The Amiga system devices are software engines that provide access to the
Amiga hardware.   Through these devices, a programmer can operate a modem,
spin a disk drive motor, time an event, and blast a trumpet sound in
stereo.  Yet, for all that variety, the programmer uses each device in the
same manner.

 what is a device?     using a device            using an exec device 
 accessing a device    devices with functions    function reference