Controller (computing)

In computing and especially in computer hardware, controller is a chip, an expansion card, or a stand-alone device that interfaces with a peripheral device. This may be a link between two parts of a computer (for example a memory controller that manages access to memory for the computer) or a controller on an external device that manages the operation of (and connection with) that device.

The term is sometimes used in the opposite sense to refer to a device by which the user controls the operation of the computer, as in game controller.

In desktop computers the controller may be a plug in board, a single integrated circuit on the motherboard, or an external device. In mainframes the controller is usually either a separate device attached to a channel or integrated into the peripheral.

Controller boards

Early desktop computers such as the IMSAI 8080 used expansion boards (or expansion cards) for all controllers, each handling a specific type of device. Examples of expansion board controllers are:

• Graphics controller or video display controller
• SCSI controller, more properly called SCSI host bus adapter
• Network interface controller (NIC)
• Parallel port controller

Controller chips

As chip densities improved controllers were implemented as single chips and often located on the motherboard. Examples are:

• Keyboard controller
• Programmable Interrupt Controller
• Northbridge (computing) – Intel memory controller chip
• Southbridge (computing) – Intel I/O controller chip
• Universal asynchronous receiver/transmitter (UART) communications controller chip
• Memory controller, logic which manages the flow of data in a computer system
• Peripheral DMA controller
• Floppy disk controller

Further integration enabled development of Super I/O chips — single chips that could control a variety of devices such as floppy disks, parallel ports, serial ports, keyboard, and mouse.

External controllers

• Disk controller, often integrated into modern disk drives.
• Disk array controller, also known as RAID controller, a type of storage controller
• Flash controller, or SSD controller, manages flash memory.
• Terminal Access Controller

Mainframe controllers

In IBM terminology a controller is "a device that decodes the [channel] command and effects the operation of the device."^[2]:p.5-1

In most mainframe systems a device-independent channel usually attaches to the CPU and a controller or control unit implements device-dependent logic for attaching specific devices to the channel. Some devices have integrated control units. Often a control unit can attach to multiple channels connected to a single or multiple systems. Some mainframe control units are:

• IBM 2821 Control Unit, used to attach card readers, punches and line printers to IBM System/360 and IBM System/370 computers
• IBM 270x and IBM 37xx, used for telecommunications
• IBM 3271, 3272, 3271, and 3174, used to attach terminals (display devices)

See also

• Control unit (disambiguation)
• Adapter (computing)
• Programmable logic controller
• Computer bus
• MIDI controller

References

External links

• Controller description at Webopedia, a computer term dictionary.