GCE O/L Information & Communication Technology cheat sheet

Data = raw unprocessed facts (e.g., 38, 'K'); Information = processed data with meaning and context (e.g., 'temperature is 38 °C'); Knowledge = information applied to make decisions.

ICT = technologies that capture, store, process, transmit and display data; core components: hardware, software, data, people, procedures, connectivity.

IPO model: Input → Process → Output; Storage is an auxiliary stage holding data between stages.

Hardware categories: input devices, output devices, processing unit (CPU), storage devices, communication devices.

Software categories: system software (OS, utilities, device drivers) and application software (general-purpose, bespoke, off-the-shelf).

Data vs information test: if the value alone is meaningless without context, it is data; if it answers a question, it is information.

ICT in business functions: transaction processing, management information systems, decision support, communication and collaboration.

Emerging ICT trends: cloud computing, IoT, AI, big data, 5G, blockchain - each changes how data is captured, processed or shared.

Von Neumann architecture: CPU (ALU + control unit + registers) fetches instructions and data from the same memory via the fetch-decode-execute cycle.

CPU performance factors: clock speed (GHz), number of cores, cache size, word length (bit width); more cores help multitasking, not single-task speed.

Primary memory: RAM (volatile, read/write, holds running programs) and ROM (non-volatile, read-only, holds firmware/BIOS).

Secondary storage: HDD (magnetic, cheap per GB, moving parts), SSD (flash, faster, no moving parts, more expensive), optical, USB flash, magnetic tape (backup, sequential).

Input devices: keyboard, mouse, scanner, microphone, touchscreen, sensor, barcode reader, webcam; output: monitor, printer (laser/inkjet), speaker, projector, plotter.

Ports and buses: USB, HDMI, Ethernet, Wi-Fi adapter; bus width and clock rate affect data transfer rate.

Memory hierarchy by speed and cost: registers > cache > RAM > SSD > HDD > tape; capacity rises as speed falls.

Power and cooling: PSU wattage must exceed component draw; heat sinks and fans prevent thermal throttling.

Number system bases: binary base 2, octal base 8, decimal base 10, hexadecimal base 16 (digits 0–9, A–F).

Binary to decimal: sum each bit × 2^position (rightmost = 2^0). Decimal to binary: repeated division by 2, read remainders bottom-up.

Hex to binary: replace each hex digit with its 4-bit group (e.g., 2A = 0010 1010); binary to octal: group bits in threes.

1 byte = 8 bits; 1 KB = 1024 bytes (or 1000 in SI marketing), 1 MB = 1024 KB, 1 GB = 1024 MB, 1 TB = 1024 GB.

Unsigned 8-bit range 0–255; signed two's complement 8-bit range −128 to +127; sign bit is leftmost.

Two's complement: invert all bits and add 1 to negate a number; arithmetic overflow occurs when result exceeds the range.

Text encoding: ASCII uses 7 bits (128 characters), extended ASCII 8 bits, Unicode (UTF-8/UTF-16) supports all world scripts.

Image representation: bitmap = pixels × colour depth; file size ≈ width × height × colour depth ÷ 8 bytes; vector graphics store shapes as mathematical objects and scale without pixelation.

Sound: sample rate (Hz) × bit depth × channels × duration = file size; higher rates and depths give better quality but larger files.

Network types by scale: PAN (personal, ~10 m), LAN (building/campus), MAN (city), WAN (country/global); the Internet is the largest WAN.

Topologies: star (central switch, easy fault isolation), bus (single backbone, collision-prone), ring (token passing), mesh (redundant paths, costly).

Transmission media: twisted pair (UTP/STP), coaxial, fibre optic (high bandwidth, immune to EMI), wireless (Wi-Fi, Bluetooth, cellular).

OSI 7 layers: Physical, Data Link, Network, Transport, Session, Presentation, Application; TCP/IP model: Link, Internet, Transport, Application.

IP address identifies a host; IPv4 is 32-bit dotted decimal (e.g., 192.168.1.1), IPv6 is 128-bit hexadecimal; subnet mask separates network and host portions.

DNS resolves domain names to IP addresses; DHCP assigns IP addresses automatically; NAT maps private to public addresses.

Protocols: HTTP/HTTPS (web), FTP (file transfer), SMTP (send mail), POP3/IMAP (receive mail), TCP (reliable, connection-oriented), UDP (fast, connectionless).

Network devices: hub (broadcasts to all ports), switch (forwards by MAC address), router (forwards by IP address between networks), gateway, modem, access point, firewall.

Bandwidth vs latency: bandwidth = data per second (Mbps); latency = delay (ms); throughput is actual achieved rate.

System software controls hardware and provides a platform: operating system, utility programs, device drivers, language translators.

OS functions: process management, memory management, file management, device management, user interface, security and access control.

Application software types: word processing, spreadsheet, database, presentation, graphics, web browser, email, desktop publishing.

Spreadsheet: relative reference (A1) changes when copied, absolute reference ($A$1) stays fixed; functions SUM, AVERAGE, IF, COUNT, MAX, MIN, VLOOKUP.

Word processor features: styles, mail merge, tables, headers/footers, spell check, track changes; templates speed up document creation.

Database package vs spreadsheet: database enforces data types, relationships and queries; spreadsheet is for calculation and quick analysis.

Licensing: proprietary (commercial licence), open source (source code available, often free), freeware (free but closed), shareware (trial then pay).

Utility software: antivirus, backup, disk defragmenter, compression, disk cleanup, firewall.

Database = organised collection of related data; DBMS = software that creates, stores, queries and secures the database.

Relational model: tables (relations) with rows (records/tuples) and columns (fields/attributes); each table needs a primary key.

Keys: primary key uniquely identifies a row; foreign key in one table references the primary key of another, creating a relationship.

Relationship types: one-to-one, one-to-many, many-to-many (resolved with a junction table).

Normalisation reduces redundancy and update anomalies; 1NF removes repeating groups, 2NF removes partial dependencies, 3NF removes transitive dependencies.

SQL basics: SELECT fields FROM table WHERE condition; INSERT, UPDATE, DELETE, CREATE TABLE; ORDER BY sorts, GROUP BY aggregates.

Data validation vs verification: validation checks data is sensible (range, type, presence); verification checks data was copied/entered correctly (double entry, visual check).

Data integrity, backup and access rights (user roles) protect the database; a data dictionary documents fields, types and constraints.

Algorithm = finite, ordered, unambiguous steps solving a problem; represented by pseudocode or flowcharts.

Flowchart symbols: oval = start/end, parallelogram = input/output, rectangle = process, diamond = decision, arrow = flow.

Three control structures: sequence, selection (IF/ELSE, CASE), iteration (FOR, WHILE, REPEAT-UNTIL).

Variables store values in memory; constants do not change; data types: integer, real, Boolean, character, string.

Operators: arithmetic (+, −, *, /, MOD, DIV), relational (=, <>, <, >, <=, >=), logical (AND, OR, NOT).

Sequence of steps: input → process → output; desk-checking traces values through the algorithm to find errors.

Searching: linear search checks each item in turn; binary search halves a sorted list each step (faster but requires sorted data).

Sorting: bubble sort repeatedly swaps adjacent out-of-order items; selection sort finds the minimum each pass.

Validation in programs: range check, type check, length check, presence check, format check.

SDLC phases: analysis → design → development/implementation → testing → deployment → maintenance/evaluation.

Waterfall model: sequential, fixed requirements, documentation-heavy; Agile: iterative sprints, customer feedback, adaptable to change.

Requirements gathering: interviews, questionnaires, observation, document analysis; distinguish functional from non-functional requirements.

Testing levels: unit, integration, system, acceptance; test data types: normal, extreme, abnormal/erroneous.

Business ICT systems: transaction processing (TPS), management information (MIS), decision support (DSS), executive information (EIS), e-commerce, ERP, CRM.

E-commerce models: B2B, B2C, C2C, C2B; benefits include wider market reach, lower overheads; risks include security and fraud.

Business benefits of ICT: automation, faster communication, accurate records, data-driven decisions; costs: hardware, training, maintenance, security.

Changeover methods: direct, parallel, phased, pilot; parallel is safest but costly.

Digital divide: unequal access to ICT due to income, location, education or infrastructure; can widen social inequality.

Social impacts: teleworking, online learning, e-government, social media; risks include cyberbullying, misinformation, screen addiction, job displacement.

Health and safety: RSI, eye strain, back pain; ergonomic chair, monitor at eye level, regular breaks, adequate lighting.

Green ICT: reduce e-waste, recycle hardware, use power-saving settings, virtualisation and cloud to cut energy use.

Ethical issues: privacy, intellectual property, software piracy, plagiarism, digital surveillance, responsible AI use.

Legal frameworks: data protection laws (e.g., GDPR-style rules), computer misuse laws, copyright, freedom of information.

Security threats: malware (virus, worm, trojan, ransomware), phishing, pharming, spyware, denial-of-service, social engineering.

Protection measures: strong passwords, two-factor authentication, encryption, firewall, antivirus, regular backups, access control, user education.

Acceptable use policies and codes of conduct govern workplace and school ICT use.

Cloud computing: on-demand computing over the Internet; service models IaaS (infrastructure), PaaS (platform), SaaS (software); deployment: public, private, hybrid.

Cloud trade-offs: scalability and remote access vs dependence on connectivity, data sovereignty and ongoing subscription cost.

IoT: everyday objects with sensors and network connectivity exchanging data; applications in smart homes, agriculture, health and transport.

Big data: high volume, velocity, variety, veracity, value; analysed with data mining and machine learning to find patterns.

Artificial intelligence: machine learning learns from data, expert systems encode rules, natural language processing handles human language; applications in chatbots, recommendation, diagnosis.

Blockchain: distributed ledger of linked blocks secured by cryptography; underpins cryptocurrencies and smart contracts.

5G and next-gen networks: higher bandwidth, lower latency, more connected devices; enables remote surgery, autonomous vehicles, immersive VR.

AR/VR: AR overlays digital content on the real world; VR immerses the user in a simulated environment; used in training, education and design.

Robotics and automation: programmable machines perform repetitive or hazardous tasks; raises productivity and ethical questions about employment.