The IIT Madras BS Operating Systems (Operating Systems) End Term paper sat on 10 May 2026, in the January 2026 term, set 1: 20 questions for 50 marks in 180 minutes. Every question is below with its answer. Take it as a timed mock test to be marked, or read it through first.
Consider the below plots representing the order in which the requests are serviced by different disk scheduling algorithms.
Match the above plots with the corresponding disk scheduling algorithm.
(1) - C-SCAN, (2) - FCFS, (3) - SCAN, (4) - C-LOOK
(1) - C-LOOK, (2) - FCFS, (3) - SCAN, (4) - C-SCAN
(1) - SCAN, (2) - C-SCAN, (3) - C-LOOK, (4) - FCFS
(1) - C-LOOK, (2) - C-SCAN, (3) - FCFS, (4) - SCAN
Correct answer
(1) - C-SCAN, (2) - FCFS, (3) - SCAN, (4) - C-LOOK
Consider the following program. Assume execlp succeeds.
Which output order is guaranteed?
parent done appears before hello
hello appears before parent done
Only parent done appears
The order is non-deterministic
Correct answer
hello appears before parent done
Consider the following resource-allocation situation.
• Process P1 holds resource R1 and waits for R2. • Process P2 holds resource R2 and waits for R3. • Process P3 holds resource R3 and waits for R1. • None of the processes releases its currently held resource until it acquires the requested one.
Which deadlock condition is most directly exhibited by the waiting pattern above?
Mutual exclusion
Preemption
Circular wait
Time sharing
Correct answer
Circular wait
If the memory map for a device starts at address 0x40001000 and has a size of 8192 bytes, what is the last valid address in the memory map?
0x40002000
0x40002FFE
0x40002FFF
0x40003000
Correct answer
0x40002FFF
Consider that the following commands are executed in a shell with root (/) as the current directory.
What is the absolute path of the file report.txt?
/data/processed/report.txt
/data/raw/monthly/report.txt
/data/processed/monthly/report.txt
/monthly/report.txt
Correct answer
/data/processed/monthly/report.txt
In xv6 on RISC-V, which register contains the system call number when the user process traps into the kernel?
a0
a7
sp
sepc
Correct answer
a7
When a shell executes a command and then waits for it to finish before printing the next prompt, which sequence of system calls is most likely used?
exec → fork → wait
wait → fork → exec
fork → wait → exec
fork → exec → wait
Correct answer
fork → exec → wait
In a 64-bit RISC-V system, the scause register stores trap information. What will be the value of scause for an Environment call from U-mode?
0x0000000000000008
0x8000000000000008
0x0000000000000009
0x8000000000000009
Correct answer
0x0000000000000008
What is the major disadvantage of the First-Come, First-Served (FCFS) CPU scheduling algorithm?
Starvation of long processes
Convoy effect due to long CPU-bound processes
It always requires page replacement
It cannot be implemented without virtual memory
Correct answer
Convoy effect due to long CPU-bound processes
When a process successfully invokes the exec system call, which of the following definitely remains unchanged?
Program counter value
Address space contents
Process identifier (PID)
User stack contents
Correct answer
Process identifier (PID)
Consider the code segment (for xv6) given below.
What are the base address and the end address of the count reg?
The base address is 0xD200401A, and the end address is 0xD200401C.
The base address is 0xD2004018, and the end address is 0xD2004019.
The base address is 0xD200401A, and the end address is 0xD200401B.
The base address is 0xD2004026, and the end address is 0xD2004027.
Correct answer
The base address is 0xD200401A, and the end address is 0xD200401B.
Consider the following code snippet
Which of the following statements is correct?
The program creates three threads, each printing "Operating Systems" 50 times, and "Done" is printed only after all thread outputs are completed.
The program creates three threads, each printing "Operating Systems" 50 times, but "Done" may appear before some thread outputs.
The program creates one thread at a time due to pthread join, resulting in sequential execution.
The program prints "Operating Systems" exactly 50 times in total and then prints "Done".
Correct answer
The program creates three threads, each printing "Operating Systems" 50 times, and "Done" is printed only after all thread outputs are completed.
Consider the following processes in an xv6-like operating system:
• Process P1 is waiting in the ready queue. • Process P2 is currently executing on the CPU. • Process P3 is blocked waiting for disk I/O. • Process P4 has terminated, but its parent has not yet called wait().
P1 is in the RUNNABLE state.
P2 is in the RUNNING state.
P3 is in the SLEEPING state.
P4 is in the ZOMBIE state.
P3 is in the RUNNABLE state.
P4 is in the RUNNING state.
Correct answers
P1 is in the RUNNABLE state.
P2 is in the RUNNING state.
P3 is in the SLEEPING state.
P4 is in the ZOMBIE state.
Assume that context switches can occur at any time during execution. The variable counter is shared between two concurrent threads/processes. Initial value: counter = 100
Program A R1 = counter R1 = R1 + 30 counter = R1
Program B R2 = counter R2 = R2 - 20 counter = R2
Which of the following can be the possible final values of counter?
80
110
130
90
100
120
Correct answers
80
110
130
Choose all correct statements regarding compiling and linking multiple C source files using gcc.
gcc file1.c file2.c -o output produces an executable named output.
gcc -c file1.c file2.c produces file1.o and file2.o.
gcc file1.o file2.o -o output links the object files into an executable named output.
gcc -c file1.c file2.c -o output produces an executable named output.
gcc file1.o file2.o -c -o output produces an executable named output.
Correct answers
gcc file1.c file2.c -o output produces an executable named output.
gcc -c file1.c file2.c produces file1.o and file2.o.
gcc file1.o file2.o -o output links the object files into an executable named output.
A system has 256 MiB of physical memory and uses a page size of 4 KiB. How many page frames are present in RAM?
Assume 1 MiB = 220 bytes and 1 KiB = 210 bytes.
Correct answer: 65536
Consider the following processes, all arriving at time 0 and entering the ready queue in the order shown below.
If the CPU scheduling policy is Round Robin with time quantum 2, what is the average response time?
Correct answer: 3
Consider the following processes scheduled using FCFS.
What is the average waiting time?
Correct answer: 3.5
Consider the following processes scheduled using non-preemptive SJF.
What is the average response time?
Correct answer: 4
A system uses a 32-bit virtual address space with a page size of 4 KiB and a single-level page table. How many entries are required in the page table?
Assume 1 KiB = 210 bytes
Correct answer: 1048576
