As a controller (English for control unit or control unit ) electronic units of computer hardware are referred to that control certain operations. If these units only from an integrated circuit, they are usually called microcontrollers.
Controllers have the computer a variety of tasks: you take over the processing of interrupt requests (IRQs ), the keyboard input or control of accesses to the hard disk ( see, eg, ST506 ). In common parlance called controller components for hard disk access (eg IDE controller ) are nowadays but most host bus adapter. The controllers of hard disks in this sense have been housed since the proliferation of Integrated Drive Electronics (IDE ) in the 1980s in the hard disk itself; for SCSI hard drives was the already from the beginning.
In PC controller on plug-in cards or the motherboard of the computer itself are housed. Since the keyboard controller is one of the basic functions of the computer, this is always on the motherboard.
SCSI-3 " controller " (actually a host bus adapter ) with 50 - pin cable