IT-501 Operating System - 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
   aExplain the different functions of an operating system and discuss the various services provided by an operating system.
   How to answer

   • Define operating system as resource manager and extended machine
   • List functions: process, memory, file, device, protection management
   • List OS services: program execution, I/O, file system, communication, error detection, resource allocation, accounting, protection
2. 7 Marks
   bExplain different types of systems calls with suitable example.
   How to answer

   • Define system call as interface between process and OS
   • Classify into process control, file management, device management, information maintenance, communication
   • Give example for each e.g. fork, open/read/write, ioctl, getpid, pipe
3. 7 Marks
   aDefine process synchronization and explain Peterson solution algorithms.
   How to answer

   • Define process synchronization and race condition, critical section problem
   • Present Peterson's solution for two processes with flag and turn variables
   • Explain mutual exclusion, progress, bounded waiting satisfaction
4. 7 Marks
   bConsider 3 processes $P_1$, $P_2$ and $P_3$, which require 5, 7 and 6 time units and arrive at time 0, 1 and 4. Draw the Gant chart, process completion sequence and average waiting time for.

   1. i)Round Robin scheduling with CPU quantum of 2 time units.
   2. ii)FCFS
   How to answer

   • List burst times 5,7,6 and arrival times 0,1,4 for P1,P2,P3
   • Construct Gantt chart for Round Robin quantum 2 and for FCFS
   • Compute waiting and turnaround times and average waiting time for both
5. 7 Marks
   aWhat are the differences of internal and external memory Fragmentation?
   How to answer

   • Define internal fragmentation: wasted space inside fixed partition
   • Define external fragmentation: free space scattered between partitions
   • Compare cause, occurrence in paging vs segmentation, and remedies like compaction, paging
6. 7 Marks
   bConsider the following snapshot of a system: Allocation, Max, Available as per table. Answer the following questions using the banker's algorithm:

   1. a)What is the content of the matrix Need?
   2. b)Is the system in a safe state?
   3. c)If a request from process $P_1$ arrives for (0, 4, 2, 0), can the request be granted immediately?

   How to answer

   • Compute Need = Max - Allocation matrix
   • Apply Banker's safety algorithm to find safe sequence with Available (1,5,2,0)
   • Check request (0,4,2,0) from P1 for Need and Available and safety
7. 7 Marks
   aConsider the following page reference string: 1, 2, 3, 4, 2, 1, 5, 6, 2, 1, 2, 3, 7, 6, 3, 2, 1, 2, 3, 6. How many page faults would occur for the following replacement algorithms, assuming one and three frames? Remember all frames are initially empty, so your first unique pages will all cost one fault each. - LRU replacement - FIFO replacement
   How to answer

   • State reference string 1,2,3,4,2,1,5,6,2,1,2,3,7,6,3,2,1,2,3,6 and frames initially empty
   • Simulate LRU replacement counting faults for one and three frames
   • Simulate FIFO replacement counting faults for one and three frames
8. 7 Marks
   bOn a simple paging system with $2^{24}$ bytes of physical memory, 256 pages of logical address space, and a page size of $2^{10}$ bytes, how many bits are in logical address?
   How to answer

   • Compute logical address bits = page number bits + offset bits
   • Page offset = log2(2^10)=10 bits, pages 256 => 8 bits
   • Total logical address = 18 bits
9. 7 Marks
   aSuppose 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 requests, in FIFO order is 86, 1470, 913, 1774, 948, 1509, 1022, 1750, 130 Starting from the current head position, what is the total distance (in cylinders) that the disk arm moves to satisfy all the pending requests, for each of the following disk-scheduling algorithms?

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

   • Note current head 143, previous 125 indicating increasing direction, queue list
   • Compute total head movement for FCFS in given order, for SSTF nearest, for SCAN elevator
   • Compare distances
10. 7 Marks
    bWhat are the typical access rights that may be granted or denied to a particular user for a particular file?
    How to answer

    • List read, write, execute, append, delete, list, ownership
    • Explain allow/deny per user/group/others with protection bits
    • Give Unix example rwx
11. 7 Marks
    aGive five memory partitions of 100 KB, 500 KB, 200 KB, 300 KB and 600 KB (in order), how would each of the first-fit, best-fit, and worst-fit algorithms place processes of 212 KB, 417 KB, 112 KB, and 426 KB (in order): Which algorithm makes the most efficient use of memory?
    How to answer

    • List partitions 100,500,200,300,600 and processes 212,417,112,426
    • Simulate first-fit, best-fit, worst-fit placement in order
    • Identify most efficient algorithm by wastage/unallocated processes
12. 7 Marks
    bWhen multiple interrupts from different devices appear at about the same time, a priority scheme could be used to determine the order in which the interrupts would be serviced. Discuss what issues need to be considered in assigning priorities to different interrupts.
    How to answer

    • Explain simultaneous interrupts and priority resolution via polling/daisy chain/vectored
    • Discuss issues: urgency, device speed, data loss, starvation, response time
    • Discuss fairness and dynamic vs static priority
13. 7 Marks
    aExplain the process state transition diagram used in multiprogramming environment. Describe the fields in a Process Control Block (PCB).
    How to answer

    • Draw 5-state diagram: new, ready, running, waiting/blocked, terminated with transitions
    • Explain scheduler actions: admit, dispatch, interrupt, I/O wait, wakeup
    • List PCB fields: PID, state, PC, registers, scheduling info, memory, I/O, accounting
14. 7 Marks
    bWhat are various criteria for a good process scheduling algorithm? Explain any two preemptive scheduling algorithms in brief.
    How to answer

    • List criteria: CPU utilization, throughput, turnaround, waiting, response time, fairness
    • Explain two preemptive algorithms e.g. SRTF and Round Robin / Priority preemptive
    • Compare features and use
15. 14 Marks
    Write short notes on (Any Three):

    1. a)Distributed System
    2. b)Thrashing
    3. c)Inter Process Communication
    4. d)System Calls
    How to answer

    • Define each chosen topic with key characteristics
    • Explain working with example/diagram
    • Mention advantages, disadvantages and OS use