Concept of Operating Systems - NBCA/M-24 Answers

Q1. Compulsory Question

(a) Process Control Block

The Process Control Block (PCB) stores crucial information about each process, such as its ID, state, CPU register values, memory info, and I/O status, acting like a “resume” so it can resume from suspension.

(b) Deadlock Avoidance

Deadlock avoidance ensures the system never enters an unsafe state. Techniques like the Banker’s algorithm proactively check whether granting resources is safe before allocating them.

(c) Thrashing

Thrashing happens when the system constantly swaps pages in and out due to overload, leading to poor performance because processes do little real work.

(d) Real-time Processing

Real-time processing guarantees a response within strict deadlines, such as for medical or industrial systems. Hard real-time cannot miss deadlines; soft real-time tolerates minor misses.

(e) Swapping

Swapping moves entire processes between main memory and a backing store to free up space, enabling more multiprogramming but increasing latency.

Q2. What is an Operating System? Explain the role of OS as a resource manager. Explain its functions.

An Operating System is software that interfaces between users and hardware. As a resource manager, it handles:

  • CPU scheduling
  • Memory allocation
  • File and I/O device management
Major functions:
  • Process management
  • Memory management
  • File system management
  • I/O system management
  • Security and protection
  • Networking
  • User interface support

Q4. Define Deadlock. Explain its necessary conditions.

A deadlock is a situation where processes are blocked, each waiting for resources held by the other. The Coffman conditions for deadlock are:

  • Mutual Exclusion
  • Hold and Wait
  • No Preemption
  • Circular Wait
All must hold simultaneously for a deadlock to occur.

Q7. Explain paging with example, advantages, and disadvantages.

Paging divides memory into fixed-size frames and processes into same-size pages. A page table maps pages to frames. Example: A 16KB process with 4KB pages → 4 pages mapped to any available frames.
Advantages: No external fragmentation, supports virtual memory, flexible allocation.
Disadvantages: Page table overhead, internal fragmentation, slower address translation.

Q9. What is file management? Explain file access methods and file protection mechanisms.

File management organizes, stores, and protects data. Access methods:

  • Sequential access
  • Direct access
  • Indexed access
Protection mechanisms:
  • Access Control Lists (ACLs)
  • Passwords
  • Encryption
  • Group permissions
These ensure secure, consistent, and efficient file handling.