os cpu scheduling

For the processes listed in the following table, which of the following scheduling schemes will give the lowest average turnaround time?

• First Come First Serve

• Non-pre-emptive Shortest Job First

• Shortest Remaining Time

• Round Robin with Quantum value two

Consider an arbitrary set of CPU-bound processes with unequal CPU burst lengths submitted at the same time to a computer system. Which one of the following process scheduling algorithms would minimize the average waiting time in the ready queue?

• Shortest remaining time first

• Round-robin with time quantum less than the shortest CPU burst

• Uniform random

• Highest priority first with priority proportional to CPU burst length

Consider the following set of processes, with the arrival times and the CPU-burst times given in milliseconds

What is the average turnaround time for these processes with the pre-emptive shortest remaining processing time first (SRPT) algorithm?

• 5.50

• 5.75

• 6.00

• 6.25

Consider the following processes, with the arrival time and the length of the CPU burst given in milliseconds. The scheduling algorithm used is pre-emptive shortest remaining-time first.

The average turnaround time of these processes is (a)   milliseconds.

Consider the following CPU processes with arrival times (in milliseconds) and length of CPU bursts (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 (a)   milliseconds

An operating system uses shortest remaining time first scheduling algorithm for pre-emptive scheduling of processes. Consider the following set of processes with their arrival times and CPU burst times (in milliseconds)

The average waiting time (in milliseconds) of the processes is (a)   .

Consider three CPU intensive processes P1, P2, P3 which require 20,10 and 30 units of time, arrive at times 1,3 and 7 respectively. Suppose operating system is implementing Shortest Remaining Time first (pre-emptive scheduling) algorithm, then _____ context switches are required (suppose context switch at the beginning of Ready queue and at the end of Ready queue are not counted).

• 3

• 2

• 4

• 5

Consider three CPU-intensive processes, which require 10, 20 and 30 time units and arrive at times 0, 2 and 6, respectively. How many context switches are needed if the operating system implements a shortest remaining time first scheduling algorithm? Do not count the context switches at time zero and at the end.

• 1

• 2

• 3

• 4

Which of the following process scheduling algorithm may lead to starvation

• FIFO

• RR

• Shortest Job Next

• NONE

which of the following statements are true?

I. Shortest remaining time first scheduling may cause starvation

II. Preemptive scheduling may cause starvation

III. Round robin is better than FCFS in terms of response time

• I ONLY

• I AND IIIONLY

• II and III only

• I, II and III

Answer explanation

I) Shortest remaining time first scheduling is a pre-emptive version of shortest job scheduling. In SRTF, job with the shortest CPU burst will be scheduled first. Because of this process, It may cause starvation as shorter processes may keep coming and a long CPU burst process never gets CPU. II) Pre-emptive just means a process before completing its execution is stopped and other process can start execution. The stopped process can later come back and continue from where it was stopped. In pre-emptive scheduling, suppose process P1 is executing in CPU and after some time process P2 with high priority then P1 will arrive in ready queue then p1 is pre-empted and p2 will brought into CPU for execution. In this way if process which is arriving in ready queue is of higher priority then p1, then p1 is always pre-empted and it may possible that it suffer from starvation. III) round robin will give better response time then FCFS ,in FCFS when process is executing ,it executed up to its complete burst time, but in round robin it will execute up to time quantum. So Round Robin Scheduling improves response time as all processes get CPU after a specified time. So, I,II,III are true which is option (D). Reference: