Editing Disk controller

{{Short description|Controller for disk storage, usually integrated into the drive}}
{{confused|Host adapter}}
{{More citations needed|date=October 2023}}
[[File:Seagate ST11R.jpg|thumb|Seagate ST11R, an 8-bit [[ISA card|ISA]] [[RLL encoding|RLL]] hard disk controller produced in 1990.]]

A '''disk controller''' is a controller [[Electronic circuit|circuit]] that enables a [[CPU]] to communicate with a [[hard disk]], [[floppy disk]] or other kind of [[disk drive]]. It also provides an interface between the disk drive and the bus connecting it to the rest of the system.<ref>{{FOLDOC|Disk+controller}}</ref><ref>{{Cite book |url=https://ieeexplore.ieee.org/document/955038 |access-date=2023-10-18 |date=2001 |doi=10.1109/ICCD.2001.955038 |s2cid=3084914 |language=en-US |last1=Jeppesen |first1=J. |last2=Allen |first2=W. |last3=Anderson |first3=S. |last4=Pilsl |first4=M. |title=Proceedings 2001 IEEE International Conference on Computer Design: VLSI in Computers and Processors. ICCD 2001 |chapter=Hard disk controller: The disk drive's brain and body |pages=262–267 |isbn=0-7695-1200-3 }}</ref>

Early disk controllers were identified by their storage methods and data encoding.  They were typically implemented on a separate controller card. [[Modified frequency modulation]] (MFM) controllers were the most common type in small computers, used for both floppy disk and hard disk drives. [[Run length limited]] (RLL) controllers used data compression to increase storage capacity by about 50%.  [[Priam Corporation | Priam]] created a proprietary storage algorithm that could double the disk storage.  [[Shugart Associates]] Systems Interface ([[Shugart Associates System Interface|SASI]]) was a predecessor to [[SCSI]]. 

Modern disk controllers are integrated into the disk drive as peripheral controllers. For example, ''SCSI disks'' 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.

These integrated peripheral controllers communicate with a [[host adapter]] in the host system over a standardized, high-level [[storage bus]] interface. The most common types of interfaces provided nowadays by host controllers are [[Parallel ATA|PATA (IDE)]] and [[Serial ATA]] for home use. High-end disks use [[Parallel SCSI]], [[Fibre Channel]] or [[Serial Attached SCSI]]. The peripheral controller integrated on [[Parallel ATA|PATA (IDE)]], [[Serial ATA]], [[Parallel SCSI]] or [[Serial Attached SCSI]] hard disk is usually a [[microcontroller]] or an [[ASIC]].

Disk controllers can also control the timing of access to [[flash memory]], which is not mechanical in nature (i.e. no spinning disk).

==Disk controller versus host adapter==
The component that allows a ''computer'' to talk to a peripheral bus is a [[host adapter]] or host bus adapter (HBA, e.g. [[Advanced Host Controller Interface]] or AHDC). A disk controller allows a ''disk'' to talk to the same bus. Signals read by a [[disk read-and-write head]] 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 [[motherboard]]'s bus, and then read by the [[CPU]] into the memory (RAM).

Sometimes there may be yet another controller between a host adapter and a disk controller - a [[disk array controller]] that allows [[RAID#Hardware-based|hardware RAID]] to be formed. Sometimes it may be even physically integrated with an HBA.

== References ==
<references />

==See also==
* [[Disk array controller]]
* [[Floppy-disk controller]]
* [[Forensic disk controller]]

[[Category:Computer data storage]]
[[Category:Integrated circuits]]

[[fr:Disque dur#Contrôleur de disque]]