Cameroon GCE A Level ICT cheat sheet
Cameroon GCE A Level ICT · Keep the key ideas within reach.
Information and Communication Technology - Core Concepts, Systems and Practice
Data vs information: data are raw unprocessed symbols (numbers, characters, signals); information is data processed, organised and contextualised so it reduces uncertainty and supports a decision. Knowledge applies information with experience and rules.
System block model: input → process → output with feedback and a boundary. In ICT, hardware and software are components of an information system whose purpose is to convert data into useful output; a control loop compares output with a standard and adjusts input.
Bit and byte arithmetic: 1 byte = 8 bits; 1 nibble = 4 bits. Decimal prefixes (kilo = 10^3) differ from binary prefixes (kibi = 2^10). 1 KiB = 1024 B, 1 MiB = 1024 KiB, 1 GiB = 1024 MiB. Storage media are usually sold using decimal prefixes, so a '500 GB' drive shows about 465 GiB.
Number systems: binary base 2, octal base 8, denary base 10, hexadecimal base 16 (digits 0-9, A-F). Group binary bits in fours to convert to hex, in threes for octal. Two's complement: invert all bits and add 1 to negate a signed integer; an n-bit two's complement range is -2^(n-1) to 2^(n-1) - 1.
Character coding: ASCII uses 7 bits (128 codes) and is extended to 8 bits (256 codes); Unicode uses variable encodings (UTF-8 uses 1-4 bytes) and covers all world scripts. EBCDIC is an older 8-bit IBM code. A character code maps a symbol to a unique bit pattern.
Von Neumann architecture: CPU (control unit, ALU, registers), main memory, and buses (address, data, control) sharing one memory for instructions and data. The fetch-decode-execute cycle: fetch instruction at the program counter, decode in the control unit, execute in the ALU, store result, increment PC.
CPU performance factors: clock speed (Hz), cores, cache size and levels (L1 fastest, smallest), word length, and instruction pipelining. Throughput is limited by the slowest stage; parallel processing splits a task across cores but adds coordination overhead.
Memory hierarchy and storage: registers → cache → RAM → secondary storage → offline/archival. RAM is volatile and directly addressable; ROM is non-volatile. Magnetic (HDD), optical (CD/DVD/Blu-ray) and solid-state (flash/SSD) media differ in access method (sequential vs direct), capacity, durability and cost per GB.
Software categories: system software (operating system, utilities, translators, device drivers) manages hardware and provides a platform; application software (general-purpose, special-purpose, bespoke) serves end-user tasks. An operating system handles process scheduling, memory management, file management, I/O and security.
Translators: a compiler translates the whole source program into object code before execution and reports all errors at the end; an interpreter translates and executes line by line and stops at the first error; an assembler converts assembly mnemonics to machine code. Compiled code generally runs faster; interpreted code is easier to debug and port.
Programming constructs: sequence, selection (IF/CASE) and iteration (FOR/WHILE/REPEAT). A variable is a named store whose value may change; a constant does not change during execution. Parameters pass data into a procedure or function; a function returns a value, a procedure does not.
Algorithms and pseudocode: an algorithm is a finite, unambiguous sequence of steps that terminates. Standard tools include pseudocode, flowcharts (terminator, process, decision, input/output symbols) and structure diagrams. Dry-run/trace tables test logic by tracking variable values step by step.
Databases and normalisation: a relational database stores data in tables (relations) of rows (records) and columns (fields), linked by primary and foreign keys. Normalisation reduces redundancy: 1NF removes repeating groups, 2NF removes partial dependencies on part of a composite key, 3NF removes transitive dependencies on non-key fields.
SQL essentials: SELECT fields FROM table WHERE condition; ORDER BY sorts, GROUP BY aggregates with COUNT/SUM/AVG, INSERT INTO adds rows, UPDATE ... SET changes rows, DELETE FROM removes rows, JOIN combines tables on a matching key.
Networks: a network links devices to share resources and data. Topologies - star (central switch, single point of failure), bus (shared backbone), ring, mesh (redundant paths). LAN is local and privately owned; WAN spans large distances and often uses leased lines. Client-server centralises control; peer-to-peer shares directly between equals.
Transmission and addressing: serial sends bits one at a time over one channel; parallel sends several simultaneously but suffers skew over distance. Simplex, half-duplex and full-duplex describe direction of flow. An IP address identifies a host on a network; a MAC address is a fixed hardware identifier; DNS resolves domain names to IP addresses; DHCP assigns addresses automatically.
Protocols and the layered model: TCP/IP is the practical suite; the OSI reference model has seven layers (physical, data link, network, transport, session, presentation, application). TCP is connection-oriented and reliable; UDP is connectionless with lower overhead. HTTP/HTTPS, FTP, SMTP, POP3/IMAP and DNS operate at application level.
Security threats and controls: malware types include virus (attaches to a host file), worm (self-replicating over networks), Trojan (disguised as legitimate), spyware and ransomware. Phishing, pharming, social engineering and denial-of-service attacks target people and availability. Controls: strong authentication (something known/possessed/are), firewalls, encryption, access rights, backups, patching and staff training.
Encryption and integrity: symmetric encryption uses one shared key (fast, key-distribution problem); asymmetric uses a public/private key pair (slower, solves key exchange). Hashing produces a fixed-length digest for integrity checking; a digital signature combines a hash with the sender's private key to give authenticity and non-repudiation.
ICT in society and the law: e-commerce models (B2B, B2C, C2C), teleworking, e-learning and e-government change how work is done. Legal and ethical issues include data protection and privacy, copyright and software licensing (proprietary vs open source, freeware, shareware), computer misuse, and the digital divide.
Spreadsheet and data-handling rules: relative references (A1) shift when copied, absolute references ($A$1) do not. Formulas begin with '='; functions include SUM, AVERAGE, IF, COUNTIF, VLOOKUP. Charts chosen by purpose: column/bar for comparison, line for trend over time, pie for proportions of a whole.
System development life cycle: stages are requirements analysis, design, implementation (coding), testing (unit, integration, system, acceptance), deployment and maintenance. Waterfall is sequential with fixed requirements; iterative/agile delivers in increments with user feedback. Validation checks input (range, type, presence, format); verification confirms accuracy (double entry, visual check).