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<title>Disk controller</title>

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

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</style><div role="note" class="hatnote navigation-not-searchable">Not to be confused with <a href="Host_adapter" title="Host adapter">Host adapter</a>.</div>

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<p>A <b>disk controller</b> is a controller <a href="Electronic_circuit" title="Electronic circuit">circuit</a> that enables a <a href="CPU" class="mw-redirect" title="CPU">CPU</a> to communicate with a <a href="Hard_disk" class="mw-redirect" title="Hard disk">hard disk</a>, <a href="Floppy_disk" title="Floppy disk">floppy disk</a> or other kind of <a href="Disk_drive" class="mw-redirect" title="Disk drive">disk drive</a>. It also provides an interface between the disk drive and the bus connecting it to the rest of the system.<sup id="cite_ref-1" class="reference"><a href="#cite_note-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-2" class="reference"><a href="#cite_note-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup>

</p><p>Early disk controllers were identified by their storage methods and data encoding. They were typically implemented on a separate controller card. <a href="Modified_frequency_modulation" title="Modified frequency modulation">Modified frequency modulation</a> (MFM) controllers were the most common type in small computers, used for both floppy disk and hard disk drives. <a href="Run_length_limited" class="mw-redirect" title="Run length limited">Run length limited</a> (RLL) controllers used data compression to increase storage capacity by about 50%. <a href="Priam_Corporation" title="Priam Corporation"> Priam</a> created a proprietary storage algorithm that could double the disk storage. <a href="Shugart_Associates" title="Shugart Associates">Shugart Associates</a> Systems Interface (<a href="Shugart_Associates_System_Interface" class="mw-redirect" title="Shugart Associates System Interface">SASI</a>) was a predecessor to <a href="SCSI" title="SCSI">SCSI</a>.

</p><p>Modern disk controllers are integrated into the disk drive as peripheral controllers. For example, <i>SCSI disks</i> have built-in SCSI controllers. In the past, before most SCSI controller functionality was implemented in a single chip, separate SCSI controllers interfaced disks to the SCSI bus.

</p><p>These integrated peripheral controllers communicate with a <a href="Host_adapter" title="Host adapter">host adapter</a> in the host system over a standardized, high-level storage bus interface. The most common types of interfaces provided nowadays by host controllers are <a href="Parallel_ATA" title="Parallel ATA">PATA (IDE)</a> and <a href="Serial_ATA" class="mw-redirect" title="Serial ATA">Serial ATA</a> for home use. High-end disks use <a href="Parallel_SCSI" title="Parallel SCSI">Parallel SCSI</a>, <a href="Fibre_Channel" title="Fibre Channel">Fibre Channel</a> or <a href="Serial_Attached_SCSI" title="Serial Attached SCSI">Serial Attached SCSI</a>. The peripheral controller integrated on <a href="Parallel_ATA" title="Parallel ATA">PATA (IDE)</a>, <a href="Serial_ATA" class="mw-redirect" title="Serial ATA">Serial ATA</a>, <a href="Parallel_SCSI" title="Parallel SCSI">Parallel SCSI</a> or <a href="Serial_Attached_SCSI" title="Serial Attached SCSI">Serial Attached SCSI</a> hard disk is usually a <a href="Microcontroller" title="Microcontroller">microcontroller</a> or an <a href="ASIC" class="mw-redirect" title="ASIC">ASIC</a>.

</p><p>Disk controllers can also control the timing of access to <a href="Flash_memory" title="Flash memory">flash memory</a>, which is not mechanical in nature (i.e. no spinning disk).

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<div class="mw-heading mw-heading2"><h2 id="Disk_controller_versus_host_adapter">Disk controller versus host adapter</h2></div>

<p>The component that allows a <i>computer</i> to talk to a peripheral bus is a <a href="Host_adapter" title="Host adapter">host adapter</a> or host bus adapter (HBA, e.g. <a href="Advanced_Host_Controller_Interface" title="Advanced Host Controller Interface">Advanced Host Controller Interface</a> or AHDC). A disk controller allows a <i>disk</i> to talk to the same bus. Signals read by a <a href="Disk_read-and-write_head" title="Disk read-and-write head">disk read-and-write head</a> are converted by a disk controller, then transmitted over the peripheral bus, then converted again by the host adapter into the suitable format for the <a href="Motherboard" title="Motherboard">motherboard</a>'s bus, and then read by the <a href="CPU" class="mw-redirect" title="CPU">CPU</a> into the memory (RAM).

</p><p>Sometimes there may be yet another controller between a host adapter and a disk controller - a <a href="Disk_array_controller" title="Disk array controller">disk array controller</a> that allows <a href="RAID#Hardware-based" title="RAID">hardware RAID</a> to be formed. Sometimes it may be even physically integrated with an HBA.

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

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</style><span class="citation foldoc">This article is based on material taken from <a rel="nofollow" class="external text" href="https://foldoc.org/Disk+controller">Disk+controller</a> at the <i><a href="Free_On-line_Dictionary_of_Computing" title="Free On-line Dictionary of Computing">Free On-line Dictionary of Computing</a></i> prior to 1 November 2008 and incorporated under the "relicensing" terms of the <a href="GNU_Free_Documentation_License" title="GNU Free Documentation License">GFDL</a>, version 1.3 or later.</span></span>

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</style><cite id="CITEREFJeppesenAllenAndersonPilsl2001" class="citation book cs1">Jeppesen, J.; Allen, W.; Anderson, S.; Pilsl, M. (2001). "Hard disk controller: The disk drive's brain and body". <a rel="nofollow" class="external text" href="https://ieeexplore.ieee.org/document/955038"><i>Proceedings 2001 IEEE International Conference on Computer Design: VLSI in Computers and Processors. ICCD 2001</i></a>. pp. <span class="nowrap">262–</span>267. <a href="Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1109%2FICCD.2001.955038">10.1109/ICCD.2001.955038</a>. <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <bdi>0-7695-1200-3</bdi>. <a href="S2CID_(identifier)" class="mw-redirect" title="S2CID (identifier)">S2CID</a> <a rel="nofollow" class="external text" href="https://api.semanticscholar.org/CorpusID:3084914">3084914</a><span class="reference-accessdate">. Retrieved <span class="nowrap">2023-10-18</span></span>.</cite></span>

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<ul><li><a href="Disk_array_controller" title="Disk array controller">Disk array controller</a></li>

<li><a href="Floppy-disk_controller" title="Floppy-disk controller">Floppy-disk controller</a></li>

<li><a href="Forensic_disk_controller" title="Forensic disk controller">Forensic disk controller</a></li></ul></div><div><div class="zim-footer">

This article is issued from <a class="external text" title="Last edited on 2025-04-07" href="https://en.wikipedia.org/wiki/?title=Disk_controller&oldid=1284486089">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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