# CPU Scheduling

 Question 1
Consider four processes P, Q, R, and S scheduled on a CPU as per round robin algorithm with a time quantum of 4 units. The processes arrive in the order P, Q, R, S, all at time t = 0. There is exactly one context switch from S to Q, exactly one context switch from R to Q, and exactly two context switches from Q to R. There is no context switch from S to P. Switching to a ready process after the termination of another process is also considered a context switch. Which one of the following is NOT possible as CPU burst time (in time units) of these processes?
 A P = 4, Q = 10, R = 6, S = 2 B P = 2, Q = 9, R = 5, S = 1 C P = 4, Q = 12, R = 5, S = 4 D P = 3, Q = 7, R = 7, S = 3
GATE CSE 2022   Operating System
Question 1 Explanation:
 Question 2
Which of the following statement(s) is/are correct in the context of CPU scheduling?
[MSQ]
 A Turnaround time includes waiting time B The goal is to only maximize CPU utilization and minimize throughput C Round-robin policy can be used even when the CPU time required by each of the processes is not known apriori D Implementing preemptive scheduling needs hardware support
GATE CSE 2021 SET-2   Operating System
Question 2 Explanation:
 Question 3
Three processes arrive at time zero with CPU bursts of 16, 20 and 10 milliseconds. If the scheduler has prior knowledge about the length of the CPU bursts, the minimum achievable average waiting time for these three processes in a non-preemptive scheduler (rounded to nearest integer) is _____________ milliseconds.
 A 18.66 B 12 C 15 D 9
GATE CSE 2021 SET-1   Operating System
Question 3 Explanation:
 Question 4
Three CPU-bound tasks, with execution times of 15, 12 and 5 time units respectively arrive at times 0, t and 8, respectively. If the operating system implements a shortest remaining time first scheduling algorithm, what should be the value of t to have 4 context switches? Ignore the context switches at time 0 and at the end.
 A 0 < t < 3 B t=0 C t <= 3 D 3 < t < 8
ISRO CSE 2020   Operating System
Question 4 Explanation:
 Question 5
Which of the following algorithms defines time quantum?
 A shortest job scheduling algorithm B round robin scheduling algorithm C priority scheduling algorithm D multilevel queue scheduling algorithm
ISRO CSE 2020   Operating System
Question 5 Explanation:
 Question 6
Consider the following set of processes, assumed to have arrived at time 0. Consider the CPU scheduling algorithms Shortest Job First (SJF) and Round Robin (RR). For RR, assume that the processes are scheduled in the order $P_1,P_2,P_3,P_4$.

If the time quantum for RR is 4 ms, then the absolute value of the difference between the average turnaround times (in ms) of SJF and RR (round off to 2 decimal places is_______
 A 10.5 B 15.75 C 5.25 D 4.25
GATE CSE 2020   Operating System
Question 6 Explanation:
 Question 7
Consider the following four processes with arrival times (in milliseconds) and their length of CPU burst (in milliseconds) as shown below:
These processes are run on a single processor using preemptive Shortest Remaining Time First scheduling algorithm. If the average waiting time of the processes is 1 millisecond, then the value of Z is __________.
 A 1 B 2 C 3 D 4
GATE CSE 2019   Operating System
Question 7 Explanation:
 Question 8
Consider the set of processes with arrival time (in milliseconds). CPU burst time (in milliseconds), and priority (0 is the highest priority) shown below. None of the processes have I/O burst time.

The average waiting time (in milliseconds) of all the processes using preemptive priority scheduling algorithm is __________
 A 25 B 29 C 31 D 34
GATE CSE 2017 SET-2   Operating System
Question 8 Explanation:
 Question 9
Consider the following CPU processes with arrival times (in milliseconds) and length of CPU burst (in milliseconds) as given below:

If the pre-emptive shortest remaining time first scheduling algorithm is used to schedule the processes., then the average waiting time across all processes is ________ milliseconds.
 A 1 B 2 C 3 D 4
GATE CSE 2017 SET-1   Operating System
Question 9 Explanation:
 Question 10
In which one of the following page replacement policies, Belady's anomaly may occur?
 A FIFO B Optimal C LRU D MRU
ISRO CSE 2016   Operating System
Question 10 Explanation:
There are 10 questions to complete.

### 5 thoughts on “CPU Scheduling”

1. Q 20 has a wrong diagram…please update it