cs3451 unit 1

1. CS3451 – Introduction to
Operating Systems
UNIT I – INTRODUCTION

2. Introduction to Operating System
• An Operating System (OS) is an interface
between user and hardware
• Controls execution of programs
• Manages system resources efficiently
• Examples: Windows, Linux, Android, iOS

3. Goals of Operating System
• Execute user programs
• Make system convenient to use
• Efficient utilization of hardware
• Ensure security and reliability

4. Computer System Components
• Hardware – CPU, Memory, I/O devices
• Operating System – Resource manager
• Application Programs – User-level software
• Users – Humans or other systems

5. Diagram: Computer System
User → Application Programs → Operating System → Hardware

6. User View of Operating System
• Designed for ease of use
• Performance and security oriented
• Desktop, mobile, and voice-based interaction
• Touch and gesture interfaces in mobiles

7. System View of Operating System
• OS acts as resource allocator
• Manages CPU, memory, I/O, and storage
• Ensures fairness and efficiency

8. Components of Operating System
• Shell – User interface
• Kernel – Core OS services
• User Mode and Kernel Mode

9. Diagram: OS Components
User → Shell → Kernel → Hardware

10. Computer System – Elements &
Organization
• CPU connected to device controllers
• Shared system bus
• Device controllers manage specific devices
• Parallel execution possible

11. Diagram: System Organization
CPU ↔ System Bus ↔ Memory & Device Controllers

12. Interrupts
• Hardware interrupts
• Software interrupts (System calls)
• Interrupt vector table
• Interrupt Service Routine (ISR)

13. Diagram: Interrupt Handling
Device → Interrupt → CPU → ISR → Resume Execution

14. Storage Structure
• Main Memory (RAM) – Volatile
• Secondary Storage – HDD, SSD
• Tertiary Storage – Backup media
• Memory hierarchy

15. I/O Structure
• Interrupt-driven I/O
• Direct Memory Access (DMA)
• CPU free during DMA transfer

16. Diagram: DMA
Device Controller → Main Memory (Without CPU intervention)

17. Evolution of Operating Systems
• Single Processor Systems
• Multiprocessor Systems
• Multicore Systems
• Clustered Systems

18. Multiprogramming
• Multiple processes in memory
• CPU always kept busy
• Improves CPU utilization

19. Diagram: Multiprogramming
Memory contains multiple processes

20. Multitasking
• Rapid switching between processes
• Interactive systems
• Response time < 1 second

21. Dual Mode Operation
• User Mode – Limited privileges
• Kernel Mode – Full privileges
• Mode bit for protection

22. Timer
• Prevents infinite loops
• Generates interrupt after time expires
• Ensures CPU control to OS

23. Operating System Services
• User Interface
• Program Execution
• I/O Operations
• File System
• Communication
• Security

24. User & OS Interface
• Command Line Interface
• Graphical User Interface
• Touch Interface
• Voice Interface
• Gesture Interface

25. System Calls
• Interface between user programs and OS
• Executed in kernel mode
• Provides controlled access to hardware

26. Diagram: System Call
User Program → System Call → Kernel → Hardware

27. Types of System Calls
• Process Control
• File Management
• Device Management
• Information Maintenance
• Communication

28. System Programs
• File manipulation
• Status information
• Programming language support
• Program loading and execution

29. OS Design & Implementation
• User goals – Convenience, reliability
• System goals – Efficiency, flexibility
• Mechanisms and Policies

30. Operating System Structures
• Monolithic
• Layered
• Microkernel
• Modular
• Hybrid

31. Diagram: OS Structures
Different kernel organization approaches

32. Hybrid Systems
• macOS and iOS
• Android
• Combination of monolithic and microkernel
concepts

33. Summary
• OS is the backbone of computer systems
• Manages hardware and software
• Provides services for efficient execution