GCE A/L General Information Technology cheat sheet

Data is raw unprocessed facts; information is data processed into a meaningful, decision-useful form; knowledge applies information with experience and judgement.

The IPO (input–process–output) model describes any system: input devices capture data, the CPU processes it, output devices present results; storage holds data between stages.

Hardware is the physical equipment; software is the set of instructions; firmware is software permanently stored in ROM; people and procedures complete an ICT system.

Bit = binary digit (0 or 1); 1 byte = 8 bits; 1 KB = 1024 bytes, 1 MB = 1024 KB, 1 GB = 1024 MB, 1 TB = 1024 GB (binary prefixes).

Data versus information test: information must be accurate, timely, relevant, complete and presented in the right format; raw data need not satisfy these.

ICT convergence means one device (smartphone) combines computing, telephony, camera, GPS and payments; digitisation converts analogue content to binary form.

Bandwidth is capacity of a channel in bits per second; baud rate is signal changes per second; they are equal only when each signal event carries one bit.

The digital divide is the gap between those with effective access to ICT (devices, connectivity, skills) and those without; access alone does not close it.

Von Neumann architecture: CPU (ALU + control unit + registers), memory, input, output; instructions and data share the same memory and bus.

CPU cycle = fetch, decode, execute, store. Clock speed (GHz) sets cycles per second; a core executes one instruction stream, so more cores allow parallel work.

Registers are fastest and smallest: PC (next instruction address), IR (current instruction), MAR (address being accessed), MBR/MDR (data being transferred), ACC (arithmetic result).

Cache (L1/L2/L3) sits between CPU and RAM; it is small, fast and expensive, and exploits locality of reference to reduce average memory access time.

RAM is volatile and holds running programs; ROM is non-volatile and holds firmware/BIOS; cache is volatile and inside or near the CPU.

Secondary storage: HDD uses magnetic platters (cheap per GB, mechanical latency); SSD uses flash memory (faster, shock resistant, limited write cycles); optical uses laser-read pits.

Input devices convert real-world data to digital form (keyboard, scanner, sensor, microphone); output devices convert digital data to human-usable form (monitor, printer, speaker).

Ports and buses: USB is serial hot-swappable; HDMI carries digital video and audio; a bus is a shared set of lines for data, addresses and control signals.

System software (operating system, utilities, device drivers) manages hardware; application software (word processor, browser, spreadsheet) performs user tasks.

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

Multiprogramming keeps several jobs in memory and switches on I/O waits; multitasking time-slices the CPU; multiprocessing uses two or more physical CPUs.

Memory management uses paging (fixed-size frames) and segmentation (variable logical units); virtual memory maps disk space as extended RAM and can cause thrashing.

Scheduling policies: FCFS is simple but suffers convoy effect; SJF minimises average waiting time but risks starvation; round robin gives each process a fixed time quantum.

Open-source software publishes source code for modification and redistribution (e.g. Linux, LibreOffice); proprietary software restricts this; freeware is free of charge but closed.

Utility software performs maintenance: antivirus, backup, disk defragmenter, compression, file manager; a device driver translates OS commands into device-specific signals.

File systems (FAT32, NTFS, ext4) organise directories, file names, permissions and allocation tables; NTFS supports permissions and journalling, FAT32 has a 4 GB file-size limit.

Positional values: binary base 2, octal base 8, decimal base 10, hexadecimal base 16. Hex digit values: A=10, B=11, C=12, D=13, E=14, F=15.

Binary to decimal: sum place values where bits are 1 (1101₂ = 8+4+1 = 13). Decimal to binary: repeated division by 2, read remainders upward.

Group 4 bits = 1 hex digit; group 3 bits = 1 octal digit. Example: 1011 0110₂ = B6₁₆.

Two's complement (n bits): represent −x as 2ⁿ − x, i.e. invert all bits and add 1. Range is −2ⁿ⁻¹ to +2ⁿ⁻¹−1; 8-bit range −128 to +127.

Signed magnitude uses the leftmost bit as sign; it has two zeros (+0 and −0) and a narrower range than two's complement for the same bit count.

ASCII uses 7 bits (128 codes); extended ASCII uses 8 bits (256 codes); Unicode assigns a unique code point per character across all scripts (UTF-8 is variable-length).

BCD encodes each decimal digit in 4 bits (e.g. 59 → 0101 1001); it wastes states and is used in displays and calculators.

Image size in bits = width × height × colour depth; sound file size = sample rate × bit depth × channels × duration (÷8 for bytes).

Logic gates: AND outputs 1 only if all inputs 1; OR outputs 1 if any input 1; NOT inverts; XOR outputs 1 if inputs differ; NAND and NOR are universal gates.

Topologies: star (central switch, single point of failure at hub), bus (shared backbone, collisions), ring (token order), mesh (redundant paths, high cabling cost).

LAN covers a building/campus; MAN a city; WAN a country or globe. The Internet is a network of networks using the TCP/IP protocol suite.

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

IP addresses identify hosts; IPv4 is 32-bit, IPv6 is 128-bit. A subnet mask separates network and host portions; private ranges include 10.0.0.0/8 and 192.168.0.0/16.

TCP is connection-oriented, reliable, ordered, with acknowledgements and retransmission; UDP is connectionless and faster but unreliable - used for streaming and DNS queries.

DNS resolves domain names to IP addresses; DHCP assigns IP configuration automatically; NAT maps private addresses to a public address; ARP maps IP to MAC.

Transmission media: twisted pair (short distance, cheap), coaxial (higher bandwidth than twisted pair), fibre optic (very high bandwidth, immune to EMI), wireless (microwave, Wi-Fi, satellite).

Bandwidth, latency and protocols determine performance; switching forwards frames by MAC within a LAN, routing forwards packets by IP between networks.

A database is an organised collection of related data; a DBMS is software that stores, retrieves, secures and controls concurrent access to it.

Relational model: tables (relations) of rows (tuples/records) and columns (attributes/fields); a primary key uniquely identifies a row; a foreign key references another table's primary key.

Entity integrity: no primary key may be null. Referential integrity: a foreign key value must match an existing primary key or be null.

Normalisation removes redundancy and anomalies: 1NF atomic values; 2NF no partial dependency on part of a composite key; 3NF no transitive dependency on a non-key attribute.

SQL categories: DDL (CREATE, ALTER, DROP), DML (SELECT, INSERT, UPDATE, DELETE), DCL (GRANT, REVOKE), TCL (COMMIT, ROLLBACK).

SELECT … FROM … WHERE filters rows; GROUP BY groups for aggregate functions (COUNT, SUM, AVG, MIN, MAX); HAVING filters groups; ORDER BY sorts results.

Cardinality: one-to-one, one-to-many, many-to-many; a many-to-many relationship is resolved with a junction (link) table holding two foreign keys.

ACID properties: Atomicity (all or nothing), Consistency (valid state to valid state), Isolation (concurrent transactions do not interfere), Durability (committed data survives failure).

Program development life cycle: problem analysis, algorithm/design, coding, testing and debugging, documentation, deployment and maintenance.

Algorithm properties: finite (terminates), definite (unambiguous steps), has input and output, and is effective. A flowchart or pseudocode expresses an algorithm before coding.

Three control structures: sequence, selection (IF…THEN…ELSE, CASE), and iteration (WHILE pre-test, REPEAT…UNTIL post-test, FOR counted loop).

Data types: integer, real/float, character, string, Boolean; a variable is a named memory location whose value can change; a constant does not change during execution.

Sorting: bubble sort repeatedly swaps adjacent items, O(n²); selection sort finds the minimum each pass, O(n²); insertion sort is efficient on nearly sorted data.

Searching: linear search checks each element in turn, O(n) and works on unsorted data; binary search halves the range each step, O(log n), but requires sorted data.

Trace tables record variable values after each step to verify an algorithm by hand; a dry run tests logic without a computer.

Test data types: normal (valid), boundary (at the edge of a range) and invalid/extreme (should be rejected); a syntax error breaks rules, a logic error gives wrong output.

An information system = people + procedures + data + software + hardware; its value depends on supporting decisions, not just storing data.

Transaction processing systems (TPS) record daily routine transactions; management information systems (MIS) summarise them; decision support systems (DSS) model alternatives; executive systems (EIS) present high-level indicators.

e-Commerce models: B2B (business to business), B2C (business to consumer), C2C (consumer to consumer via a platform), G2C (government to citizen e-services).

e-Government services include online tax filing, e-billing, digital identity, land registry and online licence renewal; benefits are speed and transparency, risks are exclusion and data misuse.

e-Learning, e-Health, e-Banking and e-Agriculture are sector e-services; each needs authentication, availability and a trusted payment or record channel.

M-commerce is commerce through mobile devices; mobile wallets and QR payments depend on connectivity, device security and merchant acceptance.

A payment gateway authorises and settles card/online payments; SSL/TLS encrypts the browser–server channel; a digital certificate binds a public key to an identity.

Workflow automation replaces paper routing with electronic approval chains; audit trails record who did what and when, supporting accountability.

Positive social impacts: faster communication, remote work, e-learning access, telemedicine, automation of repetitive work; negative: job displacement, screen addiction, isolation, digital divide.

Intellectual property: copyright protects original expression automatically; patents protect inventions; trademarks protect brand identity; software piracy violates licence terms.

Computer crimes include hacking, phishing, pharming, identity theft, malware distribution, cyberstalking, software piracy and unauthorised data access.

Malware types: virus (attaches to files), worm (self-replicates over networks), Trojan (disguised as legitimate), spyware (collects data), ransomware (encrypts data for payment).

Security goals: confidentiality, integrity, availability (CIA). Controls: authentication (password, OTP, biometrics), access control, encryption, firewall, antivirus, backup and physical security.

Encryption converts plaintext to ciphertext with a key; symmetric uses one shared key (fast, key distribution problem); asymmetric uses a public/private key pair.

Phishing tricks users via deceptive email or sites; pharming redirects via DNS or hosts manipulation; social engineering exploits human trust rather than technical flaws.

Professional ethics for ICT workers: protect user data, avoid conflicts of interest, respect licences, report vulnerabilities responsibly, do not access data without authorisation.

Data protection principles: collect only necessary data, state the purpose, keep it accurate and secure, retain no longer than needed, allow subjects access, do not disclose without consent.