This is one way
to implement a RR scheme, but using priorities instead of position in a queue to choose the process to execute.
More commonly today, a system will implement multiple queues with different queue priorities, and then
schedule processes from the highest priority queue that has processes ready to run. The scheduling rule within
a particular queue may be RR or something else.
Starvation (withholding of CPU access) is always a possibility with any priority-based scheme. A system that
is at saturation (i.e., full capacity) will not be successful with any priority system. Imagine an airport commanded
to handle more air traffic than it can accommodate. One can give priority for landing to those short of fuel, but
if, in a given period of time, there are more airplanes to land than the airport can accommodate, very soon all
the aircraft in the sky will be short of fuel.
CHAP. 6] OPERATING SYSTEMS 115
Multilevel queues
A simple example of multiple queues with different priorities is a system where processes are classified as
interactive ???foreground??? processes and batch ???background??? processes. As long as there are foreground
processes ready to run, the system uses RR to share the CPU among the foreground processes.
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