Page 91 - DCAP403_Operating System

Operating System

Notes Throughput N/A low for small high high high N/A
quantum
Response May be high good for short good for short good good N/A
Time processes processes
Overhead minimal low Can be high can be high can be high can be high
Effect on
Processes
Starvation No No Possible Possible No Possible
w = time spent in the system so far, waiting and executing
e = time spent in execution so far.
s = total service time required by the process, including e.

Task “Priority scheduling can be preemptive or non-preemptive.” Discuss.

5.4 Operating Systems and Scheduling Types

1. Solaris 2 uses priority-based process scheduling.

2. Windows 2000 uses a priority-based preemptive scheduling algorithm.
3. Linux provides two separate process-scheduling algorithms: one is designed for time-
sharing processes for fair preemptive scheduling among multiple processes; the other
designed for real-time tasks:
(a) For processes in the time-sharing class Linux uses a prioritized credit-based
algorithm
(b) Real-time scheduling: Linux implements two real-time scheduling classes namely

FCFS (First come first serve) and RR (Round Robin)
5.5 Types of Scheduling

In many multitasking systems the processor scheduling subsystem operates on three levels,
differentiated by the time scale at which they perform their operations. In this sense differentiate
among:
1. Long term scheduling: which determines which programs are admitted to the system for
execution and when, and which ones should be exited.

2. Medium term scheduling: which determines when processes are to be suspended and
resumed;
3. Short term scheduling (or dispatching): which determines which of the ready processes can
have CPU resources, and for how long.

5.5.1 Long-term Scheduling

Long term scheduling obviously controls the degree of multiprogramming in multitasking
systems, following certain policies to decide whether the system can honour a new job submission
or, if more than one job is submitted, which of them should be selected. The need for some form
of compromise between degree of multiprogramming and throughput seems evident, especially
when one considers interactive systems. The higher the number of processes, in fact, the smaller

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