The input/output units consists of the following two parts:
Basically, device controllers are the electronic components of input/output units.
Device controller can also called as adapter.
The mechanical component of the input/output unit is the device itself whereas the electronic component or device controller or adapter takes the form of a printed circuit card that can be inserted into an expansion slot.
Usually, the controller card has a connector on it, just to help in plugging the cable leading to the device controllers can handle many identical devices.