HKDSE ICT key terms

The smallest unit of data in a computer, holding a single binary value of either 0 or 1. Combinations of bits represent all numbers, characters, images and instructions processed by a computer.

A group of eight bits treated as one unit. It commonly stores one ASCII character, and larger quantities of memory or storage are measured in multiples such as kilobytes, megabytes and gigabytes.

A base-2 numeral system using only the digits 0 and 1, where each position represents a power of two. Computers use it because digital circuits have two stable states, on and off.

A base-16 number system using digits 0-9 and letters A-F. It is used as a compact, human-readable shorthand for binary values, for example in memory addresses, colour codes and machine code listings.

A rule that maps characters to numeric codes so a computer can store and exchange text. Common schemes include ASCII for English and Unicode, particularly UTF-8, for multilingual text including Chinese characters.

Automatic checking that input data falls within acceptable rules before processing, such as a range check on age or a format check on a date. It reduces errors but cannot guarantee the data is genuine.

Checking that data has been copied or entered accurately from its source, for example by double entry or visual comparison with the original document. It differs from validation, which checks acceptability rather than accuracy.

An extra digit calculated from the other digits of a code and appended to it. Recalculation later detects common typing errors such as a single wrong digit or two digits swapped.

The component that fetches, decodes and executes program instructions and controls the rest of the computer. Its performance depends on clock speed, number of cores and cache size.

Fast, volatile storage that holds programs and data currently in use by the CPU. RAM loses its contents when power is removed, while ROM retains firmware such as the boot program.

A small, very fast memory between the CPU and main memory that keeps frequently used instructions and data. It reduces average access time, and a larger cache generally improves performance.

The repeating sequence in which the CPU retrieves an instruction from memory, interprets its operation code, carries it out, and then moves to the next instruction. Clock speed determines how many cycles occur per second.

System software that manages hardware, files, memory and processes and provides a user interface. It lets application programs run without dealing directly with hardware details.

Software that performs housekeeping tasks such as file compression, backup, disk defragmentation, antivirus scanning or formatting. Utilities support the system rather than helping users create content.

Reducing file size by encoding data more efficiently. Lossless compression allows exact reconstruction, while lossy compression discards detail, which is acceptable for photos, audio and video.

A picture stored as a grid of pixels, each with a colour value. Quality depends on resolution and colour depth, and enlarging a bitmap reveals individual pixels as visible squares.

An image stored as geometric objects defined by mathematical properties such as coordinates, curves and fill colours. It can be scaled without loss of quality and suits logos and diagrams.

A unique numeric address identifying a device on a network so data can be routed to it. IPv4 uses 32-bit addresses, while IPv6 uses 128-bit addresses to provide far more of them.

A distributed naming service that translates easy-to-remember domain names into IP addresses. Without it, users would have to type numeric addresses to reach websites and mail servers.

The address of a resource on the web, giving the protocol, server name and path, such as https://example.com/page. The browser uses it to request the correct file from the correct server.

An application protocol for transferring web pages in which traffic is encrypted using TLS. It protects confidentiality and integrity, and browsers warn users when a site uses plain HTTP instead.

A method of sending data across a network by splitting it into small packets that travel independently and are reassembled at the destination. It makes efficient shared use of network links.

A device that forwards packets between different networks by reading destination addresses and choosing a path. A home router also typically provides network address translation and wireless access.

An electronic document issued by a trusted authority that binds a public key to an organisation or website. Browsers check it to confirm identity before establishing an encrypted connection.

Converting readable data into ciphertext using an algorithm and a key so that only authorised parties can recover it. Symmetric methods share one key; asymmetric methods use a public and private key pair.

A deception in which attackers send messages that impersonate a trusted party to trick recipients into revealing passwords or payment details, or into opening malicious links and attachments.

Software written to cause harm or gain unauthorised access, including viruses, worms, trojans, ransomware and spyware. Protection relies on updates, cautious behaviour and security software.

A hardware or software filter that examines network traffic and permits or blocks it according to rules. It helps shield a network from unauthorised access but cannot stop every threat.

A named storage location whose value can change while a program runs. It has a data type, a name and a current value, and must usually be declared or initialised before use.

A classification of values that determines what operations are allowed and how much storage is used, such as integer, real, character, string or Boolean. Mixing types may require conversion.

A statement that stores a value into a variable, often written with an equals sign as in total = total + 1. The expression on the right is evaluated first, then the result is placed in the variable.

A control structure in which statements execute one after another in the order written. It is the default flow of a program and is combined with selection and iteration to build algorithms.

A control structure that chooses between alternative paths according to a condition, implemented with if, if-else or case statements. The condition evaluates to true or false.

A control structure that repeats a block of statements, either a fixed number of times with a for loop or while a condition holds with a while loop. It must eventually terminate.

A finite, unambiguous sequence of steps that solves a problem or performs a task for any valid input. It can be expressed as pseudocode or a flowchart before being coded.

A diagram of an algorithm using standard symbols: ovals for start and end, parallelograms for input and output, rectangles for processes and diamonds for decisions, joined by arrows showing flow.

A structured, language-independent description of an algorithm using keywords such as INPUT, IF and WHILE. It is easier to read than real code and can be translated into any programming language.

The gap between people who have effective access to computers, the internet and digital skills and those who do not. It can widen existing inequalities in education, income and opportunity.

Legal rights over creations of the mind, such as copyright, patents and trademarks. Digital copying makes infringement easy, so licensing and lawful use of software and media matter.

The right of individuals to control how information about them is collected, used and shared. It is protected by law and by practices such as consent, minimal collection and secure storage.

Computer systems that perform tasks normally needing human intelligence, such as recognising images, translating text or recommending content. Such systems learn patterns from large amounts of data.

A branch of artificial intelligence in which programs improve at a task by finding patterns in training data rather than following rules written by hand. Output quality depends heavily on the data used.

A network of everyday physical devices fitted with sensors and network connections that collect and exchange data. Examples include smart meters, wearables and home automation, raising security and privacy concerns.