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Operating System

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Module 1: Introduction to Operating Systems

  1. Q1a. What is operating system? (i) Collection of programs that manages hardware resources (ii) System service provider to the application programs20192m

    Module 1: Introduction to Operating Systems

    What is operating system?

    (i) Collection of programs that manages hardware resources
    (ii) System service provider to the application programs

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    Worked Solution

    Answer: Both (i) and (ii) are correct — complete definition is (i) + (ii)

    • If strictly single-choice, the most accepted textbook answer is (i) Collection of programs that manages hardware resources.
    • Standard definition: OS is system software that acts as intermediary between hardware and applications — it manages hardware resources and provides services to application programs. The question truncates option (ii), but both views are part of the full definition. In many PYQs this is marked as (i). If exam allows multiple correct, choose (i) and (ii).**
  2. Q1a. Which type of Operating System allows multiple users to access the system simultaneously? (i) Single-user OS (ii) Batch OS (iii) Multi-user OS (iv) Embedded OS20252m

    Module 1: Introduction to Operating Systems

    Which type of Operating System allows multiple users to access the system simultaneously?

    (i) Single-user OS
    (ii) Batch OS
    (iii) Multi-user OS
    (iv) Embedded OS

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    Answer: (iii) Multi-user OS

    • Multi-user OS (e.g., UNIX, Linux, Windows Server) allows multiple users to access the system simultaneously via terminals/remote sessions, with isolation and access control.
    • Single-user OS allows only one user at a time.
    • Batch OS executes jobs without user interaction.
    • Embedded OS is specialized for devices, not multi-user access.
  3. Q1c. What is the motive of using a Virtual Machine for an operating system? (i) Increase CPU throughput (ii) Run multiple operating systems on the same hardware (iii) Create databases (iv) Allow multiple threads to execute concurrently within a process20252m

    Module 1: Introduction to Operating Systems

    What is the motive of using a Virtual Machine for an operating system?

    (i) Increase CPU throughput
    (ii) Run multiple operating systems on the same hardware
    (iii) Create databases
    (iv) Allow multiple threads to execute concurrently within a process

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    Answer: (ii) Run multiple operating systems on the same hardware

    VM provides virtualization via hypervisor (Type1 bare-metal or Type2 hosted), allowing isolation, consolidation, testing and safe execution of multiple OS instances on one physical host. Not primarily for CPU throughput or databases.

  4. Q1d. What does a virtual machine do? (i) Manages only hardware devices (ii) Replaces the operating system (iii) Acts as a real machine but is implemented in software (iv) Removes the need for file systems20242m

    Module 1: Introduction to Operating Systems

    What does a virtual machine do?
    (i) Manages only hardware devices
    (ii) Replaces the operating system
    (iii) Acts as a real machine but is implemented in software
    (iv) Removes the need for file systems

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    Answer: (iii) Acts as a real machine but is implemented in software

    VM virtualizes CPU, memory, devices via hypervisor, presenting illusion of dedicated hardware to guest OS. Does not replace OS or remove file systems.

  5. Q2a. Explain system calls and their importance in Operating Systems. Discuss various categories of system calls.20257m

    Module 1: Introduction to Operating Systems

    Explain system calls and their importance in Operating Systems. Discuss various categories of system calls.

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    System Calls & Importance

    Interface for user programs to request kernel services (trap to kernel mode). Essential for protected hardware access.

    Categories

    1. Process Control: fork, exec, exit, wait, kill
    2. File Management: open, read, write, close, unlink
    3. Device Management: ioctl, read/write device
    4. Information Maintenance: getpid, time, sysinfo
    5. Communication: pipe, shmget, send/recv
    6. Protection: chmod, chown
      Importance: provides abstraction, security, portability. Invoked via syscall instruction (int 0x80 / syscall). Library wrappers handle setup.
  6. Q2b. Illustrate the concept of Virtual Machines.20257m

    Module 1: Introduction to Operating Systems

    Illustrate the concept of Virtual Machines.

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    Virtual Machine

    VM is software emulation of physical machine via hypervisor.

    • Type1 (bare-metal): hypervisor on hardware (VMware ESXi, Xen)
    • Type2 (hosted): hypervisor on host OS (VirtualBox)
      Components: virtual CPU, virtual memory, virtual devices. Isolation, snapshot, migration. Uses: server consolidation, testing, cloud. Advantages: isolation, resource utilization. Cost: overhead, I/O virtualization. Example: running Linux+Windows simultaneously.
Next moduleModule 2: Processes & Scheduling