States and Data Invariant
The state of the spooler is represented by the four
components Queues, OutputDevices, Limits, and Sizes.
The data invariant has five components:
Each output device is associated with an upper limit
of print lines
Each output device is associated with a possibly
nonempty queue of files awaiting printing
Each file is associated with a size
Each queue associated with an output device contains
files that have a size less than the upper limit of the
output device
There will be no more than MaxDevs output devices
administered by the spooler