Operating Systems & System Software: Kernels, Processes, Memory, File Systems

What is an Operating System (OS)?

An operating system (OS) is system software that manages hardware and software resources, provides common services for computer programs, and acts as an intermediary between users and hardware. It controls execution of programs, manages file systems, and handles input/output operations.

Key Functions of an OS

mindmap
  root((Operating System Functions))
    Kernel["Core component (manages CPU, memory, devices)"]
    ProcessManagement["Creates, schedules, terminates processes"]
    MemoryManagement["Allocation, protection, swapping"]
    FileSystem["Organizes, stores, retrieves files"]
    IOManagement["Handles input/output devices"]
    Security["User authentication, permissions, protection"]
    UserInterface["CLI, GUI, APIs"]

Types of Operating Systems

System Software

System software supports application software and computer hardware. It includes:

• Operating Systems (Windows, Linux, macOS)
• Utility Programs (Antivirus, Disk Cleanup, File Compression)
• Device Drivers (Printer drivers, GPU drivers)
• Language Processors (Compilers, Interpreters)

How System Software Works

sequenceDiagram
    User->>Application: Runs a program
    Application->>OS: Requests resources (CPU, memory)
    OS->>Hardware: Allocates resources
    Hardware->>OS: Returns data
    OS->>Application: Provides services
    Application->>User: Executes task

Process Management

A process is an instance of a program in execution. The OS manages processes using:

• Process States: New, Ready, Running, Waiting, Terminated.
• Process Control Block (PCB): Stores process info (PID, registers, state).
• Scheduling Algorithms: First-Come-First-Served (FCFS), Shortest Job First (SJF), Round Robin (RR).

Process States Transition

stateDiagram-v2
    [*] --> New
    New --> Ready : Admitted
    Ready --> Running : CPU Allocated
    Running --> Waiting : I/O Request
    Waiting --> Ready : I/O Complete
    Running --> Terminated : Exit
    Terminated --> [*]

Worked Example: Bank Customer Queue (Round Robin Scheduling)

• Scenario: A bank has 3 customers (A, B, C) with tasks taking 5, 3, and 8 minutes respectively.
• Time Quantum (TQ) = 2 minutes
  • Cycle 1: A (2/5), B (2/3), C (2/8)
  • Cycle 2: A (3/5), B (1/3), C (6/8)
  • Cycle 3: A (Terminated), B (Terminated), C (4/8)
  • Cycle 4: C (4/8) → Total Time = 12 minutes

Memory Management

The OS allocates and manages memory (RAM) for processes using:

• Partitioning: Fixed vs. Dynamic
• Paging: Divides memory into fixed-size blocks.
• Segmentation: Divides memory into variable-sized segments.
• Virtual Memory: Uses disk space (swap file) when RAM is full.

Memory Allocation Strategies

File Systems

A file system organizes and stores files on storage devices (HDD, SSD). Key components:

• File: Collection of related data (e.g., report.docx).
• Directory: Contains files and subdirectories.
• File Attributes: Name, size, type, permissions.

Common File Systems

Worked Example: File Permissions (Linux)

• Scenario: A file data.txt has permissions rw-r--r--.
  • Owner (User): Read (r), Write (w)
  • Group: Read (r)
  • Others: Read (r)
• Command to change permissions:

  chmod 644 data.txt
  

In the Real World

1. eSewa (Nepal) uses a real-time OS to process payments instantly, ensuring low latency for transactions.
2. WhatsApp relies on a distributed OS (Google Cloud) to handle billions of messages globally without downtime.
3. NTC (Nepal Telecom) uses network OS (Cisco IOS) to manage routers and ensure stable internet connectivity.

Exam Tip

• Define clearly: Always explain terms like "process," "thread," and "virtual memory" with examples.
• Compare OS types: Questions often ask to differentiate between batch, time-sharing, and real-time OS.
• Diagrams are key: Draw process state transitions or memory allocation strategies in exams.
• Real-world links: Relate concepts to apps like Khalti (process scheduling) or Daraz (file systems for order storage).

Shows kernel, shell, and application layers in an OS. (Image: Andrew S. Tanenbaum, Herbert Bos, Public domain, via Wikimedia Commons)

Depicts directories, files, and attributes in a tree structure. (Image: Rasulnrasul, CC BY-SA 4.0, via Wikimedia Commons)