HKDSE ICT flashcards

33 cards. Read the term and the definition here. The deck at the top of this page is optional.

Data versus information

Data are raw, unprocessed facts such as numbers or characters. Information is data that has been processed and organized into a meaningful form useful for decision-making.

Byte and bit

A bit is a single binary digit, 0 or 1. A byte is a group of 8 bits and typically stores one character in extended ASCII coding.

Two's complement

A method of representing signed integers in binary. Invert all bits of the positive value and add 1 to get the negative; an n-bit range is −2^(n−1) to 2^(n−1)−1.

Lossy versus lossless compression

Lossless compression such as ZIP or PNG restores the exact original data. Lossy compression such as JPEG or MP3 permanently discards detail to achieve a much smaller file size.

Validation versus verification

Validation checks that input meets preset rules of format, range, type or presence. Verification checks that data accurately matches the source, for example by double entry.

Hexadecimal conversion

Each hexadecimal digit represents four binary bits. Convert binary to hex by grouping bits in fours from the right, then mapping 0000-1111 to 0-9 and A-F.

CPU components

The control unit fetches and decodes instructions and coordinates the machine cycle. The arithmetic logic unit performs arithmetic and logical operations. Registers hold the data and addresses currently in use.

RAM versus ROM

RAM is volatile read-write main memory holding programs and data while running, losing contents when power is off. ROM is non-volatile, read-only memory storing bootstrap firmware.

Cache memory

A small, very fast memory between the CPU and main memory that holds recently or frequently used data. A higher cache hit rate reduces average access time.

Von Neumann architecture

A design in which program instructions and data share the same main memory and bus. Instructions are fetched, decoded and executed sequentially by the CPU.

Operating system functions

An operating system manages processes and scheduling, allocates memory, organizes files, controls input and output devices, provides a user interface and enforces access control.

Solid-state drive

Secondary storage using flash memory with no moving parts. It offers faster random access, lower power use and greater shock resistance than a magnetic hard disk, usually at higher cost per gigabyte.

Machine cycle

The repeated sequence of fetch, decode, execute and store by which the CPU runs instructions. Clock speed in hertz determines how many cycles occur per second.

DNS

The Domain Name System translates human-readable domain names into numeric IP addresses so that browsers can locate servers on the Internet.

IPv4 versus IPv6

IPv4 addresses are 32 bits written as four decimal octets. IPv6 addresses are 128 bits written in hexadecimal groups, providing a vastly larger address space.

TCP versus UDP

TCP is connection-oriented and reliable, retransmitting lost packets, so it suits web and file transfer. UDP is connectionless and faster but unreliable, suiting streaming and voice.

LAN versus WAN

A local area network covers a small area such as one building under a single administration. A wide area network spans large distances and links networks, often using public carriers.

Search engine operators

Quotation marks search an exact phrase, a minus sign excludes a term, site: restricts results to one domain, and filetype: restricts results to a specified file format.

Packet switching

A message is divided into packets that travel independently across the network by different routes and are reassembled in order at the destination.

HTTPS

A web protocol that encrypts traffic between browser and server using TLS. It protects transmitted data such as passwords and payment details from interception.

URL structure

A URL gives protocol, domain name, path and optional query string, for example https://site.com/page?q=1. The protocol states how the resource is accessed.

Iteration structures

A for loop repeats a known number of times. A while loop tests its condition before each iteration and may run zero times. A do-while tests after the body.

Pass by value

A parameter-passing method in which the subroutine receives a copy of the argument. Changes made inside the subroutine do not affect the caller's original variable.

MOD and integer division

MOD returns the remainder after division, while integer division returns the whole-number quotient discarding any fraction. Both are used for divisibility tests and digit extraction.

Logic error

An error in which the program runs without crashing but produces incorrect output because the algorithm or logic is wrong. It is found by testing and tracing.

Function versus procedure

A function returns a value to the caller through a return statement and can be used inside an expression. A procedure performs actions without returning a value.

Boolean data type

A data type with only two possible values, true and false. It typically stores the result of a comparison or logical expression used in selection and iteration.

Digital divide

The gap between people who have effective access to devices, connectivity and digital skills and those who do not, driven by income, age, location and education.

Ransomware

Malicious software that encrypts a victim's files or locks the system and demands payment for restoration. Regular offline backups reduce the impact.

Phishing

A deception in which fake messages or websites imitate a trusted organization to trick users into revealing passwords, card numbers or other sensitive data.

Green computing

Practices that reduce the environmental impact of computing, including power management, virtualization, device recycling, duplex printing and extending hardware life to cut e-waste.

Cloud service models

IaaS supplies virtual infrastructure, PaaS supplies a development platform, and SaaS supplies ready-to-use applications. All are typically pay-per-use and scalable over the Internet.

AI hallucination

A generative AI output that is fluent and confident but factually wrong or fabricated. It arises because the model predicts plausible text rather than verifying facts, so human checking is required.