All connected Volume Sets (CPUs) make use of a single, replicable, Device
Each CPU has several ports to which devices may be connected. The port
number is the $I value. Most physical devices are thus connected to one
CPU via one $I. When using the device, however, different specifications
may be used for output. It is the device name which distinguishes the
specifications such as open and close execute or use parameters. Each
entry in the Device File, then, uniquely identifies a set of instructions
to send to a $I location on a particular CPU.
File. All information concerning a particular device is stored in just one
place which facilitates device management.
One way to demonstrate the structure of the Device File is to experiment
with [DEVICE LOOKUP] by using an option like Device Edit. Notice the
fields 'Name', 'Device $I', and 'Volume Set(CPU)'. Together, these three
attributes characterize an entry in the Device File.