AL-501 Operating System - Dec 2025 Question Paper

Under each question, How to answer lists the points an answer should cover, outlined by CampusPrep from the syllabus. Check the details against your textbook.

1. 7 Marks
   aWhat is Operating System? Discuss different types of Operating System.
   How to answer

   • Define operating system as resource manager and extended machine
   • List types: batch, multiprogrammed, time-sharing, real-time, distributed, networked, mobile
   • Explain characteristics of each type with examples
2. 7 Marks
   bWhat do you understand by system call? List and explain four system calls used for process management.
   How to answer

   • Define system call as interface between process and OS kernel
   • Explain mechanism: trap, mode switch
   • List four process management calls e.g. fork, exec, wait, exit
   • Explain purpose of each with example
3. 7 Marks
   aWhat are different functions provided by Operating System. Also discuss various services provided by an operating system by explaining different methods of providing these services through commands and system calls with suitable examples.
   How to answer

   • List OS functions: process, memory, file, device, security management
   • List OS services: UI, program execution, I/O, communication
   • Explain CLI vs GUI vs system calls for providing services
   • Give suitable examples
4. 7 Marks
   bDefine a file and explain the file concept in operating systems. Discuss the user's view and system programmer's view of a file system with suitable examples.
   How to answer

   • Define file as collection of related information
   • Explain file attributes, operations, types
   • Explain user view: naming, organization, access
   • Explain programmer view: FCB, open/close, file descriptors with examples
5. 7 Marks
   aDiscuss disk space allocation methods used in file systems. Explain contiguous, linked and indexed allocation with neat diagrams, advantages, and disadvantages.
   How to answer

   • Define contiguous, linked, indexed allocation
   • Draw block layout diagrams for each
   • Compare advantages: access speed, fragmentation
   • Compare disadvantages: external fragmentation, overhead, pointer loss
6. 7 Marks
   bExplain directory structures used in file systems. Also discuss file protection mechanisms and access control methods.
   How to answer

   • Explain single-level, two-level, tree, acyclic, general graph directories
   • Explain file protection: passwords, access lists
   • Explain access control: read/write/execute, owner/group/other
   • Give UNIX-type permission example
7. 7 Marks
   aWhat are threads? Explain the concept of multithreading. Compare user level threads and kernel-level threads in terms of creation, scheduling, performance and overhead.
   How to answer

   • Define thread vs process, benefits of multithreading
   • Explain multithreading models
   • Compare user-level vs kernel-level on creation, scheduling, performance, overhead in table
   • Give examples: pthreads, Java threads
8. 7 Marks
   bDiscuss the protection and security issues in operating systems. Explain various protection and security mechanisms such as authentication, access control, encryption and auditing.
   How to answer

   • Distinguish protection vs security goals
   • Explain authentication: passwords, biometrics
   • Explain access control, encryption, auditing
   • Discuss threats: malware, intrusions
9. 7 Marks
   aDefine deadlock. Explain deadlock characterization and discuss the four necessary conditions for deadlock to occur in a system.
   How to answer

   • Define deadlock with example
   • Explain characterization via resource allocation graph
   • Explain four Coffman conditions: mutual exclusion, hold and wait, no preemption, circular wait
   • State necessity of all four
10. 7 Marks
    bExplain producer consumer problem and its solution using semaphore. Explain how synchronization and mutual exclusion are achieved.
    How to answer

    • Describe bounded buffer producer-consumer problem
    • Give semaphore solution with mutex, empty, full and wait/signal
    • Show producer and consumer pseudocode
    • Explain how mutual exclusion and synchronization achieved
11. 7 Marks
    aConsider the following set of processes with their arrival time (AT) and burst time (BT). Draw the Gantt chart and calculate the average waiting time and average turnaround time for each process using the First Come First Serve (FCFS) and Shortest Remaining Time First (SRTF) scheduling algorithm.

    How to answer

    • Draw Gantt charts for FCFS and preemptive SRTF
    • Calculate CT, TAT = CT-AT, WT = TAT-BT for each process
    • Compute average WT and average TAT for both algorithms
    • Compare FCFS vs SRTF results
12. 7 Marks
    bExplain non-contiguous memory allocation techniques. Describe paging, segmentation and paged segmentation with neat diagrams.

    1. i)What is the content of the Need matrix?
    2. ii)Is the system in a safe state? If yes, justify your answer with a safe sequence.
    How to answer

    • Define non-contiguous allocation to reduce fragmentation
    • Explain paging with page table and address translation diagram
    • Explain segmentation with segment table diagram
    • Explain paged segmentation combining both
13. 7 Marks
    aConsider the following snapshot of a system and answer the following questions using the Banker's Algorithm:

    1. i)What is the content of the Need matrix?
    2. ii)Is the system in a safe state? If yes, justify your answer with a safe sequence.

    How to answer

    • Compute Need = Maximum - Allocated for P1, P2, P3
    • Check Available [7,7,10] against Needs to find safe sequence
    • Show step-wise allocation and release
    • Conclude safe/unsafe with sequence e.g. P2,P3,P1
14. 7 Marks
    bExplain I/O buffering and discuss its importance in improving I/O performance. Describe single buffering, double buffering and circular buffering.
    How to answer

    • Define I/O buffering to overlap CPU and I/O
    • Explain single buffering operation
    • Explain double buffering for parallel read/process
    • Explain circular buffering for bursty traffic
15. 7 Marks
    aExplain demand paging. For given page reference string, determine the number of page faults when three page frames are available using FIFO, LRU and Optimal page replacement algorithms. $0, 9, 0, 1, 8, 1, 8, 7, 8, 7, 1, 2, 8, 2, 7, 8, 2, 3, 8, 3$
    How to answer

    • Define demand paging and page fault handling steps
    • Simulate FIFO with 3 frames on reference string 0,9,0,1,8,1,8,7,8,7,1,2,8,2,7,8,2,3,8,3
    • Simulate LRU and Optimal similarly
    • Count faults for each and compare
16. 7 Marks
    bWrite short notes on any **TWO**:

    1. i)Critical Section Problem
    2. ii)Inter-Process Communication
    3. iii)Process State Diagram
    4. iv)Mobile Operating Systems
    How to answer

    • Select any two topics from list
    • Give definition, diagram/components where relevant
    • Explain working with examples
    • State uses/advantages