OS Basics: Definitions, Functions, Services & Evolution

TAKEAWAYS:

• An operating system (OS) is a system software that acts as an intermediary between hardware and user applications, managing resources efficiently.
• The five primary functions of an OS are process management, memory management, file management, device management, and system calls.
• OS provides services like user interface, program execution, I/O operations, file system management, error detection, and resource allocation.
• The evolution of OS from batch processing to real-time systems reflects advancements in hardware and user demands.
• Types of OS (batch, time-sharing, distributed, network, real-time) are designed for specific use cases, each with unique advantages and limitations.
• Modern OS like Linux, Windows, and macOS incorporate multitasking, multithreading, and virtualization to optimize performance.

1. Definition of an Operating System (OS)

An Operating System (OS) is a system software that manages computer hardware and software resources, providing common services for computer programs. It acts as an interface between the user and the hardware, ensuring efficient execution of programs.

Key Roles of an OS

• Resource Allocator: Decides which program gets system resources (CPU, memory, I/O devices).
• Control Program: Controls execution of programs to prevent errors and improper use of resources.
• User Interface: Provides a platform for users to interact with the computer (CLI, GUI, or batch).

Why is an OS Necessary?

Without an OS, programs would directly interact with hardware, leading to:

• Inefficient resource usage (e.g., two programs trying to use the printer simultaneously).
• Hardware conflicts (e.g., two programs accessing the same memory location).
• No user-friendly interaction (users would need to write low-level commands).

2. Functions of an Operating System

An OS performs five primary functions to ensure smooth operation:

3. Services Provided by an OS

An OS offers services to both users and applications:

A. User-Oriented Services

• User Interface: CLI (Command Line Interface) or GUI (Graphical User Interface).
  • Example: Windows GUI vs. Linux Terminal.
• Program Execution: Loading and running programs.
  • Example: Double-clicking an .exe file in Windows.
• I/O Operations: Managing input/output devices.
  • Example: Reading from a USB drive or printing a document.
• File System Management: Creating, deleting, and modifying files.
  • Example: Saving a document in Google Docs (stored on cloud).
• Error Detection & Recovery: Handling system crashes and data corruption.
  • Example: Windows Blue Screen of Death recovery.
• Accounting: Keeping track of resource usage (e.g., CPU time, memory).
  • Example: Billing in cloud services (AWS, Google Cloud).

B. System-Oriented Services

• Resource Allocation: Assigning CPU, memory, and I/O devices to processes.
• Security: Protecting system resources from unauthorized access.
  • Example: Password protection in Windows or Linux.
• Protection & Isolation: Preventing one process from interfering with another.
  • Example: Running multiple apps in different windows without crashes.

4. Evolution of Operating Systems

The development of OS has evolved through five generations, each improving efficiency and user experience:

5. Types of Operating Systems

Different OS types are designed for specific use cases:

6. Structure of an Operating System

An OS is organized in layers, where each layer provides services to the layer above it.

Layered Approach

• User Applications: Programs like browsers, games, or office suites.
• System Calls Interface: API for applications to request OS services.
• Kernel: Core OS component handling process, memory, and file management.
• Device Drivers: Software that controls hardware (printers, GPUs, etc.).
• Hardware: Physical components (CPU, RAM, disk).

Monolithic vs. Microkernel Architecture

7. Booting Process in an OS

When a computer starts, the OS undergoes a booting process to load and initialize:

sequenceDiagram
    participant BIOS
    participant MBR
    participant OS
    participant Kernel
    participant Services

    BIOS->>MBR: Power On Self Test (POST)
    MBR->>OS: Load Bootloader (GRUB)
    OS->>Kernel: Initialize Hardware
    Kernel->>Services: Load Device Drivers
    Services->>OS: Start User Interface
    OS->>User: Ready for Input

Steps in Booting

1. BIOS/UEFI: Checks hardware and loads the bootloader.
2. Bootloader (GRUB): Loads the OS kernel into memory.
3. Kernel Initialization: Sets up hardware and loads drivers.
4. User Interface: Loads GUI or CLI for user interaction.

8. System Calls

System calls are APIs that allow programs to request OS services. Common categories include:

In the Real World

1. eSewa (Nepal)

   • Idea Used: Process Management & Multitasking
   • How? eSewa’s backend runs multiple processes simultaneously (user authentication, payment processing, SMS notifications) without conflicts, thanks to the OS’s process scheduling and memory isolation.

2. Khalti (Digital Payments)

   • Idea Used: Real-Time OS (RTOS) & File System Management
   • How? Khalti’s servers use real-time processing to handle thousands of transactions per second. The OS ensures low-latency responses and secure file storage for transaction logs.

3. Pathao (Ride-Hailing App)

   • Idea Used: Distributed OS & Network OS
   • How? Pathao’s backend runs on a distributed system (multiple servers) managed by an OS that handles load balancing and fault tolerance. Drivers and riders interact via a network OS that synchronizes real-time location data.

4. NTC (Nepal Telecom) & Ncell

   • Idea Used: Device Management & System Calls
   • How? Telecom networks rely on OS-driven device drivers to manage modems, routers, and switches. System calls ensure efficient data transmission (e.g., send() for SMS routing).

5. Banking (Nabil Bank, Global IME)

   • Idea Used: Multitasking & Security Services
   • How? Banks use OS multitasking to run multiple services (ATM transactions, loan processing, fraud detection) simultaneously. Security services (encryption, access control) prevent unauthorized transactions.

Worked Example: Bank Loan Interest Calculation (OS Role)

Scenario: A bank processes loan applications where each application is a process managed by the OS.

Example Calculation: If a loan process takes 5 CPU cycles to compute interest and there are 10 loans, the OS’s scheduler ensures each gets 0.5 CPU time slices (round-robin scheduling).

Exam Tip

How This Unit is Examined

1. Definitions & Short Answers (2-5 marks)

   • Expect questions like:
     • "Define an operating system and list its three primary functions."
     • "Differentiate between batch OS and time-sharing OS."
   • Key Points to Remember:
     • OS = Resource allocator + Control program.
     • Five functions: Process, memory, file, device, system calls.
     • Types: Batch, time-sharing, distributed, network, RTOS.

2. Diagrams & Flowcharts (5-10 marks)

   • Draw:
     • Layered OS structure (user apps → kernel → hardware).
     • Booting process (BIOS → bootloader → kernel → UI).
     • System call categories (process control, file management, etc.).
   • Tip: Label every box and arrow clearly.

3. Comparisons (5-8 marks)

   • Compare:
     • Monolithic vs. Microkernel (structure, security, performance).
     • Batch vs. Time-Sharing OS (interactivity, efficiency).
   • Use tables (as shown above) for structured answers.

4. Scenario-Based Questions (8-10 marks)

   • Example: "A hospital management system runs on an OS. Explain how the OS ensures that patient records are securely stored and accessed only by authorized doctors."
   • Approach:
     • File system management (structured storage).
     • Security services (access control, encryption).
     • Process isolation (preventing unauthorized access).

5. Real-World Applications (3-5 marks)

   • Link OS concepts to Nepali companies (eSewa, Khalti, NTC) or global tech (Google, WhatsApp).
   • Example: "How does WhatsApp use an OS to handle millions of messages simultaneously?"
     • Answer: Uses multitasking (process management) and distributed OS (cloud servers).

Common Mistakes to Avoid

• Vague Definitions: Instead of "OS manages hardware," say "OS allocates CPU, memory, and I/O devices via scheduling and memory management."
• Incorrect Comparisons: Always use a table for side-by-side comparisons (e.g., batch vs. time-sharing).
• Ignoring Real-World Examples: Exams often ask for applications—relate OS concepts to eSewa, Khalti, or banking systems.
• Skipping Diagrams: If a question asks for a flowchart (e.g., booting process), always draw it—even if not explicitly asked.

Quick Revision Checklist

Before the exam, ensure you can: ✅ Define OS and list its five functions. ✅ Differentiate between batch, time-sharing, and real-time OS. ✅ Explain the layered structure of an OS (user → kernel → hardware). ✅ Describe the booting process in steps. ✅ Compare monolithic vs. microkernel architectures. ✅ Relate OS concepts to eSewa, Khalti, or banking systems. ✅ Draw system call categories and booting sequence diagrams.

A real picture of a data center server rack (to visualize where OS runs in real-world systems like eSewa or Khalti). (Image: Federal Bureau of Investigation, Public domain, via Wikimedia Commons)