of waiting processes. The CPU is a server with its ready
queue, as is the I/O system with its device queues.
Knowing arrival rates and service rates, we can compute
utilization, average queue length, average wait, and so on.
This area is called queueing-network analysis.
2.4.3 Simulations: This is the imitation of the operation
of a real-world process or system over time. Whether done
by hand or on a computer, simulation involves the
generation of an artificial history of a system and the
observation of that artificial history to draw inferences
concerning the operating characteristics of the real system
(Bank et al 2005). To get a more accurate evaluation of
scheduling algorithms, we can use simulations
(Silberschatz et al 2002).
2.4.4 Implementation: This approach puts the actual
algorithm in the real system for evaluation under real
operating conditions. The major difficult y with this
approach is the high cost. The expense is incurred not only
in coding the algorithm and modifying the operating
system to support it (along with its required data
structures) but also in the reaction of the users to a
constantly changing operating system. Another difficultly
is the environment in which the algorithm is used will
change. The environment will change not only in the usual
way, as new programs are written and the types of
problems change, but also as a result of the performance of
the scheduler. If short processed are given priority, then
users may break larger processes are given priority, then
users may break larger processes into sets of smaller
processes. If interactive processes are given priority over
non interactive processes, then users may switch to
interactive use.