Controller (computing)

In computing and especially in computer hardware, a 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

Video display controller expansion board

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:

Controller chips

Intel C8251 Universal Synchronous/Asynchronous Receiver/Transmitter (USART) chip

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

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

A disassembled and labeled disk drive showing controller integrated into the drive.

Mainframe controllers

IBM 1311 Disk Drives. Model 3 (on right) contains an integrated controller for itself and up to 3 Model 2s (on left).[1]:p.2

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 to a controller or control unit which implements device-dependent logic for attaching specific devices. The functions performed by the control unit are similar to the functions performed by a device driver program on smaller systems. Some devices have integrated control units, which are logically discrete but are included with the device rather than requiring a separate box. Often a control unit can attach to multiple channels connected to a single or multiple systems. Some mainframe control units are:

See also

References

External links

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