GATE CSE Operating System PYQs & Answers — Page 2

Questions 11–20 of 65. Imported answers require independent review unless marked reviewed.

Suppose in a multiprogramming environment, the following C program segment is executed. A process goes into I/O queue whenever an I/O related operation is performed. Assume that there will always be a context switch whenever a process requests for an I/O, and also whenever the process returns from an I/O. The number of times the process will enter the ready queue during its life time (not counting the time the process enters the ready queue when it is run initially) is ______. (Answer in integer)

int main()

{

int x=0,i=0;

scanf("%d",&x);

for(i=0; i<20; i++)

{

x = x+20;

printf("%d\n",x);

}

return 0;

}

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A computer has two processors,

and

. Four processes

with CPU bursts of 20, 16, 25, and 10 milliseconds, respectively, arrive at the same time and these are the only processes in the system. The scheduler uses non-preemptive priority scheduling, with priorities decided as follows:

•

uses priority of execution for the processes as,

, i.e.,

and

have highest and lowest priorities, respectively. •

uses priority of execution for the processes as,

, i.e.,

and

have highest and lowest priorities, respectively.

A process

is scheduled to a processor

, if the processor is free and no other process

is waiting with higher priority. At any given point of time, a process can be allocated to any one of the free processors without violating the execution priority rules. Ignore the context switch time. What will be the average waiting time of the processes in milliseconds?

Your answerChoose one option.

9.00

8.75

6.50

7.50

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Consider a demand paging system with three frames, and the following page reference string: 1 2 3 4 5 4 1 6 4 5 1 3 2. The contents of the frames are as follows initially and after each reference (from left to right):

initial	after
-	1* 2* 3* 4* 5* 4 1 6* 4 5 1* 3* 2*
-	1 1 1 1 1 1 1 6 6 6 6 6 2
-	- 2 2 4 4 4 4 4 4 4 4 1 1
-	- - 3 3 5 5 5 5 5 5 5 3 3

The *-marked references cause page replacements.

Which one or more of the following could be the page replacement policy/policies in use?

Your answerSelect all correct options. You can choose more than one.

Least Recently Used page replacement policy

Least Frequently Used page replacement policy

Most Frequently Used page replacement policy

Optimal page replacement policy

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consists of all active processes in an operating system.

consists of single instances of distinct types of resources in the system.

The resource allocation graph has the following assignment and claim edges.

Assignment edges:

(the assignment edge

means resource

is assigned to process

, and so on for others)

Claim edges:

(the claim edge

means process

is waiting for resource

, and so on for others)

Which of the following statement(s) is/are CORRECT?

Your answerSelect all correct options. You can choose more than one.

Aborting

makes the system deadlock free.

Aborting

makes the system deadlock free.

Aborting

makes the system deadlock free.

Aborting

and

makes the system deadlock free.

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A disk of size 512M bytes is divided into blocks of 64K bytes. A file is stored in the disk using linked allocation. In linked allocation, each data block reserves 4 bytes to store the pointer to the next data block. The link part of the last data block contains a NULL pointer (also of 4 bytes). Suppose a file of 1M bytes needs to be stored in the disk. Assume, 1K =

and 1M =

. The amount of space in bytes that will be wasted due to internal fragmentation is _____. (Answer in integer)

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In optimal page replacement algorithm, information about all future page references is available to the operating system (OS). A modification of the optimal page replacement algorithm is as follows:

The OS correctly predicts only up to next 4 page references (including the current page) at the time of allocating a frame to a page.

A process accesses the pages in the following order of page numbers:

1, 3, 2, 4, 2, 3, 1, 2, 4, 3, 1, 4.

If the system has three memory frames that are initially empty, the number of page faults that will occur during execution of the process is ______. (Answer in integer)

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Which of the following statements about threads is/are TRUE?

Your answerSelect all correct options. You can choose more than one.

Threads can only be implemented in kernel space

Each thread has its own file descriptor table for open files

All the threads belonging to a process share a common stack

Threads belonging to a process are by default not protected from each other

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Which of the following process state transitions is/are NOT possible?

Your answerSelect all correct options. You can choose more than one.

Running to Ready

Wait to Running

Ready to Waiting

Running to Terminated

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Consider a process P running on a CPU. Which one or more of the following events will always trigger a context switch by the OS that results in process P moving to a non-running state (e.g., ready, blocked)?

Your answerSelect all correct options. You can choose more than one.

P makes a blocking system call to read a block of data from the disk

P tries to access a page that is in the swap space, triggering a page fault

An interrupt is raised by the disk to deliver data requested by some other process

A timer interrupt is raised by the hardware

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Consider a single processor system with four processes A, B, C, and D, represented as given below, where for each process the first value is its arrival time, and the second value is its CPU burst time.

A (0, 10), B (2, 6), C (4, 3), and D (6, 7).

Which one of the following options gives the average waiting times when preemptive Shortest Remaining Time First (SRTF) and Non-Preemptive Shortest Job First (NP-SJF) CPU scheduling algorithms are applied to the processes?

Your answerChoose one option.

SRTF = 6, NP-SJF = 7

SRTF = 6, NP-SJF = 7.5

SRTF = 7, NP-SJF = 7.5

SRTF = 7, NP-SJF = 8.5

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GATE CSE Operating System PYQs

Question 29

Question 38

Question 47

Question 48

Question 51

Question 54

Question 24

Question 25

Question 25

Question 37