Practise 39 System Software and Operating System questions asked in UGC NET Computer Science from 2020–2025. Questions cover System software, Process management, Threads, Classical synchronisation problems, Deadlock and Memory management. Every question is shown with its options and the correct answer, free to read.
Practise System Software and Operating System as timed sets
Focused 10-question sets with instant scoring, explanations, and weak-area analysis.
Ordered newest exam first. Each question links back to the full paper it came from.
Match List-I with List-II.
| List-I | List-II |
|---|---|
| A. RAID 1 B. RAID 2 C. RAID 3 D. RAID 4 | I. bit-interleaved parity II. disk mirroring III. block-interleaved parity IV. ECC organisation |
Answer: (B) A-II, B-IV, C-I, D-III
Explanation
If virtual memory is 32 MB and physical memory is 4 MB with page size 2 KB, calculate the number of frames available in physical memory.
Answer: (B) 2048
Explanation
Which is the correct sequence for an interrupt service routine?
A. Save contents of processor registers
B. Turn the interrupt facility on
C. Service the device whose flag is set
D. Check which flag is set
E. Restore contents of processor registers
Answer: (B) D, B, C, A, E
Explanation
Which of the following does not interrupt a running process?
Answer: (C) Scheduler
Explanation
The displayed disk-scheduling graph processes requests 28, 36, 45, 84, 125, 170 and 172, then wraps to the low end. Which algorithm does it represent?
Answer: (D) C-LOOK
Explanation
Given the displayed process burst times and priorities, which is a value of average waiting time under priority scheduling?
Answer: (D) 8.2
Explanation
The entire set of parameters, including the return address, stored for a procedure invocation is called
Answer: (A) stack frame
Explanation
Consider the following processes, with arrival and burst times in milliseconds. What is the average waiting time using non-preemptive shortest-job-first scheduling?
| Process | Arrival time | Burst time |
|---|---|---|
| P₁ | 0 | 5 |
| P₂ | 2 | 3 |
| P₃ | 2 | 2 |
| P₄ | 5 | 3 |
| P₅ | 6 | 1 |
Answer: (D) 3.2 ms
Explanation
Calculate the average response time with non-preemptive priority scheduling. Assume all processes arrive at time 0 and lower numbers mean higher priority.
| Process | Burst time | Priority |
|---|---|---|
| P₁ | 5 | 3 |
| P₂ | 3 | 1 |
| P₃ | 2 | 5 |
| P₄ | 3 | 4 |
| P₅ | 1 | 2 |
Answer: (A) 5.6 ms
Explanation
For the given arrival-time and burst-time process set, find the average weighted turnaround time using Highest Response Ratio Next (HRN).
| Process | Arrival time | Burst time |
|---|---|---|
| P₁ | 0 | 5 |
| P₂ | 2 | 3 |
| P₃ | 2 | 2 |
| P₄ | 5 | 3 |
| P₅ | 6 | 1 |
Answer: (B) 2.834 ms
Explanation
When shortest-job-first scheduling causes a process to face partial starvation and wait longer to execute, which algorithm addresses this problem?
Answer: (A) Round Robin
Explanation
For the given arrival-time and burst-time process set, what is the average turnaround time using first-come, first-served scheduling?
| Process | Arrival time | Burst time |
|---|---|---|
| P₁ | 0 | 5 |
| P₂ | 2 | 3 |
| P₃ | 2 | 2 |
| P₄ | 5 | 3 |
| P₅ | 6 | 1 |
Answer: (C) 7.0 ms
Explanation
Which of the following statements are TRUE
about mutual exclusion in concurrent
programming ?
A. Mutual exclusion ensures that only one
process can be in a critical section at any given
time.
B. Mutual exclusion are designed to prevent
conflicts and ensure that only one process can
access shared resources at a time.
C. Mutual exclusion can use various algorithms
to ensure that processes do not enter the critical
section simultaneously.
D. Mutual exclusion allows multiple processes to
access the critical section simultaneously to
improve performance.
Answer: (A) (A), (B), (C) Only
Explanation
Which of the following statements are TRUE
about Privileged Instructions ?
A. It can only be executed by the Operating
System kernel and not by user applications.
B. It is designed to perform operations that can
directly affect the hardware or system state such
as I/O operations or changing memory
management setting.
C. User applications can execute privileged
instructions if they have to correct permissions,
set by the Operating System.
D. It usually executed in user mode to ensure
the safety and security of the system.
Answer: (A) (A) and (B) Only
Explanation
Which of the following statements are TRUE
about Process Control Block (PCB) ?
A. The PCB contains information about the
process state, such as whether it is running,
waiting or terminated
B. The PCB includes the program code and data
segments of the process
C. The PCB stores the process's memory
management information, such as page tables
and segment tables
D. The PCB is used to track process scheduling
information and CPU registers for process
execution
Answer: (C) (A), (C) and (D) Only
Explanation
Which of the following is NOT a
requirement for Banker's algorithm to
grant a resource request ?
The Banker’s Algorithm is a critical deadlock avoidance method in operating systems, designed to facilitate resource allocation without causing deadlock. It operates by maintaining information about the maximum resources each process may require, the currently allocated resources and the available resources in the system. The algorithm checks each resource request to determine if granting it would leave the system in a safe state, meaning that there is always a sequence in which all processes can complete their execution without getting stuck due to resource unavailability. Each process must specify its maximum demand for each resource type before it starts execution. When a process requests additional resources, the algorithm checks if granting the request will keep the system in a safe state. If so, the resources are allocated; otherwise the process must wait until its request can be safely fulfilled.
Answer: (D) The process must be the only one requesting resources.
Explanation
Which data structure does the Banker's
Algorithm use to maintain the state of
available, maximum and allocated
resources ?
The Banker’s Algorithm is a critical deadlock avoidance method in operating systems, designed to facilitate resource allocation without causing deadlock. It operates by maintaining information about the maximum resources each process may require, the currently allocated resources and the available resources in the system. The algorithm checks each resource request to determine if granting it would leave the system in a safe state, meaning that there is always a sequence in which all processes can complete their execution without getting stuck due to resource unavailability. Each process must specify its maximum demand for each resource type before it starts execution. When a process requests additional resources, the algorithm checks if granting the request will keep the system in a safe state. If so, the resources are allocated; otherwise the process must wait until its request can be safely fulfilled.
Answer: (D) Matrices and Vectors
Explanation
What is the significance of the Banker's
algorithm in terms of resource
management?
The Banker’s Algorithm is a critical deadlock avoidance method in operating systems, designed to facilitate resource allocation without causing deadlock. It operates by maintaining information about the maximum resources each process may require, the currently allocated resources and the available resources in the system. The algorithm checks each resource request to determine if granting it would leave the system in a safe state, meaning that there is always a sequence in which all processes can complete their execution without getting stuck due to resource unavailability. Each process must specify its maximum demand for each resource type before it starts execution. When a process requests additional resources, the algorithm checks if granting the request will keep the system in a safe state. If so, the resources are allocated; otherwise the process must wait until its request can be safely fulfilled.
Answer: (A) It enures that all processes can finish their execution without deadlock.
Explanation
What is the primary goal of the Banker's
Algorithm?
The Banker’s Algorithm is a critical deadlock avoidance method in operating systems, designed to facilitate resource allocation without causing deadlock. It operates by maintaining information about the maximum resources each process may require, the currently allocated resources and the available resources in the system. The algorithm checks each resource request to determine if granting it would leave the system in a safe state, meaning that there is always a sequence in which all processes can complete their execution without getting stuck due to resource unavailability. Each process must specify its maximum demand for each resource type before it starts execution. When a process requests additional resources, the algorithm checks if granting the request will keep the system in a safe state. If so, the resources are allocated; otherwise the process must wait until its request can be safely fulfilled.
Answer: (A) To allocate resources optimally
Explanation
What information is used to determine if
a resource request can be granted ?
The Banker’s Algorithm is a critical deadlock avoidance method in operating systems, designed to facilitate resource allocation without causing deadlock. It operates by maintaining information about the maximum resources each process may require, the currently allocated resources and the available resources in the system. The algorithm checks each resource request to determine if granting it would leave the system in a safe state, meaning that there is always a sequence in which all processes can complete their execution without getting stuck due to resource unavailability. Each process must specify its maximum demand for each resource type before it starts execution. When a process requests additional resources, the algorithm checks if granting the request will keep the system in a safe state. If so, the resources are allocated; otherwise the process must wait until its request can be safely fulfilled.
Answer: (A) Available resources and current allocation of each process
Explanation
What is the output of the following program ? # include <stdio.h> # define SQR(x) (x*x) int main () {int a, b=3; a=SQR(b+2); printf("%d",a); return 0; }
Answer: (B) 11
Explanation
The head of a moving head disk with 200 tracks, numbered 0 to 199, has just finished a request at track 125, and currently serving a request at track 143. The queue of requests is given in the FIFO order as 86, 147, 91, 177, 94, 150, 102, 175, 130. What will be the total number of head movements required to satisfy these requests for SCAN algorithm ?
Answer: (B) 169 cylinders
Explanation
Given as 4 GB (= 4.3 x 10° bytes) of virtual space and typical page size of 4 KB and each page table entry is 5 bytes. How many virtual pages would this imply ? What is the size of whole page table ?
Answer: (A) 107500 and 20480 bytes
Explanation
In Linux, where is the user password stored ?
Answer: (C) /etc/passwd
Explanation
Indexed/ grouped allocation is useful as :
A. It supports both sequential and direct access.
B. Entire block is available for data.
C. It does not require lots of space for keeping pointers.
D. No external fragmentation. Choose the correct answer from the options given below :
Answer: (D) (A), (B) and (D) Only
Explanation
Which of the following statements are CORRECT ?
A. A process always check state of currently executing process to enter critical schema.
B. Spin locks uses busy waiting.
C. Periodically testing a variable until some value appear is known as busy waiting.
D. Critical region is a part of program, where shared memory is kept.
E. Printer daemon, continuously checks to see if there are any file to be printed. Choose the correct answer from the options given below :
Answer: (C) (B) and (D) Only
Explanation
The steps for analysis and design of object oriented system.
A. Draw interaction diagrams
B. Draw state chart and object diagram
C. Draw use case and activity diagram
D. Draw component and deployment diagram
E. Draw class diagram Choose the correct answer from the options given below :
Answer: (D) C → A → E → B → D
Explanation
Arrange the following levels of interrupt protection within the Linux Kernel, in the order of increasing priority.
A. user mode programs
B. bottom half interrupt handlers
C. kernel system service routines
D. top half interrupt handlers Choose the correct answer from the options given below : ()
A. ,
B. , (P), ©
Answer: (B) (A), ©, (8), ©)
Explanation
Result of *{x.s=y.s¥ is : [s|s[ec] er]. | J 1 M S, | CA B | 2/]N 1] P, | AB M |r |s3]uH |v, |} ve £ 4 G | Null] Null [s[s [ec] Pr]o] J 1 M S, | CA B}| 2 | N | P, | AB
| X (S, Si, C) | Y (S, P, D) |
|---|---|
(J, 1, M) (B, 2, N) (R, 3, H) (T, 4, G) | (J, S₁, CA) (B, P₁, AB) (R, D₁, DC) (A, H₁, MD) |
Answer: (B) (J, 1, M, S₁, CA); (B, 2, N, P₁, AB); (R, 3, H, D₁, DC); (A, Null, Null, H₁, MD)
Explanation
A machine has 3 page frames and the reference stream A, B, C, D, A, B, E, A, B, C, D, E, B, A, B. If P and Q are the page faults under FIFO and LRU respectively, what is (P, Q)?
Answer: (D) (11, 12)
Explanation
A disk has 60 cylinders. Requests are 10, 22, 20, 2, 40, 6, 38; the head starts at 20. Movement by one cylinder takes 2 ms. Under SSTF, what is the total service time?
Answer: (C) 120 milliseconds
Explanation
A Linux filesystem has 2 KB blocks and 32-bit disk addresses. An i-node has 12 direct pointers, one single-indirect pointer, and one double-indirect pointer. Approximately what is the largest representable file?
Answer: (B) 513 Mbytes
Explanation
In a single-level page-table system with the page table in memory, TLB hit rate is 80%. TLB search takes 15 ns and a main-memory access takes 150 ns. What is the effective memory access time?
Answer: (B) 195
Explanation
Assuming that the system call fork () never fails, consider the following C programs P1 and
P2 executed on a UNIX / Linux system:
/*P1+] j= P2+]
int main () { int main () {
fork (): fork ():
fork (): printf("Happy\n"):
fork (): fork()
printf("Happy\n"): printf("Happy\n"):
} fork( ):
printf("Happy\n");
}
Statement I: P1 displays "Happy" 8 times.
Statement II: P2 displays "Happy" 12 times.
In the light of the above statements, choose the correct answer from the options given below
Answer: (C) Statement I is correct but Statement II is false
Explanation
A disk has the parameters shown in the table. If T is the capacity of one track and S is the capacity of one surface, what is (T,S)?
| Disk parameter | Value |
|---|---|
| Sector size | 512 bytes |
| Tracks per surface | 2,000 |
| Sectors per track | 50 |
| Platters | 5 double-sided |
| Average seek time | 10 ms |
Answer: (C) (25 K, 50,000 K)
Explanation
Using the disk parameters shown in the table, what is the disk capacity?
| Disk parameter | Value |
|---|---|
| Sector size | 512 bytes |
| Tracks per surface | 2,000 |
| Sectors per track | 50 |
| Platters | 5 double-sided |
| Average seek time | 10 ms |
Answer: (B) 500,000 K
Explanation
Using the disk parameters shown in the table, assess the statements.
Statement I: The disk has 2,000 cylinders.
Statement II: 51,200 bytes is not a valid block size for this disk.
| Disk parameter | Value |
|---|---|
| Sector size | 512 bytes |
| Tracks per surface | 2,000 |
| Sectors per track | 50 |
| Platters | 5 double-sided |
| Average seek time | 10 ms |
Answer: (A) Both statements are true.
Explanation
If the disk rotates at 5,400 rpm, approximately what is the maximum rotational delay?
| Disk parameter | Value |
|---|---|
| Sector size | 512 bytes |
| Tracks per surface | 2,000 |
| Sectors per track | 50 |
| Platters | 5 double-sided |
| Average seek time | 10 ms |
Answer: (A) 0.011 seconds
Explanation
If one track can be transferred per revolution, what is the data-transfer rate for the disk in the table rotating at 5,400 rpm?
| Disk parameter | Value |
|---|---|
| Sector size | 512 bytes |
| Tracks per surface | 2,000 |
| Sectors per track | 50 |
| Platters | 5 double-sided |
| Average seek time | 10 ms |
Answer: (D) 2,250 KBytes/second
Explanation
39 System Software and Operating System questions appear in the UGC NET Computer Science papers held between 2020–2025, and all of them are on this page with their answer key.
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System Software and Operating System appears in every recent UGC NET Computer Science paper, across all 4 sittings covered here. Its share of the paper makes it worth revising thoroughly rather than sampling.
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