Operating system Process scheduling

Question

Which of the Algorithm gives long average waiting time?
(a) SJF (b) Round Robbin (c) FCFS (d) All of the above

Comments

Round robbin, due to every Process is rotating without completing.

---

Cannot be answered without more information,

For RR 

• Low average waiting time when job lengths vary widely 
• Poor average waiting time when jobs have similar lengths. Average waiting time is even worse than FCFS.

---

Source: https://www.cs.columbia.edu/~junfeng/10sp-w4118/lectures/l13-sched.pdf

Answer 1

Poor framing of ques ...where did u get ? No scenario is mentioned so difficult to give the correct answer

FCFS can have convoy effect.

SJF has minimum waiting time

RR have better when job lengths vary widely else they can have worse than FCFS when jobs length is same(source: Gavlin)

Answer 2

process number	burst_time
1	2
2	4
3	6
4	2

we can check all the option by taking a randomly example if any option holds true in general then it will hold for all the example.(arrival time=0)

(1) for SJF  AWT=3.5

(2) for FCFS AWT=5

(3) for ROUND ROBIN=5.5(tq=2 unit)

so for round robin AWT is large.