Chapter 15

Question 1

What is SJF

Answer 1

Shortest job first is a scheduling algorithm in which the process with the smallest execution time is selected for execution next. Shortest job first can be either preemptive or non-preemptive.

Question 2

What are 2 versions of SJF

Answer 2

preemptive

non-preemptive

Question 3

What is preemptive and non-preemptive version of SJF

Answer 3

Tasks are usually assigned with priorities. At times it is necessary to run a certain task that has a higher priority before another task although it is running. Therefore, the running task is interrupted for some time and resumed later when the priority task has finished its execution. This is called preemptive scheduling.
Eg: Round robin

In non-preemptive scheduling, a running task is executed till completion. It cannot be interrupted.
Eg First In First Out

Question 4

Which is optimal non-preemptive scheduler

Answer 4

SJF is optimal scheduling algorithm and no scheduler gives such good performance.

Question 5

What is CPU burst time and CPU burst

Answer 5

While scheduling, each process gets to use the CPU for it’s slice. The slice that it gets, is called the CPU burst. In simple terms, the duration for which a process gets control of the CPU is the CPU burst time, and the concept of gaining control of the CPU is the CPU burst.

Question 6

Does Preemptive SJF also called Shortest remaining time first (SRTF)

Answer 6

Yes

Question 7

What is arrival time

Answer 7

Time at which the process arrives in the ready queue.

Question 8

What is exponential averaging

Answer 8

We can not know exactly the length of next CPU burst. We can only estimate the length of next CPU burst. It can only be done by using the length of previous CPU bursts using the exponential averaging.

Question 9

Does a process can have multiple CPU burst in its life time

Answer 9

Yes

Question 10

What is priority scheduling algorithm

Answer 10

Priority scheduling algorithm is used in a system when every process is assigned a priority. A priority number(integer) is associated with each process. Its a rule the smaller the number of priority has the highest priority.

Question 11

What is starvation problem

Answer 11

If there is high priority process use to come in system then low priority process will not get chance to proceed. It is called starvation problem.

Question 12

What is solution of starvation problem

Answer 12

Aging. As time progress increases the priority of task increases. Example of a shop keeper. Old customer waiting in queue will get high priority because he is waiting for sometime.

Question 13

What about task have 0 priority

Answer 13

It has highest priority