CS-405 Operating Systems - Jun 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 are the five major activities of an operating system in regards to memory management?
   How to answer

   • Define memory management role of OS
   • List five activities: allocation/deallocation, tracking, protection, swapping, paging/segmentation management
   • Brief explanation of each activity
   • Diagram of memory manager interaction if needed
2. 7 Marks
   bList the functions of OS. How operating system perform management task in a system?
   How to answer

   • Define OS and its objectives
   • List functions: process, memory, file, device, security management
   • Explain management task: resource allocator and control program
   • Give example of scheduling and coordination
3. 7 Marks
   aGive an example of an application in which data in a file should be accessed in following order.

   1. i)Sequentially
   2. ii)Randomly
   How to answer

   • Define sequential access with example e.g. tape, log file, video playback
   • Define random/direct access with example e.g. database, array file
   • Justify why order matters for application
4. 7 Marks
   bSuppose that a disk drive has 5000 cylinders numbered 0 to 4999. The drive is currently serving a request at cylinder 143 and the previous request was at cylinder 125. The queue of pending request in FIFO order is - 86, 1470, 913, 1774, 948, 1509, 1022, 1750, 750, 750, 750, 130. Starting from current head position, what is the total distance that the disk arm moves to satisfy all pending request for each of following.

   1. i)SSTF
   2. ii)SCAN
   3. iii)LOOK
   How to answer

   • Note current head 143, previous 125 to infer direction
   • Apply SSTF ordering and sum seek distances
   • Apply SCAN and LOOK ordering and sum distances
   • Compare total head movements
5. 7 Marks
   aConsider a variant of the RR algorithm where the entries in the ready queue are pointers to the PCB

   1. i)What would be the effect of putting two pointers to the same process in the ready queue.
   2. ii)What would be the major advantages and drawback of this scheme.
   How to answer

   • Explain RR with PCB pointers
   • Effect of duplicate pointers: extra time slice / priority
   • Advantages: priority, favoring CPU-bound jobs
   • Drawbacks: unfairness, starvation, complexity
6. 7 Marks
   bHow many page faults occur for an optimal page replacement strategy for the following reference string for four page frames. 1 2 3 4 5 3 4 1 6 7 8 7 8 9 7 8 9 5 4 5 4 2
   How to answer

   • State optimal replacement rule: replace farthest future use
   • Simulate reference string with 4 frames step by step
   • Count hits vs faults
   • Give total page faults
7. 7 Marks
   aSuppose a process P wants to wait for two messages, one from mailbox A and one from mailbox B. What sequence of send and receive should it execute.
   How to answer

   • Explain mailbox / message passing
   • Discuss deadlock risk if blocking receive in order
   • Recommend non-blocking or select / receive from either
   • Give correct sequence
8. 7 Marks
   bWhy might a system use interrupt driven I/O to manage a single serial port but polling I/O to manage a front end processor, such as a terminal concentrator.
   How to answer

   • Define interrupt-driven vs polling I/O
   • Explain low-frequency single port favors interrupts
   • Explain high-frequency front-end favors polling overhead
   • Compare CPU overhead and latency
9. 7 Marks
   aWhat aspects of a distributed system would you select for a system running on a totally reliable network.
   How to answer

   • Define distributed system on reliable network
   • Select aspects: no need for retransmission, focus on performance, naming, migration
   • Explain which fault-tolerance can be relaxed
   • Give examples
10. 7 Marks
    bTo build robust distributed systems, you must know what kinds of failures can occur. List three possible types of failures in a distributed system.
    How to answer

    • Define distributed failures
    • List three types: crash, omission, Byzantine, timing
    • Brief description of each
    • Need for robust design
11. 7 Marks
    aDefine a semaphore for dining philosopher's problem.
    How to answer

    • Define semaphore and wait/signal
    • Show chopstick semaphores and mutex
    • Explain deadlock-free solution
    • Give pseudocode
12. 7 Marks
    bDescribe a method for process migration across different architecture running.

    1. i)The same operating system
    2. ii)Different operating system
    How to answer

    • Define process migration
    • Method for same OS: checkpoint and transfer state
    • Method for different OS/architecture: heterogeneous migration
    • Issues: address space, open files
13. 7 Marks
    aExplain concurrency controls? What are the differences between real and virtual concurrency?
    How to answer

    • Define concurrency control
    • Explain real vs virtual concurrency
    • Differences: true parallelism vs interleaving
    • Examples: multiprocessor vs single CPU
14. 7 Marks
    bHow process is differing from program? Describe process transition diagram in detail.
    How to answer

    • Define program vs process
    • List differences in table form
    • Draw 5/7-state process transition diagram
    • Explain transitions: new, ready, running, waiting, terminated
15. 14 Marks
    Write short notes on following. (any two)

    1. a)Deadlock prevention and avoidance
    2. b)Kernel architecture in Unix
    3. c)System calls
    How to answer

    • Select any two topics
    • Give definition and key points for each
    • Explain with example/diagram
    • Mention advantages/applications