Unit 1: Introduction to Operating Systems
1. Introduction
• An Operating System (OS) is system software that manages hardware resources and
provides services for application programs.
• It acts as a mediator between hardware and users, offering an environment for program
execution.
Key Functions of an OS:
1. Resource Allocation: Manages hardware resources (CPU, memory, I/O devices) efficiently.
2. Process Management: Handles process creation, scheduling, and termination.
3. Memory Management: Allocates and deallocates memory spaces as needed.
4. Security and Protection: Ensures that the system is secure from internal and external
threats.
5. File System Management: Manages data storage and access in files.
2. Need for an Operating System
• Resource Management: The OS allows multiple programs to run concurrently without
conflicts, allocating system resources (CPU, memory, etc.) efficiently.
• Program Execution: It provides services to execute user and system programs smoothly.
• Convenience for Users: Users do not need to manage hardware details manually.
• Security and Protection: Protects the system from unauthorized users or programs.
Exam Tip: Mention the role of OS in managing both hardware and software resources effectively.
3. Evolution of Operating Systems
Operating systems evolved to address the growing complexity and capabilities of computer systems:
1. Serial Processing (1940s-50s):
• No operating system; users interacted directly with hardware.
• Inefficient as users waited for long periods for results.
2. Batch Processing (1950s-60s):
• Jobs were collected and executed in batches without user interaction.
• Advantage: High throughput due to sequential job execution.
• Disadvantage: No real-time interaction with users.
3. Multiprogramming (1960s):
, • Multiple jobs reside in memory, and the OS switches between them to optimize CPU
usage.
• Example: IBM OS/360.
• Advantage: Higher CPU utilization compared to batch systems.
• Disadvantage: Complex memory management and scheduling.
4. Time-Sharing Systems (1970s):
• Allows multiple users to interact with the system simultaneously using terminals.
• The CPU gives each user a time slice, creating the illusion of concurrent execution.
• Example: UNIX
• Advantage: Real-time interaction with users, multi-user support.
• Disadvantage: Overhead from context switching.
5. Real-Time Operating Systems (RTOS):
• Designed to process data and execute tasks within a guaranteed time frame.
• Hard Real-Time Systems: Critical systems where deadlines must be met (e.g., aerospace
control).
• Soft Real-Time Systems: More flexible with deadlines (e.g., multimedia).
• Advantage: Predictable response times.
• Disadvantage: Complex to design and manage.
6. Modern Operating Systems:
• Support multitasking, multithreading, networking, security, and GUIs.
• Example: Windows, macOS, Linux.
• Advantage: High interactivity, multitasking, and user-friendly interfaces.
7. Missing OS:
• Refers to an OS that is not directly visible or traditionally accessible to users but
works in the background, managing specific devices or systems, often referred to as
"embedded" systems.
• Example: Embedded operating systems in appliances, vehicles, or smartphones.
• Advantage: Tailored for specific hardware, ensuring high efficiency and reliability in
constrained environments.
• Disadvantage: Limited functionality compared to general-purpose OS, specific to
one task or device.
Key Concepts for Evolution:
• Mention the importance of multiprogramming and time-sharing in improving efficiency.
• Highlight UNIX as a major breakthrough in OS development.
1. Introduction
• An Operating System (OS) is system software that manages hardware resources and
provides services for application programs.
• It acts as a mediator between hardware and users, offering an environment for program
execution.
Key Functions of an OS:
1. Resource Allocation: Manages hardware resources (CPU, memory, I/O devices) efficiently.
2. Process Management: Handles process creation, scheduling, and termination.
3. Memory Management: Allocates and deallocates memory spaces as needed.
4. Security and Protection: Ensures that the system is secure from internal and external
threats.
5. File System Management: Manages data storage and access in files.
2. Need for an Operating System
• Resource Management: The OS allows multiple programs to run concurrently without
conflicts, allocating system resources (CPU, memory, etc.) efficiently.
• Program Execution: It provides services to execute user and system programs smoothly.
• Convenience for Users: Users do not need to manage hardware details manually.
• Security and Protection: Protects the system from unauthorized users or programs.
Exam Tip: Mention the role of OS in managing both hardware and software resources effectively.
3. Evolution of Operating Systems
Operating systems evolved to address the growing complexity and capabilities of computer systems:
1. Serial Processing (1940s-50s):
• No operating system; users interacted directly with hardware.
• Inefficient as users waited for long periods for results.
2. Batch Processing (1950s-60s):
• Jobs were collected and executed in batches without user interaction.
• Advantage: High throughput due to sequential job execution.
• Disadvantage: No real-time interaction with users.
3. Multiprogramming (1960s):
, • Multiple jobs reside in memory, and the OS switches between them to optimize CPU
usage.
• Example: IBM OS/360.
• Advantage: Higher CPU utilization compared to batch systems.
• Disadvantage: Complex memory management and scheduling.
4. Time-Sharing Systems (1970s):
• Allows multiple users to interact with the system simultaneously using terminals.
• The CPU gives each user a time slice, creating the illusion of concurrent execution.
• Example: UNIX
• Advantage: Real-time interaction with users, multi-user support.
• Disadvantage: Overhead from context switching.
5. Real-Time Operating Systems (RTOS):
• Designed to process data and execute tasks within a guaranteed time frame.
• Hard Real-Time Systems: Critical systems where deadlines must be met (e.g., aerospace
control).
• Soft Real-Time Systems: More flexible with deadlines (e.g., multimedia).
• Advantage: Predictable response times.
• Disadvantage: Complex to design and manage.
6. Modern Operating Systems:
• Support multitasking, multithreading, networking, security, and GUIs.
• Example: Windows, macOS, Linux.
• Advantage: High interactivity, multitasking, and user-friendly interfaces.
7. Missing OS:
• Refers to an OS that is not directly visible or traditionally accessible to users but
works in the background, managing specific devices or systems, often referred to as
"embedded" systems.
• Example: Embedded operating systems in appliances, vehicles, or smartphones.
• Advantage: Tailored for specific hardware, ensuring high efficiency and reliability in
constrained environments.
• Disadvantage: Limited functionality compared to general-purpose OS, specific to
one task or device.
Key Concepts for Evolution:
• Mention the importance of multiprogramming and time-sharing in improving efficiency.
• Highlight UNIX as a major breakthrough in OS development.
