IGCSE ICT Theory Revision (Chapters 1–10)

Chapter 1

Types & Components of Computer Systems

1.1 Hardware & Software

Hardware: Physical, electronic components that make up a computer system.

Internal Hardware: CPU (interprets and executes instructions), Processor, Motherboard (main circuit board), Internal Memory (RAM/ROM), Graphics/Sound cards, Internal Storage (HDD/SSD), Network Interface Card (NIC).
External Hardware: Peripherals such as Monitor, Keyboard, Mouse, Printer, and external storage drives.

Software: Programs, commands, and techniques directing the hardware.

Application Software: Enables users to perform specific tasks. Includes general-purpose (word processors, spreadsheets) and specialist custom software.
System Software: Manages computer resources. Includes Compilers (translates high-level code to machine code), Linkers (combines modules into executable programs), Device Drivers (enables hardware communication), Utilities (antivirus, defragmenters), and Operating Systems (OS).

Analogue vs. Digital Data: Computers process discrete binary signals (0s and 1s), whereas real-world data varies continuously.

ADC (Analogue-to-Digital Converter): Converts continuous physical signals into digital data.
DAC (Digital-to-Analogue Converter): Converts digital signals back to analogue for physical actuators.

1.2 Main Components of Computer Systems

Central Processing Unit (CPU): The core microprocessor containing:
- Control Unit (CU): Directs execution and data flow.
- Arithmetic Logic Unit (ALU): Handles calculations and logical decisions.
- Registers: High-speed internal memory locations.

Memory Type	Volatility	Access	Primary Function
RAM	Volatile (lost on power-off)	Read & Write	Stores active data, running programs, and loaded OS parts.
ROM	Non-Volatile (permanent)	Read-Only	Stores start-up instructions (BIOS) and basic boot firmware.

Internal Memory vs. Backing Storage: RAM is volatile while backing storage is permanent; backing storage has larger capacity and lower cost per GB, but slower data access than internal memory.

1.3 Operating Systems (OS) & User Interfaces

CLI (Command Line Interface): Text-only commands; minimal memory usage, fast for experts, but high learning curve.
GUI (Graphical User Interface): Uses WIMP (Windows, Icons, Menus, Pointer); intuitive and user-friendly, but resource-heavy.
Dialogue-Based: Human voice input; hands-free accessibility, but prone to background noise errors.
Gesture-Based: Sensor/camera detection of body movements without physical contact.

1.4 Types of Computers

Desktop Computers: High performance per cost, easy to upgrade/repair, mains-powered; bulky and not portable.
Laptops: Portable, integrated units; difficult to upgrade, limited battery life, higher risk of theft.
Mobile Devices: Smartphones, Tablets, and Phablets (hybrids bridging phone cellular calls and tablet-sized screens).

1.5 Emerging Technologies

Artificial Intelligence (AI): Machine simulation of human decision-making, diagnostics, and automated workflows.
Extended Reality (XR): Augmented Reality (AR) overlays digital objects onto the real world; Virtual Reality (VR) creates an immersive computer-generated simulated environment.

Chapter 2

Input & Output Devices

2.1 Input Devices

Keyboards & Numeric Keypads: Fast text/numerical input; risk of RSI, slower than direct entry.
Pointing Devices: Mouse, Touchpad, Tracker Ball (ideal for users with RSI or restricted wrist movement).
Touchscreens: Direct selection; versatile but prone to screen smudges and fatigue.
Scanners & Digital Cameras: Digitizes paper documents or captures photos; used with OCR software.
Sensors: Continuous automatic monitoring (Temperature, Pressure, Light, Sound, Humidity, pH). More accurate than humans; require ADCs for computer processing.

2.2 Direct Data Entry (DDE)

Device	Primary Uses	Key Advantage	Key Disadvantage
Magnetic Stripe	ATMs, hotel access cards	Fast, error-free, robust	Data erased by strong magnets
Chip & PIN	Card payment POS	PIN acts as a second security layer	Must shield PIN from view
RFID	Stock/livestock tracking	No line-of-sight required; bulk scan	Radio collision/interference
OMR	MCQ exams, lottery forms	Ultra-fast, accurate marking	Mismarked forms need manual review
OCR / ANPR	Passports, number plates	Converts text into editable data	Struggles with handwriting
Barcodes	Supermarket inventory	Proven, automated stock control	Easily damaged/scratched
QR Codes	URLs, mobile boarding passes	Holds vastly more data than barcodes	Can link to malicious websites

2.3 Output Devices

Monitors: LCD (thin, power-efficient, flicker-free) vs CRT (heavy, bulky, wide viewing angles).
Multimedia Projectors: Large audience presentations; image washed out in bright light.
Printers:
- Laser: High-speed, high-volume, quiet; expensive toner, produces ozone.
- Inkjet: High-quality photo prints, cheap hardware; slow, expensive ink refills.
- Dot Matrix: Multi-part carbon copies; operates in dusty/harsh environments; noisy.
- 3D Printers: Custom prototypes and prosthetics; risk of counterfeit or dangerous items.
Actuators: Motors, buzzers, and valves allowing computers to control physical mechanical hardware (requires DACs).

Chapter 3

Storage Devices & Media

3.1 Backing Up Data

Copying data to a separate medium to protect against hardware failure, accidental deletion, or hacker corruption.

3.2 Data Access Methods

Serial Access: Traverses records sequentially from start to end. Slow; used for batch processing (payroll, utility billing).
Direct Access: Jumps directly to calculate records using key fields. Fast; essential for real-time systems.

3.3 Storage Technologies

Technology	Examples	Mechanisms / Characteristics
Magnetic	HDD, Magnetic Tape	Magnetizes surface bits. High capacity, economical; vulnerable to magnetic fields and mechanical wear.
Optical	CD, DVD, Blu-Ray	Lasers read/burn pits and lands. Blu-Ray uses 405nm blue laser for 5× DVD capacity. Read-only (ROM), write-once (R), rewriteable (RW).
Solid-State	SSD, Pen Drives, SD Cards	Flash memory with zero moving parts. Ultra-fast access (0.1ms), silent, low power; higher cost per GB, finite write endurance.

Chapter 4

Networks & The Effects of Using Them

4.1 Network Devices

NIC (Network Interface Card): Converts data into signals; holds a unique MAC address.
Hub: Broadcasts packets to every port indiscriminately (causes network traffic and security concerns).
Switch: Intelligent hub; inspects packets and routes them solely to the target MAC address.
Router: Transfers packets across distinct networks (e.g., LAN to Internet) using routing tables.
Bridge: Links two local LAN segments using the same protocol.

4.2 Network Architectures & Environments

LAN vs WLAN vs WAN: Local Area Network (single building) vs Wireless LAN (uses WAPs) vs Wide Area Network (geographically dispersed, connects LANs via leased lines/routers).
Internet: Global network of networks. WWW: Interlinked web pages accessed via browsers.
Intranet vs Extranet: Private internal network behind a firewall (Intranet) vs Intranet extended to authorized external partners/clients (Extranet).
Cloud Computing: Remote servers accessed via the internet (Public, Private, Hybrid). Scalable with automatic backups; dependent on stable internet.

4.3 Network Security & Conferencing

Threats: Hacking (unauthorized access), Phishing (fraudulent emails), Pharming (domain redirection to fake sites), Viruses (corrupts files).
Conferencing: Video, Audio, and Web Conferencing reduce international travel expenses and time; impacted by latency and internet stability.

Chapter 5

The Effects of Using IT

5.1 Microprocessor-Controlled Devices

Benefits: Eliminates manual labor, frees up leisure time, enables remote home automation, smart fridges reduce food waste.
Drawbacks: Encourages sedentary habits, causes deskilling, smart appliances introduce IoT security vulnerabilities.

5.2 Health Issues & Ergonomic Solutions

Health Hazard	Causes	Preventative Measure
RSI (Repetitive Strain Injury)	Repetitive keyboard/mouse movements	Ergonomic keyboards, wrist rests, regular breaks
Back / Neck Strain	Prolonged poor posture	Adjustable chairs, tiltable monitors, footrests
Eyestrain & Headaches	Screen glare, screen flicker	Anti-glare filters, proper lighting, LCD monitors
Ozone Irritation	Laser printer emissions in offices	Proper ventilation, dedicated print rooms

Chapter 6

ICT Applications

6.1 Communication & Modelling

Media: Websites (interactive, global), Multimedia presentations, Streaming (buffered media), e-Publications, VoIP (internet audio calls).
Computer Modelling: Software simulations (flood management, structural engineering, finance, weather). Cheaper, safer, and allows scenario testing without real-world risk.

6.2 Automation & Expert Systems

Industrial Robotics: Automated precision manufacturing; operates 24/7 in hazardous conditions; causes assembly-line unemployment.
Expert Systems: AI emulating human expertise (e.g., medical diagnostics, mineral prospecting).
User Interface ⇄ Inference Engine ⇄ [Knowledge Base + Rules Base] ⇄ Explanation System

6.3 Banking & Retail Applications

ATMs: Secure cash withdrawal, PIN authentication, automated fund balance verification.
EFT & EFTPOS: Direct money transfer between bank computers; retail terminals calculate totals and run stock deductions.
Internet Shopping: 24/7 global market access; lacks hands-on inspection, risk of fraud and delayed delivery.
Recognition Systems: ANPR (car plate tracking with OCR), RFID (bulk stock tracking), GPS (satellite routing), GIS (spatial mapping).

Chapter 7

The Systems Life Cycle

1. Analysis ➔ 2. Design ➔ 3. Development & Testing ➔ 4. Implementation ➔ 5. Documentation ➔ 6. Evaluation

7.1 Analysis

Research methods: Observation, Interviews, Questionnaires, Document Review. Produces the Requirements Specification.

7.2 Design & Validation Checks

Designs field structures, screen layouts, and automated validation rules:

Range Check: Data sits between minimum/maximum limits.
Length Check: Matches a predetermined number of characters.
Type / Character Check: Checks correct data type (numeric, alphabetic).
Format Check: Matches set masks (e.g., DD/MM/YYYY).
Presence Check: Ensures fields are not left blank.
Check Digit: Appended digit verifying mathematical accuracy.

7.3 Testing

Normal Data: Expected, valid inputs within range (e.g., 5 for months 1–12).
Extreme Data: Boundary limits of acceptability (e.g., 1 or 12).
Abnormal Data: Invalid inputs outside boundaries or wrong types (e.g., -1, 15, "July").

7.4 System Implementation Methods

Method	Description	Pros / Cons
Direct Changeover	Old stops, new starts immediately.	Fast & cheap; catastrophic risk if it fails.
Parallel Running	Both systems run side-by-side.	Lowest risk, backup available; double workload & costly.
Pilot Running	Introduced to one branch/department first.	Errors isolated to one unit; long organization rollout.
Phased Implementation	Introduced module-by-module gradually.	Gradual training; system integration problems.

7.5 Documentation & Evaluation

Technical Documentation: For maintenance engineers (program code, flowcharts, data structures, validation rules).
User Documentation: For end users (how to run tasks, troubleshooting, error handling, glossary).
Evaluation: Assesses speed, efficiency, usability, and feedback against initial task goals.

Chapter 8

Safety & Security

8.1 Physical Safety Hazards

Electrocution: Liquid spills, damaged wiring. Prevent via circuit breakers and insulation.
Fire: Overloaded wall sockets, blocked vents. Prevent with clear ventilation and CO₂ fire extinguishers.
Trailing Cables: Trip hazards. Tidy via cable ducts and conduit covers.
Falling Equipment: Heavy equipment placed on desk edges. Use large, stable desks.

8.2 Security & Data Protection

Data Protection Principles (e.g., GDPR): Data must be fairly and lawfully processed, limited to necessary purposes, kept accurate, and secured.
Security Measures:
- Encryption: Scrambles data with algorithms; unreadable without decryption keys.
- Firewall: Monitors and filters incoming/outgoing network packets based on security rules.
- SSL / TLS: Encrypts communications between web browsers and secure servers.
- 2FA (Two-Factor Authentication): Requires two independent verification elements (e.g., password + OTP token).

Chapter 9

Audience & Copyright

9.1 Audience Appreciation

Adapting interfaces for target age, technical skill, and accessibility needs (high contrast, screen reader compatibility, voice output).

9.2 Software Copyright & Anti-Piracy

Laws safeguarding software creators against illegal copying, reproduction, or redistribution.

Product Activation Keys: Unique serial keys validated on installation.
Digital Rights Management (DRM): Controls unauthorized playback and distribution.
Cloud Updates: Checks software licensing before issuing patches.

Chapter 10

Communication & Internet Protocols

10.1 Email Communication

Cc vs. Bcc: Carbon Copy (visible recipients) vs. Blind Carbon Copy (recipient addresses kept hidden).
Spam: Unsolicited mass emails; managed via spam filter rules.
Netiquette: Online etiquette (avoiding writing in ALL CAPS shouting and offensive language).

10.2 Internet Architecture & Protocols

URL Architecture: Protocol (https://) ➔ Domain (www.cambridge.org) ➔ Path/Filename (/ict/paper1.html)

Protocol	Full Meaning	Role
HTTP	Hypertext Transfer Protocol	Transmits hypermedia web pages across the internet.
HTTPS	HTTP Secure	Encrypted HTTP session using SSL/TLS encryption.
FTP	File Transfer Protocol	Transfers files directly between clients and remote web servers.
SSL	Secure Sockets Layer	Cryptographic protocol establishing an encrypted web link.