November 2020</span>)</i></span></div></td></tr></tbody></table> <p>Hard drives that use <a href="/wiki/Shingled_magnetic_recording" title="Shingled magnetic recording">shingled magnetic recording</a> (SMR) differ significantly in write performance characteristics from conventional (CMR) drives. In particular, sustained random writes are significantly slower on SMR drives.<sup id="cite_ref-47" class="reference"><a href="#cite_note-47"><span class="cite-bracket">[</span>47<span class="cite-bracket">]</span></a></sup> As SMR technology causes a degradation on write performance, some new HDD with Hybrid SMR technology (making it possible to adjust the ratio of SMR part and CMR part dynamically) may have various characteristics under different SMR/CMR ratios.<sup id="cite_ref-48" class="reference"><a href="#cite_note-48"><span class="cite-bracket">[</span>48<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading2"><h2 id="Comparison_to_solid-state_drives">Comparison to solid-state drives</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Hard_disk_drive_performance_characteristics&action=edit&section=16" title="Edit section: Comparison to solid-state drives"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/wiki/Solid-state_drive#Comparison_with_other_technologies" title="Solid-state drive">Solid-state drive § Comparison with other technologies</a></div> <p><a href="/wiki/Solid-state_drive" title="Solid-state drive">Solid-state devices</a> (SSDs) do not have moving parts. Most attributes related to the movement of <a href="/wiki/Mechanical_device" class="mw-redirect" title="Mechanical device">mechanical components</a> are not applicable in measuring their performance, but they are affected by some electrically based elements that causes a measurable access delay.<sup id="cite_ref-Auto6R-1_49-0" class="reference"><a href="#cite_note-Auto6R-1-49"><span class="cite-bracket">[</span>49<span class="cite-bracket">]</span></a></sup> </p><p>Measurement of seek time is only testing electronic circuits preparing a particular location on the memory in the storage device. Typical SSDs will have a seek time between 0.08 and 0.16 ms.<sup id="cite_ref-HP_SSD_16-1" class="reference"><a href="#cite_note-HP_SSD-16"><span class="cite-bracket">[</span>16<span class="cite-bracket">]</span></a></sup> </p><p>Flash memory-based SSDs do not need defragmentation. However, because file systems <a href="/wiki/Write_amplification" title="Write amplification">write pages of data</a> that are smaller (2K, 4K, 8K, or 16K) than the blocks of data managed by the SSD (from 256 KB to 4 MB, hence 128 to 256 pages per block),<sup id="cite_ref-50" class="reference"><a href="#cite_note-50"><span class="cite-bracket">[</span>50<span class="cite-bracket">]</span></a></sup> over time, an SSD's write performance can degrade as the drive becomes full of pages which are partial or no longer needed by the file system. This can be ameliorated by a <a href="/wiki/Trim_(computing)" title="Trim (computing)">TRIM</a> command from the system or internal <a href="/wiki/Garbage_collection_(SSD)" class="mw-redirect" title="Garbage collection (SSD)">garbage collection</a>. Flash memory wears out over time as it is repeatedly written to; the writes required by defragmentation wear the drive for no speed advantage.<sup id="cite_ref-Auto6R-13_51-0" class="reference"><a href="#cite_note-Auto6R-13-51"><span class="cite-bracket">[</span>51<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading2"><h2 id="See_also">See also</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Hard_disk_drive_performance_characteristics&action=edit&section=17" title="Edit section: See also"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <ul><li><a href="/wiki/VRPM" title="VRPM">vRPM</a></li> <li><a href="/wiki/Hybrid_drive" title="Hybrid drive">Hybrid drive</a></li> <li><a href="/wiki/IOPS" title="IOPS">IOPS</a></li> <li><a href="/wiki/Standard_RAID_levels" title="Standard RAID levels">Standard RAID levels</a></li></ul> <div class="mw-heading mw-heading2"><h2 id="References">References</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Hard_disk_drive_performance_characteristics&action=edit&section=18" title="Edit section: References"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <style data-mw-deduplicate="TemplateStyles:r1239543626">.mw-parser-output .reflist{margin-bottom:0.5em;list-style-type:decimal}@media screen{.mw-parser-output .reflist{font-size:90%}}.mw-parser-output .reflist .references{font-size:100%;margin-bottom:0;list-style-type:inherit}.mw-parser-output .reflist-columns-2{column-width:30em}.mw-parser-output .reflist-columns-3{column-width:25em}.mw-parser-output .reflist-columns{margin-top:0.3em}.mw-parser-output .reflist-columns ol{margin-top:0}.mw-parser-output .reflist-columns li{page-break-inside:avoid;break-inside:avoid-column}.mw-parser-output .reflist-upper-alpha{list-style-type:upper-alpha}.mw-parser-output .reflist-upper-roman{list-style-type:upper-roman}.mw-parser-output .reflist-lower-alpha{list-style-type:lower-alpha}.mw-parser-output .reflist-lower-greek{list-style-type:lower-greek}.mw-parser-output .reflist-lower-roman{list-style-type:lower-roman}</style><div class="reflist reflist-columns references-column-width" style="column-width: 30em;"> <ol class="references"> <li id="cite_note-PCTechGuide-1"><span class="mw-cite-backlink"><b><a href="#cite_ref-PCTechGuide_1-0">^</a></b></span> <span class="reference-text"><style data-mw-deduplicate="TemplateStyles:r1238218222">.mw-parser-output cite.citation{font-style:inherit;word-wrap:break-word}.mw-parser-output .citation q{quotes:"\"""\"""'""'"}.mw-parser-output .citation:target{background-color:rgba(0,127,255,0.133)}.mw-parser-output .id-lock-free.id-lock-free a{background:url("//upload.wikimedia.org/wikipedia/commons/6/65/Lock-green.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-limited.id-lock-limited a,.mw-parser-output .id-lock-registration.id-lock-registration a{background:url("//upload.wikimedia.org/wikipedia/commons/d/d6/Lock-gray-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-subscription.id-lock-subscription a{background:url("//upload.wikimedia.org/wikipedia/commons/a/aa/Lock-red-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .cs1-ws-icon a{background:url("//upload.wikimedia.org/wikipedia/commons/4/4c/Wikisource-logo.svg")right 0.1em center/12px no-repeat}body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-free a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-limited a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-registration a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-subscription a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .cs1-ws-icon a{background-size:contain;padding:0 1em 0 0}.mw-parser-output .cs1-code{color:inherit;background:inherit;border:none;padding:inherit}.mw-parser-output .cs1-hidden-error{display:none;color:var(--color-error,#d33)}.mw-parser-output .cs1-visible-error{color:var(--color-error,#d33)}.mw-parser-output .cs1-maint{display:none;color:#085;margin-left:0.3em}.mw-parser-output .cs1-kern-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right{padding-right:0.2em}.mw-parser-output .citation .mw-selflink{font-weight:inherit}@media screen{.mw-parser-output .cs1-format{font-size:95%}html.skin-theme-clientpref-night .mw-parser-output .cs1-maint{color:#18911f}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .cs1-maint{color:#18911f}}</style><cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://www.pctechguide.com/hard-disk-hard-drive-performance-transfer-rates-latency-and-seek-times">"Hard Disk (Hard Drive) Performance – transfer rates, latency and seek times"</a>. pctechguide.com<span class="reference-accessdate">. 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Retrieved <span class="nowrap">2011-07-04</span></span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=IBM+Archives+%E2%80%93+IBM+3350+direct+access+storage&rft.pub=IBM&rft.date=2003-01-23&rft_id=http%3A%2F%2Fwww-03.ibm.com%2Fibm%2Fhistory%2Fexhibits%2Fstorage%2Fstorage_3350.html&rfr_id=info%3Asid%2Fen.wikipedia.org%3AHard+disk+drive+performance+characteristics" class="Z3988"></span></span> </li> <li id="cite_note-14"><span class="mw-cite-backlink"><b><a href="#cite_ref-14">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFAnand_Lal_Shimpi2010" class="citation web cs1">Anand Lal Shimpi (April 6, 2010). <a rel="nofollow" class="external text" href="http://www.anandtech.com/show/3636/western-digitals-new-velociraptor-vr200m-10k-rpm-at-450gb-and-600gb">"Western Digital's New VelociRaptor VR200M: 10K RPM at 450GB and 600GB"</a>. <i>anandtech.com</i><span class="reference-accessdate">. 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June 2010. Archived from <a rel="nofollow" class="external text" href="http://www.wdc.com/en/products/products.aspx?id=140">the original</a> on 2011-01-05<span class="reference-accessdate">. Retrieved <span class="nowrap">2011-01-15</span></span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=WD+Scorpio+Blue+Mobile%3A+Drive+Specifications&rft.pub=Western+Digital&rft.date=2010-06&rft_id=http%3A%2F%2Fwww.wdc.com%2Fen%2Fproducts%2Fproducts.aspx%3Fid%3D140&rfr_id=info%3Asid%2Fen.wikipedia.org%3AHard+disk+drive+performance+characteristics" class="Z3988"></span></span> </li> <li id="cite_note-HP_SSD-16"><span class="mw-cite-backlink">^ <a href="#cite_ref-HP_SSD_16-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-HP_SSD_16-1"><sup><i><b>b</b></i></sup></a></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://h41112.www4.hp.com/promo/blades-community/eur/en/library/weekly_comment/081027_HP-SSD-part2-v2_clean.pdf">"Understanding Solid State Drives (part two – performance)"</a> <span class="cs1-format">(PDF)</span>. <a href="/wiki/Hewlett-Packard" title="Hewlett-Packard">HP</a>. 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Retrieved <span class="nowrap">July 6,</span> 2011</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=Understanding+Solid+State+Drives+%28part+two+%E2%80%93+performance%29&rft.pub=HP&rft.date=2008-10-27&rft_id=http%3A%2F%2Fh41112.www4.hp.com%2Fpromo%2Fblades-community%2Feur%2Fen%2Flibrary%2Fweekly_comment%2F081027_HP-SSD-part2-v2_clean.pdf&rfr_id=info%3Asid%2Fen.wikipedia.org%3AHard+disk+drive+performance+characteristics" class="Z3988"></span></span> </li> <li id="cite_note-17"><span class="mw-cite-backlink"><b><a href="#cite_ref-17">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://www.tomshardware.com/reviews/short-stroking-hdd,2157.html">"Accelerate Your Hard Drive By Short Stroking"</a>. <i>Tom's Hardware</i>. 5 March 2009.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=Tom%27s+Hardware&rft.atitle=Accelerate+Your+Hard+Drive+By+Short+Stroking&rft.date=2009-03-05&rft_id=https%3A%2F%2Fwww.tomshardware.com%2Freviews%2Fshort-stroking-hdd%2C2157.html&rfr_id=info%3Asid%2Fen.wikipedia.org%3AHard+disk+drive+performance+characteristics" class="Z3988"></span></span> </li> <li id="cite_note-Auto6R-5-18"><span class="mw-cite-backlink"><b><a href="#cite_ref-Auto6R-5_18-0">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFSchmidRoos2009" class="citation web cs1">Schmid, Patrick; Roos, Achim (2009-03-05). <a rel="nofollow" class="external text" href="http://www.tomshardware.com/reviews/short-stroking-hdd,2157.html">"Accelerate Your Hard Drive By Short Stroking"</a>. tomshardware.com<span class="reference-accessdate">. Retrieved <span class="nowrap">2011-07-05</span></span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=Accelerate+Your+Hard+Drive+By+Short+Stroking&rft.pub=tomshardware.com&rft.date=2009-03-05&rft.aulast=Schmid&rft.aufirst=Patrick&rft.au=Roos%2C+Achim&rft_id=http%3A%2F%2Fwww.tomshardware.com%2Freviews%2Fshort-stroking-hdd%2C2157.html&rfr_id=info%3Asid%2Fen.wikipedia.org%3AHard+disk+drive+performance+characteristics" class="Z3988"></span></span> </li> <li id="cite_note-NullLobur2014-19"><span class="mw-cite-backlink"><b><a href="#cite_ref-NullLobur2014_19-0">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFNullLobur2014" class="citation book cs1">Null, Linda; Lobur, Julia (14 February 2014). <a rel="nofollow" class="external text" href="https://books.google.com/books?id=GKgxDwAAQBAJ&pg=PT499"><i>The Essentials of Computer Organization and Architecture</i></a>. Jones & Bartlett Learning. pp. <span class="nowrap">499–</span>500. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/978-1-284-15077-3" title="Special:BookSources/978-1-284-15077-3"><bdi>978-1-284-15077-3</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=The+Essentials+of+Computer+Organization+and+Architecture&rft.pages=%3Cspan+class%3D%22nowrap%22%3E499-%3C%2Fspan%3E500&rft.pub=Jones+%26+Bartlett+Learning&rft.date=2014-02-14&rft.isbn=978-1-284-15077-3&rft.aulast=Null&rft.aufirst=Linda&rft.au=Lobur%2C+Julia&rft_id=https%3A%2F%2Fbooks.google.com%2Fbooks%3Fid%3DGKgxDwAAQBAJ%26pg%3DPT499&rfr_id=info%3Asid%2Fen.wikipedia.org%3AHard+disk+drive+performance+characteristics" class="Z3988"></span></span> </li> <li id="cite_note-RefGuide-Noise-20"><span class="mw-cite-backlink"><b><a href="#cite_ref-RefGuide-Noise_20-0">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFKozierok2001" class="citation web cs1">Kozierok, Charles (2001-04-17). <a rel="nofollow" class="external text" href="https://web.archive.org/web/20120101162803/http://www.pcguide.com/ref/hdd/perf/qual/issuesNoise-c.html">"Noise and Vibration"</a>. pcguide.com. Archived from <a rel="nofollow" class="external text" href="http://pcguide.com/ref/hdd/perf/qual/issuesNoise-c.html">the original</a> on 2012-01-01<span class="reference-accessdate">. Retrieved <span class="nowrap">2012-04-04</span></span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=Noise+and+Vibration&rft.pub=pcguide.com&rft.date=2001-04-17&rft.aulast=Kozierok&rft.aufirst=Charles&rft_id=http%3A%2F%2Fpcguide.com%2Fref%2Fhdd%2Fperf%2Fqual%2FissuesNoise-c.html&rfr_id=info%3Asid%2Fen.wikipedia.org%3AHard+disk+drive+performance+characteristics" class="Z3988"></span></span> </li> <li id="cite_note-Auto6R-6-21"><span class="mw-cite-backlink"><b><a href="#cite_ref-Auto6R-6_21-0">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://web.archive.org/web/20120324185420/http://www.seagate.com/docs/pdf/whitepaper/sound_barrier.pdf">"Seagate's Sound Barrier Technology"</a> <span class="cs1-format">(PDF)</span>. November 2000. 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Retrieved <span class="nowrap">2011-07-06</span></span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=Seagate%27s+Sound+Barrier+Technology&rft.date=2000-11&rft_id=http%3A%2F%2Fwww.seagate.com%2Fdocs%2Fpdf%2Fwhitepaper%2Fsound_barrier.pdf&rfr_id=info%3Asid%2Fen.wikipedia.org%3AHard+disk+drive+performance+characteristics" class="Z3988"></span></span> </li> <li id="cite_note-Auto6R-7-22"><span class="mw-cite-backlink"><b><a href="#cite_ref-Auto6R-7_22-0">^</a></b></span> <span class="reference-text">In the 1950s and 1960s magnetic data storage devices used a <a href="/wiki/Drum_memory" title="Drum memory">drum</a> instead of flat discs.</span> </li> <li id="cite_note-Auto6R-8-23"><span class="mw-cite-backlink"><b><a href="#cite_ref-Auto6R-8_23-0">^</a></b></span> <span class="reference-text">In some early PCs the internal bus was slower than the drive data rate so sectors would be missed resulting in the loss of an entire revolution. To prevent this sectors were <a href="/wiki/Interleaving_(disk_storage)" title="Interleaving (disk storage)">interleaved</a> to slow the effective data rate preventing missed sectors. This is no longer a problem for current PCs and storage devices.</span> </li> <li id="cite_note-Scott_Lowe-24"><span class="mw-cite-backlink"><b><a href="#cite_ref-Scott_Lowe_24-0">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFLowe2010" class="citation web cs1">Lowe, Scott (2010-02-12). <a rel="nofollow" class="external text" href="https://www.techrepublic.com/blog/datacenter/calculate-iops-in-a-storage-array/2182">"Calculate IOPS in a storage array"</a>. techrepublic.com<span class="reference-accessdate">. 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Retrieved <span class="nowrap">2011-07-06</span></span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=Momentus+5400.5+SATA+3Gb%2Fs+320-GB+Hard+Drive&rft_id=http%3A%2F%2Fwww.seagate.com%2Fww%2Fv%2Findex.jsp%3Fvgnextoid%3D5fb658a3fd20a110VgnVCM100000f5ee0a0aRCRD&rfr_id=info%3Asid%2Fen.wikipedia.org%3AHard+disk+drive+performance+characteristics" class="Z3988"></span></span> </li> <li id="cite_note-RefGuide-Overhead-27"><span class="mw-cite-backlink"><b><a href="#cite_ref-RefGuide-Overhead_27-0">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFKozierok2001" class="citation web cs1">Kozierok, Charles (2001-04-17). <a rel="nofollow" class="external text" href="https://web.archive.org/web/20120419165013/http://www.pcguide.com/ref/hdd/perf/perf/spec/posOverhead-c.html">"Command Overhead Time"</a>. pcguide.com. 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Retrieved <span class="nowrap">2012-04-04</span></span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=Command+Overhead+Time&rft.pub=pcguide.com&rft.date=2001-04-17&rft.aulast=Kozierok&rft.aufirst=Charles&rft_id=http%3A%2F%2Fpcguide.com%2Fref%2Fhdd%2Fperf%2Fperf%2Fspec%2FposOverhead-c.html&rfr_id=info%3Asid%2Fen.wikipedia.org%3AHard+disk+drive+performance+characteristics" class="Z3988"></span></span> </li> <li id="cite_note-RefGuide-Settle-28"><span class="mw-cite-backlink"><b><a href="#cite_ref-RefGuide-Settle_28-0">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFKozierok2001" class="citation web cs1">Kozierok, Charles (2001-04-17). <a rel="nofollow" class="external text" href="https://web.archive.org/web/20120108061506/http://www.pcguide.com/ref/hdd/perf/perf/spec/posSettle-c.html">"Settle Time"</a>. pcguide.com. 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Retrieved <span class="nowrap">2012-04-04</span></span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=Settle+Time&rft.pub=pcguide.com&rft.date=2001-04-17&rft.aulast=Kozierok&rft.aufirst=Charles&rft_id=http%3A%2F%2Fpcguide.com%2Fref%2Fhdd%2Fperf%2Fperf%2Fspec%2FposSettle-c.html&rfr_id=info%3Asid%2Fen.wikipedia.org%3AHard+disk+drive+performance+characteristics" class="Z3988"></span></span> </li> <li id="cite_note-refGuide-Trans-29"><span class="mw-cite-backlink"><b><a href="#cite_ref-refGuide-Trans_29-0">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFKozierok2001" class="citation web cs1">Kozierok, Charles (2001-04-17). <a rel="nofollow" class="external text" href="https://web.archive.org/web/20120320185116/http://www.pcguide.com/ref/hdd/perf/perf/spec/trans.htm">"Transfer Performance Specifications"</a>. pcguide.com. 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