NSSCO Computer Studies (6134) key terms

The main processor chip that fetches, decodes and executes program instructions. It contains the control unit, arithmetic logic unit and registers, and its clock speed and core count strongly influence overall computer performance.

The part of the CPU that carries out arithmetic operations such as addition and subtraction and logical comparisons such as AND, OR and NOT. Results are passed to registers or memory under control-unit direction.

The CPU component that directs the fetch-decode-execute cycle by sending control signals to other parts of the processor and to memory and input/output devices, coordinating the timing of every operation.

A very small, very fast storage location inside the CPU used to hold the current instruction, memory addresses or data being processed. Registers are far quicker than cache or RAM but hold very little data.

A design in which program instructions and data share the same memory and travel along the same bus between processor and memory. This simplicity is offset by the bottleneck caused by fetching both over one pathway.

A small, high-speed memory between the CPU and main memory that stores frequently used instructions and data. Accessing cache is much faster than accessing RAM, so a larger cache usually improves performance.

Volatile main memory that holds the operating system, running programs and their data while the computer is switched on. Its contents are lost when power is removed, unlike storage such as a hard disk.

Non-volatile memory whose contents are written during manufacture and normally cannot be changed by the user. It typically stores the bootstrap program that starts the computer and basic firmware instructions.

System software that manages hardware resources, provides a user interface, schedules processes, handles files and memory, and offers services on which application software depends. Examples include Windows, Linux and Android.

System software that performs maintenance tasks such as virus scanning, disk defragmentation, backup and file compression. It supports the computer's health rather than helping the user create documents or other content.

Software stored permanently on a hardware device, often in ROM or flash memory, that controls that device's basic operation. It sits between hardware and higher-level software and can sometimes be updated.

A base-2 number system using only the digits 0 and 1, where each position represents a power of two. Computers use it because electronic circuits can reliably represent two distinct states, such as on and off.

The smallest unit of data in computing, representing a single binary digit, either 0 or 1. Groups of bits form larger units such as bytes, and the number of bits determines how many values can be stored.

A group of eight bits treated as one unit. One byte can store 256 different values, enough for a single character in ASCII, and storage sizes are usually quoted in multiples of bytes.

The base-10 number system used in everyday life, with digits 0 to 9 and each position representing a power of ten. Candidates must convert between denary and binary or hexadecimal values.

A base-16 number system using digits 0-9 and letters A-F. It is widely used as shorthand for binary because one hexadecimal digit represents exactly four bits, making long bit patterns easier to read.

A character coding scheme that assigns a unique numeric code to each letter, digit and symbol, traditionally using seven or eight bits per character. It covers English characters but not most other writing systems.

A character encoding standard that assigns a unique code point to characters in most of the world's writing systems, enabling consistent storage and exchange of multilingual text across different computers and software.

A method of representing signed integers in binary in which the leftmost bit indicates the sign. Negative values are formed by inverting the bits of the positive value and adding one.

An error that occurs when a calculation produces a result too large or too small for the number of bits available to store it, causing the value to wrap around or be flagged as invalid.

A network covering a small geographical area such as a school or office, usually owned and managed by one organisation. It offers high data rates and allows shared devices such as printers and file servers.

A network that spans a large geographical area, connecting sites across cities or countries, often using links leased from telecommunications providers. The internet is the largest example of a WAN.

A network device that forwards data packets between networks by reading destination addresses and choosing the best path. It connects a LAN to the internet and can link separate subnets together.

A unique numeric label assigned to a device on a network so that data packets can be routed to it. IPv4 addresses are 32-bit; IPv6 uses 128 bits to provide far more addresses.

A distributed naming service that translates human-readable domain names into IP addresses so browsers can locate web servers. Without it, users would have to remember numeric addresses.

The full address used to locate a resource on the internet, consisting of a protocol, a domain name and often a path to a specific page or file, for example https://example.com/page.

The protocol used to request and deliver web pages over an encrypted connection, protecting data such as passwords and card details from interception. It is indicated by a padlock in browsers.

The process of converting readable data into an unreadable form using a key, so that only authorised parties can restore it. It protects data during transmission and when stored on devices.

An organised collection of related data stored so that it can be easily accessed, managed and updated. Computerised databases are usually controlled by database management software and structured into tables.

A database in which data is stored in tables of rows and columns, with relationships between tables established by shared key fields. Structured Query Language is commonly used to query such databases.

A field, or combination of fields, that uniquely identifies each record in a table. It must be unique for every row and cannot be left empty, preventing duplicate records.

A field in one table that refers to the primary key of another table, creating a link between the two. It enforces referential integrity by ensuring related records actually exist.

A standard language for creating and manipulating relational databases. Statements such as SELECT, INSERT, UPDATE and DELETE retrieve or change data, often combined with WHERE conditions to filter results.

A finite, ordered set of unambiguous steps that solves a problem or completes a task. Algorithms can be expressed as pseudocode, flowcharts or program code and must terminate after a limited number of steps.

A structured, English-like way of writing an algorithm that uses programming constructs such as IF, WHILE and FOR without the strict syntax of a real language. It is used to plan and communicate solutions.

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

A programming construct that repeats a block of statements, either a fixed number of times with a FOR loop or while a condition remains true with a WHILE loop. It avoids duplicating code.

A programming construct in which a condition is tested and one of several alternative paths is executed, implemented with IF, IF-ELSE or CASE statements. It lets a program respond differently to different inputs.

Software written to damage, disrupt or gain unauthorised access to a computer system. Types include viruses, worms, trojans and ransomware, and protection relies on antivirus software and safe user behaviour.

A social-engineering attack in which fraudulent messages, often emails or fake websites, trick users into revealing passwords, card numbers or other sensitive information by impersonating a trusted organisation.

Legal protection for creations of the mind, such as software, music, images and writing. Copyright, patents and trademarks give owners rights over copying and use, and breaching them can be illegal.

The unauthorised copying, distribution or use of software in breach of its licence. It harms developers, can expose users to malware and is a criminal offence in many countries.