Introduction to Operating Systems & System Structures
Introduction
An Operating System (OS) is one of the most important software components in a computer system. It acts as a bridge between computer hardware and users, allowing users to interact with the system efficiently. Without an operating system, a computer would simply be a collection of electronic components unable to perform useful tasks.
Every device we use today—including desktops, laptops, smartphones, tablets, smart TVs, and even smartwatches—relies on an operating system to manage hardware resources, execute programs, provide security, and ensure smooth communication between software and hardware.
Popular operating systems include:
Microsoft Windows
Linux
macOS
Android
iOS
Unix
Operating systems have evolved significantly from simple batch-processing systems to sophisticated distributed and cloud-based operating systems capable of managing millions of users simultaneously.
What is an Operating System?
Definition
An Operating System (OS) is system software that manages computer hardware and software resources while providing services to application programs and users.
Formal Definition
An Operating System is system software that acts as an interface between users and computer hardware by managing resources such as CPU, memory, storage devices, input/output devices, and software applications.
Objectives of an Operating System
The primary objectives of an operating system are:
Provide user convenience
Efficiently manage hardware resources
Execute programs
Manage memory
Control input/output devices
Provide security and protection
Manage files and directories
Facilitate communication between hardware and software
History and Evolution of Operating Systems
The evolution of operating systems can be divided into several generations.
1. First Generation (1940–1955)
Characteristics
No operating system
Programs executed manually
Machine language programming
One program at a time
Examples
ENIAC
UNIVAC
Problems
Very slow
Manual operation
No automation
2. Second Generation (1955–1965)
Batch Operating Systems
Programs were grouped into batches and executed one after another.
Advantages
Reduced manual intervention
Better CPU utilization
Disadvantages
No interaction with users
Long waiting time
3. Third Generation (1965–1980)
Multiprogramming
Multiple programs were kept in memory simultaneously.
Features
CPU scheduling
Memory management
Spooling
Time-sharing
Examples:
IBM OS/360
UNIX
4. Fourth Generation (1980–Present)
Development of
Personal computers
Graphical User Interface (GUI)
Distributed systems
Mobile operating systems
Cloud operating systems
Artificial Intelligence support
Examples
Windows 11
Ubuntu Linux
Android
macOS
iOS
Types of Operating Systems
Operating systems are classified based on how they manage resources and users.
1. Batch Operating System
Definition
A Batch Operating System collects jobs and executes them sequentially without user interaction.
Characteristics
No user interaction
Jobs processed in batches
Suitable for repetitive tasks
Advantages
High throughput
Efficient for large jobs
Disadvantages
Long waiting time
No immediate response
Examples
IBM Batch Systems
Applications
Payroll processing
Bank transactions
Utility billing
2. Time-Sharing Operating System
Definition
A Time-Sharing OS allows multiple users to use the computer simultaneously by allocating a small time slice to each process.
Features
Multi-user
Interactive
Fast response
CPU scheduling
Advantages
Efficient CPU utilization
Multiple users simultaneously
Examples
UNIX
Linux
3. Distributed Operating System
Definition
A Distributed OS manages multiple computers connected through a network and makes them appear as a single system.
Characteristics
Resource sharing
Transparency
Scalability
Advantages
High reliability
Better performance
Load balancing
Examples
Amoeba
Plan 9
4. Real-Time Operating System (RTOS)
Definition
A Real-Time Operating System processes data within a fixed time limit.
Types
Hard Real-Time
Missing a deadline may cause system failure.
Examples
Aircraft systems
Medical devices
Soft Real-Time
Occasional deadline misses are acceptable.
Examples
Multimedia systems
Video conferencing
Popular RTOS
VxWorks
QNX
FreeRTOS
5. Multiprocessor Operating System
Definition
Supports multiple CPUs working together.
Features
Parallel processing
Increased performance
Better reliability
Examples
Linux SMP
Windows Server
6. Mobile Operating System
Definition
Designed specifically for smartphones and tablets.
Features
Touch interface
Battery optimization
Wireless communication
Mobile applications
Examples
Android
iOS
Components of an Operating System
The operating system consists of several major components.
1. Kernel
Definition
The Kernel is the core component of an operating system that manages hardware resources and provides essential services.
Functions
Process management
Memory management
Device management
File system management
Interrupt handling
CPU scheduling
Types
Monolithic Kernel
Microkernel
Hybrid Kernel
Examples
Linux Kernel
Windows NT Kernel
2. Shell
Definition
The Shell is a command interpreter that acts as an interface between users and the operating system.
Types
Command Line Shell
Examples
Bash
PowerShell
CMD
Graphical Shell
Examples
Windows Explorer
GNOME
KDE
Functions
Execute commands
Launch applications
Manage files
Automate tasks using scripts
3. System Calls
Definition
A System Call is a mechanism through which user programs request services from the operating system kernel.
Categories
Process Control
Create process
End process
Load program
File Management
Open file
Read file
Write file
Delete file
Device Management
Read device
Write device
Information Management
Get system information
Set system information
Communication
Send message
Receive message
Operating System Architecture
Operating system architecture determines how different OS components are organized.
1. Monolithic Architecture
Definition
All operating system services run inside one large kernel.
Advantages
Fast execution
Efficient communication
Disadvantages
Difficult maintenance
Low modularity
Examples
Linux
UNIX
2. Layered Architecture
Definition
The operating system is divided into layers, with each layer providing services to the layer above it.
Advantages
Easy debugging
Better modularity
Easier maintenance
Disadvantages
Slower than monolithic systems
Example
THE Operating System
3. Microkernel Architecture
Definition
Only essential functions remain inside the kernel; all other services run in user space.
Advantages
High security
Better reliability
Easy updates
Disadvantages
More communication overhead
Slightly slower
Examples
MINIX
QNX
Mach
Services Provided by an Operating System
An operating system offers various services to users and application programs.
1. Program Execution
Loads and executes programs.
2. Process Management
Creates, schedules, and terminates processes.
3. Memory Management
Allocates and deallocates RAM efficiently.
4. File System Management
Creates, deletes, copies, and organizes files.
5. Device Management
Controls printers, disks, keyboards, and other peripherals.
6. Security and Protection
Provides authentication, authorization, and access control.
7. Error Detection
Detects and reports hardware and software errors.
8. Networking
Supports communication over local and global networks.
9. Resource Allocation
Distributes CPU time, memory, and storage among processes.
10. User Interface
Provides GUI and CLI for user interaction.
Booting Process
Definition
Booting is the process of starting a computer and loading the operating system into main memory (RAM).
Types of Booting
Cold Boot
Starting the computer from a powered-off state.
Warm Boot
Restarting the computer without turning off the power.
Windows Booting Process
Power button pressed.
BIOS or UEFI initializes hardware.
POST (Power-On Self-Test) checks hardware components.
Bootloader (Windows Boot Manager) is loaded.
Windows kernel (
ntoskrnl.exe) is loaded into memory.Device drivers are initialized.
User login screen appears.
Desktop environment loads.
Linux Booting Process
Power on.
BIOS/UEFI initialization.
POST.
GRUB bootloader starts.
Linux Kernel loads.
initorsystemdstarts.Services and daemons are initialized.
Login prompt or graphical desktop appears.
Booting Process Flow Diagram
Power ON
│
▼
BIOS / UEFI
│
▼
POST
│
▼
Boot Loader
│
▼
Kernel Loaded
│
▼
Drivers Loaded
│
▼
System Services Started
│
▼
Login Screen
│
▼
Desktop Ready
Basic Command-Line Interface (CLI) Commands
Windows CMD
| Command | Purpose |
|---|---|
dir | List files and folders |
cd | Change directory |
mkdir | Create a new folder |
rmdir | Remove a folder |
copy | Copy files |
del | Delete files |
cls | Clear screen |
ipconfig | Display IP configuration |
tasklist | Show running processes |
shutdown /s | Shut down the computer |
Linux Terminal
| Command | Purpose |
|---|---|
pwd | Show current directory |
ls | List files |
cd | Change directory |
mkdir | Create a directory |
rm | Remove files |
cp | Copy files |
mv | Move or rename files |
cat | Display file contents |
top | Monitor running processes |
df -h | Show disk usage |
free -h | Display memory usage |
Practical Activities
Activity 1: Research Different Types of Operating Systems
Objective: Understand various operating systems and their applications.
| Operating System Type | Example | Common Use |
|---|---|---|
| Batch | IBM Batch Systems | Payroll processing |
| Time-sharing | Linux | Multi-user servers |
| Distributed | Amoeba | Cluster computing |
| Real-time | FreeRTOS | Embedded systems |
| Multiprocessor | Windows Server | Data centers |
| Mobile | Android | Smartphones |
Activity 2: Identify OS Components
Kernel
Manages CPU, memory, and devices.
Runs in privileged mode.
Shell
Accepts user commands.
Launches programs and scripts.
System Calls
Provide controlled access to kernel services such as file operations, process creation, and device communication.
Activity 3: Demonstrate the Booting Process
Windows
Restart the computer.
Observe BIOS/UEFI logo.
Watch the Windows loading screen.
Log in and open Task Manager to view running system processes.
Linux
Restart the computer.
Observe the GRUB menu.
Boot into Linux.
Use the following commands:
systemctl status dmesg | less journalctl -bto inspect boot and system logs.
Activity 4: Compare OS Architectures
| Feature | Monolithic | Layered | Microkernel |
|---|---|---|---|
| Performance | Excellent | Good | Moderate |
| Security | Moderate | Good | Excellent |
| Modularity | Low | High | Very High |
| Fault Isolation | Low | Moderate | High |
| Example | Linux | THE OS | MINIX |
Activity 5: Execute Basic CLI Commands
Windows (CMD)
dir
cd Documents
mkdir DemoFolder
echo Hello > demo.txt
copy demo.txt DemoFolder
tasklist
ipconfig
Linux (Terminal)
pwd
ls
mkdir demo
cd demo
touch sample.txt
echo "Hello Linux" > sample.txt
cat sample.txt
df -h
free -h
Advantages of Operating Systems
Simplifies computer usage.
Efficiently manages hardware resources.
Supports multitasking and multi-user environments.
Provides security and data protection.
Offers user-friendly interfaces.
Enables networking and communication.
Supports application software execution.
Disadvantages of Operating Systems
Can consume significant system resources.
May introduce security vulnerabilities if not updated.
Licensing costs for some commercial operating systems.
Hardware compatibility issues may arise.
Complex operating systems require regular maintenance and updates.
Summary
An Operating System is the foundation of every modern computing device. It manages hardware, provides services to applications, and offers an interface for users. Over the years, operating systems have evolved from simple batch-processing systems to sophisticated platforms supporting distributed computing, real-time processing, multiprocessor systems, and mobile devices. Understanding OS components such as the Kernel, Shell, and System Calls, along with architectures like Monolithic, Layered, and Microkernel, is essential for students and professionals. Knowledge of the booting process and command-line tools further strengthens practical system administration and troubleshooting skills.
Frequently Asked Questions (FAQs)
1. What is an Operating System?
An Operating System is system software that manages computer hardware, software resources, and provides services to application programs.
2. What is the difference between a Kernel and a Shell?
The Kernel is the core component that directly manages hardware and system resources, whereas the Shell provides the interface through which users interact with the operating system.
3. What are System Calls?
System calls are programmed interfaces that allow user applications to request services from the operating system kernel, such as file access, process creation, and memory management.
4. What is the purpose of the booting process?
The booting process initializes hardware, loads the operating system kernel into memory, starts essential services, and prepares the system for user interaction.
5. Which OS architecture is the most secure?
Microkernel architecture is generally considered the most secure because it keeps only essential services inside the kernel, reducing the trusted computing base and improving fault isolation.
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