priority scheduling

    Processes scheduling in which the
   scheduler selects tasks to run based on their priority as
   opposed to, say, a simple round-robin.

   Priorities may be static or dynamic.  Static priorities are
   assigned at the time of creation, while dynamic priorities are
   based on the processes' behaviour while in the system.  For
   example, the scheduler may favour I/O-intensive tasks so
   that expensive requests can be issued as early as possible.

   A danger of priority scheduling is starvation, in which
   processes with lower priorities are not given the opportunity
   to run.  In order to avoid starvation, in preemptive
   scheduling, the priority of a process is gradually reduced
   while it is running.  Eventually, the priority of the running
   process will no longer be the highest, and the next process
   will start running.  This method is called aging.