📘 OS Notes

OS – Quick Revision Sheet

Operating System (OS) Notes

• Operating System (OS) is system software that manages hardware, software, and user interaction.
• Main Functions of an OS
  • Process management
  • Memory management
  • File system management
  • Device management
  • Security and access control
• Types of Operating Systems
  • Batch Operating System
  • Time-Sharing Operating System
  • Distributed Operating System
  • Real-Time Operating System (RTOS)
  • Network Operating System
• Process Management
  • A process is a program in execution
  • Process States:

    New → Ready → Running → Waiting → Terminated
            

  • Context Switching – Switching CPU between processes
• CPU Scheduling Algorithms
  • FCFS – First Come First Serve
  • SJF – Shortest Job First
  • Round Robin
  • Priority Scheduling
• Memory Management
  • RAM – Primary memory
  • Virtual Memory – Uses disk as extended RAM
  • Paging and Segmentation
• Deadlock
  • Occurs when processes wait indefinitely
  • Deadlock Conditions:
    • Mutual Exclusion
    • Hold and Wait
    • No Preemption
    • Circular Wait
• File System
  • Manages data storage and retrieval
  • Common file systems:
    • NTFS (Windows)
    • EXT4 (Linux)
    • FAT32
• Security in OS
  • User authentication and authorization
  • Access control and permissions
  • Process isolation

Next Topics: Linux commands, Windows internals, system calls, virtualization, containers.