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Disk controller
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<p>A disk controller is a controller <a href="/facts/Electronic_circuit/IRfQ6Cc2">circuit</a> that enables a <a href="/facts/CPU/Jxp1bqMV">CPU</a> to communicate with a <a href="/facts/Hard_disk/kekLSGSE">hard disk</a>, <a href="/facts/Floppy_disk/rShxfuxa">floppy disk</a> or other kind of <a href="/facts/Disk_drive/hnsXRb5X">disk drive</a>. It also provides an interface between the disk drive and the bus connecting it to the rest of the system. </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="/facts/Modified_frequency_modulation/XLIItN1f">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="/facts/Run_length_limited/WkGWpAGR">Run length limited</a> (RLL) controllers used data compression to increase storage capacity by about 50%. <a href="/facts/Priam_Corporation/rzteHkJW"> Priam</a> created a proprietary storage algorithm that could double the disk storage. <a href="/facts/Shugart_Associates/WIJh0Y0A">Shugart Associates</a> Systems Interface (<a href="/facts/Shugart_Associates_System_Interface/pxXulrBr">SASI</a>) was a predecessor to <a href="/facts/SCSI/pxXulrBr">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="/facts/Host_adapter/nQbbDHF2">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="/facts/Parallel_ATA/QPchqXH8">PATA (IDE)</a> and <a href="/facts/Serial_ATA/dW8yAMm8">Serial ATA</a> for home use. High-end disks use <a href="/facts/Parallel_SCSI/7dVrf7Lc">Parallel SCSI</a>, <a href="/facts/Fibre_Channel/C7C0yreb">Fibre Channel</a> or <a href="/facts/Serial_Attached_SCSI/ekU6NmqQ">Serial Attached SCSI</a>. The peripheral controller integrated on <a href="/facts/Parallel_ATA/QPchqXH8">PATA (IDE)</a>, <a href="/facts/Serial_ATA/dW8yAMm8">Serial ATA</a>, <a href="/facts/Parallel_SCSI/7dVrf7Lc">Parallel SCSI</a> or <a href="/facts/Serial_Attached_SCSI/ekU6NmqQ">Serial Attached SCSI</a> hard disk is usually a <a href="/facts/Microcontroller/MKrnAhnm">microcontroller</a> or an <a href="/facts/ASIC/YGUXpX50">ASIC</a>. </p><p>Disk controllers can also control the timing of access to <a href="/facts/Flash_memory/Cn8JsStx">flash memory</a> which is not mechanical in nature (i.e. no spinning disk). </p>