Operating Systems

[Buela_Vigneswaran]

Operating Systems

1. Introduction to Operating Systems

• Definition:
  • An OS is software that acts as an intermediary between computer hardware and the user, providing an environment for execution.
• Functions of an OS:
  • Process Management: Handling processes, including creation, scheduling, and termination.
  • Memory Management: Allocating memory to processes and ensuring efficient use.
  • File System Management: Managing files, directories, and permissions.
  • Device Management: Managing hardware devices and providing drivers.
  • Security and Access Control: Protecting data and managing user access.

2. Process Management

• Process:
  • A program in execution, consisting of a program counter, stack, and data.
• Process Scheduling:
  • Algorithms: First-Come-First-Served (FCFS), Shortest Job Next (SJN), Round Robin (RR), Multilevel Queue Scheduling.
• Concurrency and Synchronization:
  • Ensuring that multiple processes execute safely, without conflicts.
  • Mechanisms: Semaphores, Mutexes, Monitors, Deadlock Prevention.
• Inter-Process Communication (IPC):
  • Communication between processes via pipes, message queues, shared memory.

3. Memory Management

• Memory Hierarchy:
  • Registers, Cache, Main Memory, Disk Storage.
• Techniques:
  • Paging: Dividing memory into fixed-size pages.
  • Segmentation: Dividing memory into variable-sized segments.
  • Virtual Memory: Using disk storage as an extension of RAM (e.g., swapping).
• Memory Allocation:
  • Fixed Partitioning, Dynamic Partitioning, Buddy System.

4. File System Management

• File Concepts:
  • File attributes, file types, file names, and file access permissions.
• File Operations:
  • Creation, deletion, reading, writing, and manipulation of files.
• File System Types:
  • FAT (File Allocation Table), NTFS, ext4, HFS+.
• Directory Structure:
  • Single-level, Two-level, Hierarchical, and Network file systems (NFS).

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5. Device Management

• I/O Management:
  • Communication between the OS and hardware devices (input devices, output devices, storage).
• Device Drivers:
  • Programs that control and facilitate communication with hardware devices.
• I/O Scheduling Algorithms:
  • FCFS, SSTF (Shortest Seek Time First), SCAN, C-SCAN.

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6. Security and Protection

• Access Control:
  • Authentication (e.g., passwords, biometrics) and authorization (user permissions).
• Malware Prevention:
  • Virus protection, firewalls, and system monitoring.
• Encryption:
  • Securing data using cryptographic methods.
• Audit Trails:
  • Recording system activities to detect unauthorized actions.

7. Types of Operating Systems

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• Batch OS:
  • Executes a series of jobs without interaction (e.g., early mainframes).
• Time-Sharing OS:
  • Multiple users can share system resources (e.g., UNIX, Linux).
• Real-Time OS:
  • Meets time constraints and responds immediately to inputs (e.g., embedded systems, robotics).
• Distributed OS:
  • Manages a collection of independent systems as one (e.g., Google File System, Hadoop).
• Network OS:
  • Supports networking features and remote access (e.g., Windows Server).

8. Virtualization

• Definition:
  • Running multiple OS instances on a single physical machine using a hypervisor.
• Types:
  • Full Virtualization: The guest OS is unaware it’s being virtualized (e.g., VMware, Hyper-V).
  • Paravirtualization: The guest OS is aware and cooperates with the hypervisor (e.g., Xen).
• Containers:
  • Lightweight virtualization where applications run in isolated environments (e.g., Docker, Kubernetes).

9. Performance Evaluation

• Metrics:
  • CPU Utilization, Memory Utilization, I/O Throughput, Response Time.
• Load Balancing:
  • Distributing work evenly across available resources to optimize performance.
• Benchmarking:
  • Comparing the performance of different systems or configurations.