Disk controller

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Seagate ST11R, an 8-bit ISA RLL hard disk controller produced in 1990. Seagate ST11R.jpg
Seagate ST11R, an 8-bit ISA RLL hard disk controller produced in 1990.

A disk controller is a controller 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. [1] [2]

Contents

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 created a proprietary storage algorithm that could double the disk storage. Shugart Associates Systems 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 PATA (IDE) and Serial ATA for home use. High-end disks use Parallel SCSI, Fibre Channel or Serial Attached SCSI.

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 hardware RAID to be formed. Sometimes it may be even physically integrated with an HBA.

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<span class="mw-page-title-main">Bus (computing)</span> System that transfers data between components within a computer

In computer architecture, a bus is a communication system that transfers data between components inside a computer, or between computers. This expression covers all related hardware components and software, including communication protocols.

<span class="mw-page-title-main">Industry Standard Architecture</span> Internal expansion bus in early PC compatibles

Industry Standard Architecture (ISA) is the 16-bit internal bus of IBM PC/AT and similar computers based on the Intel 80286 and its immediate successors during the 1980s. The bus was (largely) backward compatible with the 8-bit bus of the 8088-based IBM PC, including the IBM PC/XT as well as IBM PC compatibles.

<span class="mw-page-title-main">Motherboard</span> Main printed circuit board (PCB) used for a computing device

A motherboard is the main printed circuit board (PCB) in general-purpose computers and other expandable systems. It holds and allows communication between many of the crucial electronic components of a system, such as the central processing unit (CPU) and memory, and provides connectors for other peripherals. Unlike a backplane, a motherboard usually contains significant sub-systems, such as the central processor, the chipset's input/output and memory controllers, interface connectors, and other components integrated for general use.

<span class="mw-page-title-main">SCSI</span> Set of computer and peripheral connection standards

Small Computer System Interface is a set of standards for physically connecting and transferring data between computers and peripheral devices, best known for its use with storage devices such as hard disk drives. SCSI was introduced in the 1980s and has seen widespread use on servers and high-end workstations, with new SCSI standards being published as recently as SAS-4 in 2017.

Internet Small Computer Systems Interface or iSCSI is an Internet Protocol-based storage networking standard for linking data storage facilities. iSCSI provides block-level access to storage devices by carrying SCSI commands over a TCP/IP network. iSCSI facilitates data transfers over intranets and to manage storage over long distances. It can be used to transmit data over local area networks (LANs), wide area networks (WANs), or the Internet and can enable location-independent data storage and retrieval.

<span class="mw-page-title-main">ST506/ST412</span>

The ST-506 and ST-412 were early hard disk drive products introduced by Seagate in 1980 and 1981 respectively, that later became construed as hard disk drive interfaces: the ST-506 disk interface and the ST-412 disk interface. Compared to the ST-506 precursor, the ST-412 implemented a refinement to the seek speed, and increased the drive capacity from 5 MB to 10 MB, but was otherwise highly similar.

<span class="mw-page-title-main">SATA</span> Computer bus interface for storage devices

SATA is a computer bus interface that connects host bus adapters to mass storage devices such as hard disk drives, optical drives, and solid-state drives. Serial ATA succeeded the earlier Parallel ATA (PATA) standard to become the predominant interface for storage devices.

<span class="mw-page-title-main">Host adapter</span> Computer hardware device

In computer hardware a host controller, host adapter or host bus adapter (HBA) connects a computer system bus which acts as the host system to other network and storage devices. The terms are primarily used to refer to devices for connecting SCSI, SAS, NVMe, Fibre Channel and SATA devices. Devices for connecting to FireWire, USB and other devices may also be called host controllers or host adapters.

A disk array controller is a device that manages the physical disk drives and presents them to the computer as logical units. It almost always implements hardware RAID, thus it is sometimes referred to as RAID controller. It also often provides additional disk cache.

<span class="mw-page-title-main">QEMU</span> Free virtualization and emulation software

QEMU is a free and open-source emulator. It emulates a computer's processor through dynamic binary translation and provides a set of different hardware and device models for the machine, enabling it to run a variety of guest operating systems. It can interoperate with Kernel-based Virtual Machine (KVM) to run virtual machines at near-native speed. QEMU can also do emulation for user-level processes, allowing applications compiled for one processor architecture to run on another.

<span class="mw-page-title-main">Floppy-disk controller</span> Circuitry that controls reading from and writing to a computers floppy disk drive

A floppy-disk controller (FDC) is a hardware component that directs and controls reading from and writing to a computer's floppy disk drive (FDD). It has evolved from a discrete set of components on one or more circuit boards to a special-purpose integrated circuit or a component thereof. An FDC is responsible for reading data presented from the host computer and converting it to the drive's on-disk format using one of a number of encoding schemes, like FM encoding or MFM encoding, and reading those formats and returning it to its original binary values.

<span class="mw-page-title-main">Commodore 64 peripherals</span>

The Commodore 64 home computer used various external peripherals. Due to the backwards compatibility of the Commodore 128, most peripherals would also work on that system. There is also some compatibility with the VIC-20 and Commodore PET.

A SCSI connector is used to connect computer parts that communicate with each other via the SCSI standard. Generally, two connectors, designated male and female, plug together to form a connection which allows two components, such as a computer and a disk drive, to communicate with each other. SCSI connectors can be electrical connectors or optical connectors. There have been a large variety of SCSI connectors in use at one time or another in the computer industry. Twenty-five years of evolution and three major revisions of the standards resulted in requirements for Parallel SCSI connectors that could handle an 8, 16 or 32 bit wide bus running at 5, 10 or 20 megatransfer/s, with conventional or differential signaling. Serial SCSI added another three transport types, each with one or more connector types. Manufacturers have frequently chosen connectors based on factors of size, cost, or convenience at the expense of compatibility.

Tagged Command Queuing (TCQ) is a technology built into certain ATA and SCSI hard drives. It allows the operating system to send multiple read and write requests to a hard drive. ATA TCQ is not identical in function to the more efficient Native Command Queuing (NCQ) used by SATA drives. SCSI TCQ does not suffer from the same limitations as ATA TCQ.

<span class="mw-page-title-main">Adapter (computing)</span> Adapter used in computing

An adapter in regard to computing can be either a hardware component (device) or software that allows two or more incompatible devices to be linked together for the purpose of transmitting and receiving data. Given an input, an adapter alters it in order to provide a compatible connection between the components of a system. Both software and hardware adapters are used in many different devices such as mobile phones, personal computers, servers and telecommunications networks for a wide range of purposes. Some adapters are built into devices, while the others can be installed on a computer's motherboard or connected as external devices.

<span class="mw-page-title-main">Storage area network</span> Network which provides access to consolidated, block-level data storage

A storage area network (SAN) or storage network is a computer network which provides access to consolidated, block-level data storage. SANs are primarily used to access data storage devices, such as disk arrays and tape libraries from servers so that the devices appear to the operating system as direct-attached storage. A SAN typically is a dedicated network of storage devices not accessible through the local area network (LAN).

In addition to the Amiga chipsets, various specially designed chips have been used in Commodore Amiga computers that do not belong to the 'Amiga chipset' in a tight sense.

This glossary of computer hardware terms is a list of definitions of terms and concepts related to computer hardware, i.e. the physical and structural components of computers, architectural issues, and peripheral devices.

Hard disk drives are accessed over one of a number of bus types, including parallel ATA, Serial ATA (SATA), SCSI, Serial Attached SCSI (SAS), and Fibre Channel. Bridge circuitry is sometimes used to connect hard disk drives to buses with which they cannot communicate natively, such as IEEE 1394, USB, SCSI, NVMe and Thunderbolt.

References

  1. This article is based on material taken from Disk+controller at the Free On-line Dictionary of Computing prior to 1 November 2008 and incorporated under the "relicensing" terms of the GFDL, version 1.3 or later.
  2. Jeppesen, J.; Allen, W.; Anderson, S.; Pilsl, M. (2001). "Hard disk controller: The disk drive's brain and body". Proceedings 2001 IEEE International Conference on Computer Design: VLSI in Computers and Processors. ICCD 2001. pp. 262–267. doi:10.1109/ICCD.2001.955038. ISBN   0-7695-1200-3. S2CID   3084914 . Retrieved 2023-10-18.

See also