Consider the following memory-mapped register code: Figure from the original question paper What are the access sizes of the Figure from the original question paper and Figure from the original question paper registers, respectively?

(A) is 4-byte, and is 1-byte. (A figure from the original paper is missing from the source site.)

(B) Both registers are 1-byte. (A figure from the original paper is missing from the source site.)

(C) Both registers are 4-byte. (A figure from the original paper is missing from the source site.)

(D) is 1-byte, and is 4-byte. (A figure from the original paper is missing from the source site.)

What will be the output behavior of the following xv6 code snippet? Figure from the original question paper

(C) Both lines will be printed, but the order is non-deterministic. (A figure from the original paper is missing from the source site.)

(A) Only will be printed. (A figure from the original paper is missing from the source site.)

(B) Only will be printed. (A figure from the original paper is missing from the source site.)

(D) Parent always prints first, then child. (A figure from the original paper is missing from the source site.)

Consider the following code snippet for the syscall function in kernel/syscall.c (RISC-V xv6): Figure from the original question paper Why does xv6 store the system call number in the Figure from the original question paper register before invoking the kernel?

(C) To let the kernel identify which system call the user process is requesting.

(A) To store the return value of the system call.

(B) To indicate the number of bytes to be transferred.

(D) To store the stack pointer for the child process.

What could be the possible output of the following program? Figure from the original question paper

(B) Parent A: 6 Child A: 4 Child B: 12 Parent B: 14

(A) Child A: 4 Parent A: 6 Parent B: 14 Child B: 12

(C) Parent A: 6 Parent B: 8 Child A: 3 Child B: 12

(D) Child A: 2 Parent A: 6 Parent B: 14 Child B: 10

Consider the following processes in an xv6-like operating system:\ • Process P1 is ready to run and waiting in the run queue. • Process P2 is currently executing on the CPU. • Process P3 has called Figure from the original question paper waiting for an I/O event. • Process P4 has exited but its parent has not yet called Figure from the original question paper . Select all the correct statements about the states of the processes.

(A) Process P1 is in the RUNNABLE state.

(B) Process P2 is in the RUNNING state.

(C) Process P3 is in the SLEEPING state.

(D) Process P4 is in the ZOMBIE state.

(E) Process P3 is in the RUNNING state.

(F) Process P4 is in the RUNNABLE state.

January 2026 term · Operating Systems · BSCS4022

Operating Systems Quiz 1: 15 March 2026 (January 2026 term)

The IIT Madras BS Operating Systems (Operating Systems) Quiz 1 paper sat on 15 Mar 2026, in the January 2026 term: 18 questions for 50 marks in 120 minutes. Every question is below with its answer. Take it as a timed mock test to be marked, or read it through first.

Questions: 18
Marks: 50
Duration: 120 min
MCQ: 16
MSQ: 2

Take as mock test Practise with answers

Updated 25 Sept 2026

No negative marking.

Question 1

+3 marksOne correct option

If the memory map for a device starts from the offset 0x40002000 and has a size of 4096 bytes in a 32-bit addressing scheme, what will be the last address in the memory map?

A
0x40003000
B
0x40002EFF
C
0x40001FFF
D
0x40002FFF

Show answer

Correct answer

D
0x40002FFF

Question 1 on its own page

Question 2

+3 marksOne correct option

Consider the following memory-mapped register code:

What are the access sizes of the

and

registers, respectively?

A
is 4-byte, and is 1-byte.
(A figure from the original paper is missing from the source site.)
B
Both registers are 1-byte.
(A figure from the original paper is missing from the source site.)
C
Both registers are 4-byte.
(A figure from the original paper is missing from the source site.)
D
is 1-byte, and is 4-byte.
(A figure from the original paper is missing from the source site.)

Show answer

Correct answer

A
is 4-byte, and is 1-byte.
(A figure from the original paper is missing from the source site.)

Question 2 on its own page

Question 3

+3 marksOne correct option

What will be the output behavior of the following xv6 code snippet?

A
Only will be printed.
(A figure from the original paper is missing from the source site.)
B
Only will be printed.
(A figure from the original paper is missing from the source site.)
C
Both lines will be printed, but the order is non-deterministic.
(A figure from the original paper is missing from the source site.)
D
Parent always prints first, then child.
(A figure from the original paper is missing from the source site.)

Show answer

Correct answer

C
Both lines will be printed, but the order is non-deterministic.
(A figure from the original paper is missing from the source site.)

Question 3 on its own page

Question 4

+3 marksOne correct option

Which of the following correctly describes the sequence of steps when a new process is forked in xv6?
(i) Allocate a new proc structure. (ii) Copy the parent’s memory space to the child. (iii) Set up the trapframe for the child process. (iv) Add the child to the ready queue.

A
(i) → (iii) → (ii) → (iv)
B
(ii) → (i) → (iii) → (iv)
C
(i) → (ii) → (iii) → (iv)
D
(iii) → (i) → (ii) → (iv)

Show answer

Correct answer

C
(i) → (ii) → (iii) → (iv)

Question 4 on its own page

Question 5

+3 marksOne correct option

Consider image of the page table entry is given below and the code for kvminit in vm.c.

What will be the values of the first 5 bits (from the right) of the page table entry after the execution of

A
01110
B
00111
C
10110
D
10111

Show answer

Correct answer

B
00111

Question 5 on its own page

Question 6

+3 marksOne correct option

Consider the following code snippet for the syscall function in kernel/syscall.c (RISC-V xv6):

Why does xv6 store the system call number in the

A
To store the return value of the system call.
B
To indicate the number of bytes to be transferred.
C
To let the kernel identify which system call the user process is requesting.
D
To store the stack pointer for the child process.

Show answer

Correct answer

C
To let the kernel identify which system call the user process is requesting.

Question 6 on its own page

Question 7

+3 marksOne correct option

When a user types the command

in a Linux shell, which of the following sequences of system calls is most likely to occur for executing the command and then returning control to the shell?

A
exec-fork-wait
B
wait-exec-fork
C
fork-wait-exec
D
fork-exec-wait

Show answer

Correct answer

D
fork-exec-wait

Question 7 on its own page

Question 8

+4 marksOne correct option

A system has a virtual memory space of 8 GB and uses a single-level page table with 221 entries. What is the size of each page frame?

A
2 KB
B
4 KB
C
8 KB
D
16 KB

Show answer

Correct answer

B
4 KB

Question 8 on its own page

Question 9

+4 marksOne correct option

Consider a system with 128 MB of physical memory and a 32-bit virtual address space. Given a page size of 8 KB, what will be the maximum number of page frames that can be present in RAM?

A
212 frames
B
213 frames
C
214 frames
D
215 frames

Show answer

Correct answer

C
214 frames

Question 9 on its own page

Question 10

+4 marksOne correct option

What could be the possible output of the following program?

A
Child A: 4 Parent A: 6 Parent B: 14 Child B: 12
B
Parent A: 6 Child A: 4 Child B: 12 Parent B: 14
C
Parent A: 6 Parent B: 8 Child A: 3 Child B: 12
D
Child A: 2 Parent A: 6 Parent B: 14 Child B: 10

Show answer

Correct answer

B
Parent A: 6 Child A: 4 Child B: 12 Parent B: 14

Question 10 on its own page

Question 11

+2 marksOne correct option

In RISC-V, during system calls, which register stores the current program counter?

A
accumulator
B
exception program counter
C
mstatus
D
None of these

Show answer

Correct answer

B
exception program counter

Question 11 on its own page

Question 12

+2 marksOne correct option

Consider the given memory map.

The memory address 0x200003CD corresponds to ________

A
Mouse
B
Keyboard
C
Timers
D
Interrupt Controller
E
None of these

Show answer

Correct answer

A
Mouse

Question 12 on its own page

Question 13

+2 marksOne correct option

State True or False:
In xv6, after a user process calls fork(), both the parent and child processes have separate copies of the trapframe, so changes in one do not affect the other.

A
True
B
False

Show answer

Correct answer

A
True

Question 13 on its own page

Question 14

+2 marksOne correct option

In xv6, a running process can be preempted by the scheduler due to a timer interrupt. What is the resulting state transition of the process?

A
Running → Sleeping
B
Running → Zombie
C
Running → Runnable
D
State remains unchanged

Show answer

Correct answer

C
Running → Runnable

Question 14 on its own page

Question 15

+2 marksOne correct option

When a process invokes the exec system call, which components in the Process Control Block (PCB) remain unchanged?

A
Page table entries
B
Process identifier (PID)
C
The value of the program counter
D
File descriptor table and memory information

Show answer

Correct answer

B
Process identifier (PID)

Question 15 on its own pageAlso asked in Quiz 1 23 Feb 2025

Question 16

+2 marksOne correct option

Consider a process A that forks B, B forks C, and C forks D. Processes A and B keep running, but process C terminates before D finishes. Later, D also terminates. Which process is responsible for waiting for and reaping process D?

A
Process A
B
Process B
C
Process C
D
Process init

Show answer

Correct answer

D
Process init

Question 16 on its own page

Question 17

+2 marksOne or more correct options

Select the functions present in kernel/trampoline.S, and are responsible for switching from kernel pagetable to process pagetable and vice versa.

Select all that apply.

A
userret
B
usertrapret
C
trampoline
D
usertrap

Show answer

Correct answers

A
userret
C
trampoline

Question 17 on its own page

Question 18

+3 marksOne or more correct options

Consider the following processes in an xv6-like operating system:
• Process P1 is ready to run and waiting in the run queue. • Process P2 is currently executing on the CPU. • Process P3 has called

waiting for an I/O event. • Process P4 has exited but its parent has not yet called

. Select all the correct statements about the states of the processes.

Select all that apply.

A
Process P1 is in the RUNNABLE state.
B
Process P2 is in the RUNNING state.
C
Process P3 is in the SLEEPING state.
D
Process P4 is in the ZOMBIE state.
E
Process P3 is in the RUNNING state.
F
Process P4 is in the RUNNABLE state.

Show answer

Correct answers

A
Process P1 is in the RUNNABLE state.
B
Process P2 is in the RUNNING state.
C
Process P3 is in the SLEEPING state.
D
Process P4 is in the ZOMBIE state.

Question 18 on its own page