Unit 2: Operating system

Operating System (OS)

An Operating System (OS) is a system software that acts as an interface between the user and the computer hardware.
It manages hardware resources, runs applications, and controls overall system operations.

Examples: Windows, Linux, macOS, Android, iOS.

Functions of Operating System

An OS performs a variety of essential tasks to manage both hardware and software efficiently.

A. Process Management

• Creates, schedules, and terminates processes.
• Manages CPU time using scheduling algorithms (FCFS, Round Robin).
• Handles multitasking and multiprocessing.

B. Memory Management

• Allocates and deallocates memory.
• Handles virtual memory and paging.
• Ensures processes do not access each other’s memory.

C. File System Management

• Manages file creation, deletion, reading, writing.
• Organizes files in directories.
• Provides access permissions and security.

D. Device Management

• Manages input/output devices using device drivers.
• Maintains queues for devices.
• Controls device communication.

E. Security & Access Control

• Protects data from unauthorized access.
• Provides authentication (passwords, biometrics).
• Manages user accounts and permissions.

F. User Interface Management

• Provides Command-Line Interface (CLI) or Graphical User Interface (GUI).

G. Error Handling

• Detects hardware and software errors.
• Generates error messages and ensures safe recovery.

H. Resource Allocation

• Distributes resources (CPU, memory, devices) among users and tasks.

Types of Operating Systems

A. Batch Operating System

• Executes jobs in batches without user interaction.
• Used in payroll, billing systems.

B. Time-Sharing Operating System

• Multiple users access the system simultaneously.
• CPU time is divided among users.

C. Distributed Operating System

• Multiple computers connected to work as one system.
• Resource sharing across networks.

D. Real-Time Operating System (RTOS)

• Responds to inputs immediately.
• Used in robotics, medical systems, flight control.

E. Multiprogramming OS

• Multiple programs run simultaneously in memory.

F. Multitasking OS

• Allows multiple tasks to run at the same time.

G. Network Operating System (NOS)

• Manages network resources.
• Used in servers (Windows Server, Linux Server).

H. Mobile Operating Systems

• Designed for mobile devices.
• Android, iOS.

Classification of Operating Systems

OS can be classified based on features:

1. Based on User

• Single-user: Windows 10 Home

• Multi-user: UNIX, Linux

2. Based on Tasks

• Single-tasking: Early DOS

• Multitasking: Windows, Linux

3. Based on Processing

• Batch processing

• Real-time processing

• Time-sharing

4. Based on CPU:

• Uniprocessor OS: One CPU

• Multiprocessor OS: Multiple CPUs

5. Based on Interface:

• CLI: Command Line Interface

• GUI: Graphical User Interface

Elements of Command-Based OS

Command-based OS (CLI) uses text commands to interact with the system.

Examples:

• DOS (Disk Operating System)
• UNIX / Linux Terminal
• PowerShell
• Command Prompt (CMD)

Key Elements:

1. Command Prompt / Terminal - A text-based window to enter commands.

2. Commands - Single-line instructions.
   Examples:

   DIR    → list files  
   CD     → change directory  
   COPY   → copy files  
   RM     → remove files (Linux)  
   LS     → list files (Linux)
   

3. Syntax - Each command must follow a proper structure.
   Example:

   COPY source destination
   

4. Switches / Options - Modify how commands work.
   Example (Windows):

   DIR /P
   

   Example (Linux):

   LS -l
   

5. File Paths - Absolute and relative paths are used for navigation.

6. Shell- CLI interface like Bash, Zsh, Command.com.

Elements of GUI-Based Operating System

GUI systems use graphical elements such as windows, icons, buttons, and menus.

Examples:

• Windows OS
• macOS
• Ubuntu (GUI)
• Android
• iOS

Key Elements:

1. Desktop - Main working area with wallpaper and icons.
2. Icons - Small graphical symbols for applications/files.
3. Windows - Boxes to display files, apps, and settings.
4. Menus - Drop-down options (File, Edit, View, etc.).
5. Taskbar / Dock - Shows running applications and system notifications.
6. Buttons - Minimize, maximize, close button.
7. Pointer / Cursor - Controlled by mouse or touchpad.
8. Dialog Boxes - Pop-up windows for user input.
9. Touch Interface (mobile GUI) - Scroll, tap, swipe gestures.

Summary Table

Category	Command-Based OS (CLI)	GUI-Based OS
Interface	Text-based	Graphical
Ease of Use	Hard for beginners	Easy & user-friendly
Speed	Fast for experts	Slightly slower
Memory Use	Low	Higher
Examples	DOS, Linux terminal	Windows, Android
Input	Keyboard commands	Mouse, touch, keyboard
Best For	Programming, servers	Normal users, mobile devices

Computer Network 

A computer network is a system where two or more computers or devices are connected to share data, resources, and applications.

Key Goals of Networking

• Resource Sharing (printers, files, internet)
• Communication (email, messaging)
• Data Sharing (databases, cloud services)
• Centralized Management (servers, security policies)

Components of a Network

• Nodes (computers, printers, routers)
• Transmission Media (cables, wireless)
• Network Interface Cards (NIC)
• Connectivity Devices (switch, router, hub)
• Protocols (TCP/IP)

Types of Computer Networks

A. LAN (Local Area Network)

A LAN connects computers within a small geographical area, like:

• Home
• Office
• School
• Lab

Features

• High speed (100 Mbps – 10 Gbps)
• Low cost
• Owned and managed by one organization
• Uses switches, Ethernet, Wi-Fi

Examples

• College computer lab network
• Office internal network

B. MAN (Metropolitan Area Network)

A MAN covers a city or large campus, bigger than LAN but smaller than WAN.

Features

• Covers 10–50 km area
• High-speed connectivity
• Often maintained by telecom companies or ISPs

Examples

• Cable TV networks
• City-wide Wi-Fi
• University campus network

C. WAN (Wide Area Network)

A WAN covers a large geographical area such as a country or multiple countries.

Features

• Slow to moderate speed (depends on medium)
• Very large coverage (thousands of km)
• Uses routers, leased telephone lines, satellites, fiber optics
• Maintained by ISPs (Airtel, Jio, BSNL)

Examples

• The Internet (largest WAN)
• Banking networks (ATMs across cities)
• Multinational company networks

Comparison Table

Feature	LAN	MAN	WAN
Area	Small (building)	City/metropolitan	Worldwide
Speed	High	Medium–High	Low–Medium
Cost	Low	Medium	High
Ownership	Private	Public or private	Telecom/ISPs
Devices	Switch, Wi-Fi	Routers	Routers, satellites
Error rate	Low	Moderate	High

Data Communication

Data communication refers to the transfer of data between two devices through a communication medium.

Essential Elements of Data Communication

1. Sender – Device that sends data
2. Receiver – Device that receives data
3. Message – The data being transferred
4. Medium – Path (cable/wireless)
5. Protocol – Set of rules for communication (TCP/IP, HTTP)

Forms of Data Transmission

• Simplex - One-way communication only Example: TV broadcast
• Half-Duplex - Two-way communication but not simultaneously Example: Walkie-talkie
• Full-Duplex - Two-way communication at the same time Example: Mobile phone, Zoom call

Types of Transmission Media

1. Guided (Wired) Media

• Twisted pair cable
• Coaxial cable
• Fiber optics

2. Unguided (Wireless) Media

• Radio waves
• Microwaves
• Infrared
• Satellite

Network Topologies

Topology refers to the physical or logical arrangement of computers in a network.

A. Bus Topology

• All computers connected to a single central cable (bus).

Advantages

• Easy to install
• Low cost

Disadvantages

• If main cable fails, entire network stops
• Slow when many devices connect

B. Star Topology

• All computers connected to a central device (hub or switch).

Advantages

• Easy to manage
• Failure of one device does not affect others
• High performance

Disadvantages

• If hub/switch fails → network fails

C. Ring Topology

• Devices connected in a circular path; data moves in one direction.

Advantages

• Simple and organized
• Equal access for all nodes

Disadvantages

• Failure of one device breaks the whole network

D. Mesh Topology

• Each device connected to every other device.

Advantages

• Very reliable
• No data congestion

Disadvantages

• Very expensive
• Complicated to maintain

E. Tree (Hierarchical) Topology

• Combination of star + bus; arranged in hierarchical form.

Advantages

• Scalable
• Easy to expand

Disadvantages

• Higher cost than bus topology

F. Hybrid Topology

• Mixture of two or more topologies (star+ring, bus+mesh).

Advantages

• Flexible and scalable

Disadvantages

• Complex design
• High cost

Summary Table of Topologies

Topology	Key Feature	Strength	Weakness
Bus	Single cable	Cheap	Cable failure = network failure
Star	Central hub	Reliable	Hub failure is critical
Ring	Circular	Equal access	One point failure
Mesh	Every node connected	Highly reliable	Very costly
Tree	Hierarchical	Scalable	High cost
Hybrid	Mixed design	Flexible	Complex