Operating System Fundamentals and Interview Questions
Operating System Basic Definitions
Q1. Define Operating System.
Answer: An Operating System (OS) is system software that acts as an interface between the user and computer hardware and manages system resources efficiently.
Q2. What is a Process?
Answer: A process is a program in execution. It consists of program code, data, stack, and resources allocated by the operating system.
Q3. Define PCB.
Answer: PCB (Process Control Block) is a data structure used by the OS to store information about a process, such as process ID, state, registers, and scheduling information.
Q4. What is Deadlock?
Answer: Deadlock is a situation in which two or more processes wait indefinitely for resources held by each other.
Q5. What is Paging?
Answer: Paging is a memory management technique in which logical memory is divided into pages and physical memory into frames.
Q6. What is Virtual Memory?
Answer: Virtual memory is a memory management technique that allows execution of large programs even when physical memory is limited.
Q7. What is Linux?
Answer: Linux is a free and open-source operating system based on UNIX, developed by Linus Torvalds.
Process Management and CPU Scheduling
Q1. Explain Process States with Diagram.
Answer: A process passes through different states during execution:
New → Ready → Running → Waiting → Ready → Terminated
States:
- New: Process is being created.
- Ready: Waiting for CPU allocation.
- Running: Instructions are being executed.
- Waiting: Waiting for I/O operation.
- Terminated: Process has completed execution.
Importance: Helps the OS manage processes efficiently.
Q2. Explain Process Control Block (PCB).
Answer: PCB is a data structure maintained by the OS for each process.
Contents:
- Process ID
- Process State
- Program Counter
- CPU Registers
- Memory Information
- Scheduling Information
Functions:
- Tracks process execution.
- Supports context switching.
- Stores process-related information.
Q3. Explain FCFS Scheduling.
Answer: FCFS (First Come First Serve) schedules processes according to arrival order.
Advantages:
- Simple
- Easy implementation
Disadvantages:
- High waiting time
- Convoy effect
Q4. Explain Round Robin Scheduling.
Answer: Round Robin scheduling allocates the CPU to each process for a fixed time quantum.
Features:
- Preemptive algorithm.
- Fair CPU allocation.
- Suitable for time-sharing systems.
Advantages:
- Good response time.
- No starvation.
Disadvantages:
- More context switching.
Memory and Resource Management
Q5. Explain Deadlock and its Conditions.
Answer: Deadlock occurs when processes wait indefinitely for resources.
Four Necessary Conditions:
- Mutual Exclusion
- Hold and Wait
- No Preemption
- Circular Wait
Deadlock occurs only when all four conditions exist simultaneously.
Q6. Explain Paging.
Answer: Paging divides memory into fixed-size pages and frames.
Advantages:
- No external fragmentation.
- Efficient memory utilization.
Working:
- Logical memory → Pages
- Physical memory → Frames
Pages are mapped into frames using page tables.
Q7. Explain Virtual Memory.
Answer: Virtual memory allows programs larger than RAM to execute.
Advantages:
- Better memory utilization.
- Supports multiprogramming.
- Large program execution.
Demand Paging:
Pages are loaded only when required.
Q8. Explain File Allocation Methods.
Answer:
1. Contiguous Allocation
File stored in continuous memory blocks.
2. Linked Allocation
Blocks connected through pointers.
3. Indexed Allocation
Separate index block stores addresses of file blocks.
Linux Architecture and Interface
Q9. Explain Linux Architecture.
Answer: Linux architecture consists of four layers:
User
↓
Shell
↓
Kernel
↓
HardwareKernel Functions:
- Memory Management
- Process Management
- File Management
- Device Management
Q10. Differentiate CLI and GUI.
| CLI | GUI |
|---|---|
| Command-based | Graphical Interface |
| Fast | Easy to use |
| Less memory | More memory |
| Requires commands | User friendly |
Advanced OS Concepts and Comparisons
Q1. Explain Types of Operating Systems.
Answer:
Batch Operating System
Processes jobs in batches.
Multiprogramming OS
Multiple programs stay in memory simultaneously.
Time Sharing OS
Many users share the CPU.
Real-Time OS
Provides immediate response.
Personal Computer OS
Used in desktops and laptops.
Mobile OS
Used in smartphones.
Examples: Windows, Linux, Android.
Q2. Compare FCFS, SJF and Round Robin Scheduling.
| FCFS | SJF | RR |
|---|---|---|
| Arrival order | Shortest job first | Time quantum based |
| Simple | Minimum waiting time | Fair scheduling |
| Non-preemptive | Usually non-preemptive | Preemptive |
| High waiting time | Starvation possible | More context switching |
Q3. Explain Memory Management Techniques.
Answer:
Swapping
Transfers processes between RAM and disk.
Paging
Divides memory into pages and frames.
Segmentation
Divides memory into logical segments.
Virtual Memory
Allows execution of large programs.
Demand Paging
Loads pages only when needed.
Q4. Explain Disk Scheduling Algorithms.
Answer:
FCFS
Serves requests in arrival order.
SSTF
Chooses the nearest request.
SCAN
Moves the head in both directions.
C-SCAN
Moves the head in one direction only.
LOOK
Stops at the last request.
Advantages:
- Reduced seek time.
- Better disk performance.