8.1 Network and Digital Citizenship

 📘  Notes

Communication & Computer Network

• Communication – Process of sharing ideas, information, feelings between sender and receiver.
• Computer Network – Collection of computers/devices connected to share data, hardware, software, and information.
• Need for Network – Resource sharing saves time and money.
• Data Sharing – Authorized users can access shared databases/files.
• Hardware Sharing – Devices like printers can be shared across network.
• Software Sharing – Programs stored centrally can be accessed by multiple users.
• Electronic Funds Transfer (EFT) – Transfer of money via credit/debit cards, online banking.

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Network Components

• Sender – Device that initiates data transfer.
• Receiver – Device that receives data.
• Communication Channel – Medium (cables, microwave, satellites).
• Protocol – Rules for communication between devices.
• Server – Powerful computer managing files/resources.
• Workstation/Peer – Less powerful computers connected to server.

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Types of Networks

• LAN (Local Area Network) – Small area (home, school, office).
• MAN (Metropolitan Area Network) – Connects LANs across a city/town.
• WAN (Wide Area Network) – Large area, country/world; Internet is the largest WAN.
• PAN (Personal Area Network) – Connects personal devices (phones, laptops) via Bluetooth/Wi-Fi.

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Network Hardware

• Computer – Core device in a network.
• NIC (Network Interface Card) – Provides network access to devices.
• Hub – Central connection point for cables; broadcasts data to all.
• Switch – Forwards data to specific destination; more efficient than hub.
• Router – Connects multiple networks (e.g., LAN to Internet).
• Cables – Twisted pair, coaxial, fiber-optic.
• Resource – Any part of system (disk, printer, memory) usable by programs.

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Communication Channels

• Physical Media – Twisted pair, coaxial, fiber-optic cables.
• Wireless Media – Infrared, broadcast radio, Wi-Fi, cellular radio, microwave, satellites.

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Network Architecture

• Peer-to-Peer Network – All computers equal; best for small networks.
• Client/Server Network – Server provides resources; clients request services.
  • File Server – Stores files.
  • Print Server – Manages printers.
  • Database Server – Stores databases.
  • Network Server – Manages traffic.
  • Web Server – Delivers web pages.

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Network Topology

• Bus Topology – All devices connected to single cable; linear.
• Star Topology – Hub at center; easy to add/remove nodes.
• Ring Topology – Devices connected in circular chain; failure of one affects all.

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Protocols

• HTTP – Transfers web pages.
• FTP – Upload/download files.
• TCP/IP – Standard for Internet communication.
• POP3 – Downloads emails from server (removed after download).
• IMAP – Access emails directly on server (available across devices).
• SMTP – Sends emails across Internet.

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Digital Citizenship

• Definition – Responsible and ethical use of technology.
• Guidelines:
  • Treat others with respect online.
  • Avoid cyberbullying, hate speech, harassment.
  • Protect personal information and privacy.
  • Use strong passwords/security.
  • Respect copyright and intellectual property.

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7.1 Number System (Decimal Binary Octal Hexadecimal)

📖 Notes

1. Number System

• A way to represent numbers in computers.
• Two types:
  • Non‑positional: Symbols have fixed values regardless of position (e.g., tally marks, Roman numerals).
  • Positional: Value depends on position (decimal, binary, octal, hexadecimal).

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2. Decimal Number System (Base 10)

• Uses digits 0–9.
• Place values: powers of 10 (units, tens, hundreds…).
• Example: (123 = 1 x 100 + 2 x 10 + 3 x 1).

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3. Binary Number System (Base 2)

• Uses digits 0 and 1.
• Place values: powers of 2 (1, 2, 4, 8…).
• Example: (1001_2 = 8 + 1 = 9_{10}).
• Bit: Smallest unit (0 or 1).
• Byte: 8 bits grouped together.
• Nibble: 4 bits (half a byte).

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4. Octal Number System (Base 8)

• Digits: 0–7.
• Place values: powers of 8.
• Each octal digit = 3 binary digits.
• Example: (112_8 = 74_{10}).

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5. Hexadecimal Number System (Base 16)

• Digits: 0–9 and A–F (A=10, B=11, C=12, D=13, E=14, F=15).
• Each hex digit = 4 binary digits.
• Compact way to represent binary.
• Example: (4F_{16} = 79_{10}).

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6. Conversions

• Decimal → Binary: Divide by 2, record remainders.
• Binary → Decimal: Multiply digits by powers of 2, add results.
• Decimal → Octal: Divide by 8, record remainders.
• Decimal → Hexadecimal: Divide by 16, record remainders.
• Binary ↔ Octal/Hex: Group bits (3 for octal, 4 for hex).

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7. Important Rules

• Binary numbers: only 0 or 1.
• Octal numbers: digits 0–7.
• Hexadecimal numbers: digits 0–9, A–F.
• Last binary digit = parity check (0 = even, 1 = odd).
• Zero power rule: any number raised to power 0 = 1.

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6.1 Malware - Threat to computers

 

Notes

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🦠 Malware

• Definition: Malicious software that acts without user’s knowledge and alters computer operations.
• Payload: The destructive event malware is designed to deliver.
• Symptoms: Slow performance, full storage, unusual messages, system property changes, unexpected shutdowns.

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🧩 Types of Malware

• Virus: Program written to damage data; attaches to files and activates on certain events.
• Worm: Self-replicating malware that consumes system resources.
• Trojan Horse: Disguised as a friendly program but destroys data.
• Rootkit: Hides in a computer, allows remote control.
• Logic Bomb: Dormant until triggered by a specific date/event.
• Adware: Displays unwanted ads, may lead to infected sites.
• Spyware: Secretly collects user information.
• Keyloggers: Record keystrokes to steal sensitive data.
• Ransomware: Locks system and demands payment to restore access.

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🧬 Types of Viruses

• File Infector: Infects program files, spreads when executed.
• Boot Sector Virus: Attaches to boot sector, very dangerous.
• Macro Virus: Infects files with macros (automated tasks).
• E-mail Virus: Spreads via infected email attachments.
• Executable File Virus: Infects executable (.exe) files.

Examples:

• Sweeper: Fake antivirus that changes system files.
• Sleeper: Steals personal/financial info, targets large networks.
• Alabama: Infects executable files, manipulates file names.

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📥 Sources of Viruses

• E-mail attachments
• Internet downloads
• Software distribution via infected media

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🛡️ Antivirus Programs

• Definition: Detect and remove viruses; use virus signatures (patterns of virus code).
• Working: Infected files are removed or quarantined (isolated).
• Virus Hoax: Fake warnings about non-existent viruses.

Popular Antivirus Software: Norton, McAfee, Kaspersky, AVG, TotalAV, Quick Heal.

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⚠️ Precautions Against Malware

• Do not boot with removable media inserted.
• Avoid opening unexpected email attachments.
• Verify attachments even from known contacts.
• Delete suspicious messages.
• Never share sensitive data via email.
• Download only from trusted websites.
• Install and update antivirus regularly.
• Scan all downloads before use.

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