OS Combine

School Information

• Institution: School of Computer Sciences and Engineering

• Department: Computer Science and Engineering

• Semester: 5th

• Subject Name: Operating System

• Subject Code: 17YCT502

• Faculty: Dr. M. Juned

Unit-1: Operating Systems Overview

What is an Operating System?

• Definition: An Operating System (OS) is a system software that acts as an intermediary/interface between users and computer hardware.

• Components of a Computer System:

  • Hardware

  • Software (includes Application Software and System Software/OS)

Goals of Operating Systems

• Execute user programs to solve user problems

• Make the computer system convenient to use

• Efficient utilization of computer hardware

Architecture of Operating Systems

• Modern operating systems are complex and provide many services, supporting various hardware and software.

• Architectural Types:

  • Monolithic Architecture

  • Layered Architecture

  • Microkernel Architecture

Monolithic Architecture

• All components are contained within a single kernel.

• Pros: Efficient communication among components

• Cons: Hard to detect subtle errors

Layered Architecture

• Groups similar function components into layers.

• Each layer communicates only with adjacent layers.

• Challenges: Can lead to decreased system throughput.

Microkernel Architecture

• Minimal services provided to keep the kernel small and scalable.

• Pros: Highly modular and portable.

• Cons: Can affect system performance due to increased intermodule communication.

Main Functions of Operating Systems

Memory Management

• Definition: Management of Primary Memory or Main Memory

• Activities:

  • Tracking memory usage

  • Allocating and deallocating memory for processes

Processor Management

• Definition: Management of process scheduling in a multiprogramming environment.

• Activities:

  • Tracking processor status

  • Allocating processor to processes

Device Management

• Definition: Manages device communication via drivers.

• Activities:

  • Tracking devices

  • Allocating devices efficiently

File Management

• Organizes files in directories; manages file access and resources.

Other Functions

• Security, Control over system performance, and Coordination between software and users

Evolution of Operating Systems

1. First Generation (1940s - Early 1950s)

   • No OS; programming in machine language

2. Second Generation (1955 - 1965)

   • Introduction of GMOS, a single-stream batch processing OS

3. Third Generation (1965 - 1980)

   • Development of multiprogramming

4. Fourth Generation (1980-Present)

   • Rise of PCs and graphical OS like Windows/Mac OS, including more sophisticated features

Unit-1 Module-2: Types of Operating Systems

1. Batch Operating System

• Does not directly interact with users; processes jobs in batches.

• Advantages:

  • Efficient processing for similar jobs

• Disadvantages:

  • Debugging can be difficult; jobs may wait indefinitely if one fails.

2. Time-Sharing Operating Systems

• Allows multiple users to access the system simultaneously by splitting CPU time among processes.

• Advantages:

  • Efficient CPU utilization and less idle time

3. Distributed Operating Systems

• Coordinating multiple interconnected computers for resource sharing and remote access.

• Advantages:

  • Fault tolerance and scalability

4. Network Operating System

• Manages data, users, and security across a network of machines.

• Advantages:

  • Centralized management and remote access capabilities

5. Real-Time Operating System

• Responds to input within specific time constraints.

• Divided into Hard (strict timing) and Soft (less strict timing)

6. Embedded Operating System

• Built directly into devices (e.g., medical equipment, cars).

7. Multiprogramming Operating System

• Executes multiple jobs at once by managing job scheduling.

Virtual Machines

• Simulates a physical computer environment, allowing multiple OS instances on single hardware.

Unit-2 Module-1: Processes

Definition

• A process is a program in execution and represents a unit of work.

• Sections of a Process: Stack, Heap, Text, Data

Process Control Block (PCB)

• Contains information necessary for process management including state, number, and resources being used

Scheduler Types

• Long-term Scheduler: Chooses which process to bring to the ready state.

• Short-term Scheduler: Selects which process from the ready queue to execute.

• Medium-term Scheduler: Swaps processes in and out of memory, optimizing multiprogramming.

Unit-2 Module-2: CPU Scheduling

Criteria for CPU Scheduling

1. CPU Utilization

2. Throughput

3. Turnaround Time

4. Waiting Time

5. Response Time

Scheduling Algorithms

• First-Come, First-Serve (FCFS): Processes scheduled in order of arrival.

• Shortest Job Next (SJN): Prioritizes tasks with the shortest execution times.

• Priority Scheduling: Based on process priority; potential starvation risk.

• Round Robin: Each process gets a fixed time to execute, promotes fairness.

• Multilevel Feedback Queue: Processes can move between queues as needed.

Unit-3 Module-1: Interprocess Communication

Definition

• Mechanism that allows processes to communicate and synchronize their actions.

Concepts

• Race Condition: Occurs when processes access shared data concurrently.

• Critical Section: Code section where shared resources are accessed, requiring synchronization.

Techniques for Synchronization

• Mutexes, Semaphores, Monitors, and Condition Variables.

Unit-4: Memory Management

Techniques

• Contiguous Allocation: Each process requires a contiguous memory allocation.

• Paging: Divides memory into fixed-size pages to avoid fragmentation.

• Segmentation: Divides memory into segments based on logical divisions of programs.

Fragmentation Types

1. Internal Fragmentation: Memory allocated but not used within a block.

2. External Fragmentation: Free memory is available but not contiguous.

Unit-5: I/O Management

Definition

• Process of managing input and output devices and operations.

Disk Scheduling Algorithms

• FCFS: Serves requests in order of arrival.

• SSTF: Shortest seek time first.

• SCAN: Moves in one direction satisfying requests and returns.

• C-SCAN: Similar to SCAN but jumps to the opposite end once it reaches one end.

• LOOK: Stops moving when no more requests exist in the current direction.

Cache Memory

• Temporary data storage to speed up data access.

• Advantages: Faster than main memory, reduces access times.

• Disadvantages: Expensive and limited capacity.

Files

• A named collection of related information stored on secondary storage.

• Attributes: Name, Identifier, Type, Location, Size, Protection.

• Operations: Creating, Writing, Reading, Repositioning, Deleting, and Protection.

Directory Structures

1. Single-level: All files in one directory.

2. Two-level: Each user has a directory.

3. Tree-structured: Hierarchical structure for better organization.

Security Overview

Computer Security

• Protecting systems from unauthorized access and maintaining confidentiality and integrity of data.

Types of Security Threats

• Malware, Phishing, Spoofing, Eavesdropping, Social Engineering.

Prevention Measures

• Regular updates, using secure networks, strong passwords, and user education.