A single application can be broken up into several parts, each one associated with a separate process. This division of labour often makes the program easier to write. As an example consider a screen manager that displays several windows simultaneously and accepts user input from each window. In a sequential processing system, exactly one process is assigned to this application. It would maintain a ``context block'' for each window and ``switch'' among these blocks based on user input. The program for this process would look as follows:
initialize all windows.
{\bf loop}
wait for user input
determine the window to which it applies
load state of window
service input
save state
{\bf end loop}
In a multiprocess system,
a process could be associated with each window.
The state of a window is stored in the variables of its process,
and the operating system is responsible for saving and restoring this state
and switching among the processes.
Moreover,
it can support urgent windows (``abort missile launch'')
by giving higher priority to processes that manage them.
Thus each process is concerned only with servicing input,
and not with saving and restoring state.