BCS Written ICT key terms

A computer design in which a single memory holds both program instructions and data, and a processor fetches, decodes and executes them one at a time over a shared bus.

The central processing unit executes machine instructions; it contains an arithmetic logic unit for calculations and comparisons, control circuits for sequencing, and registers for temporary storage.

A small, fast memory placed between the processor and main memory that keeps recently or frequently used data close to the CPU to reduce average access time.

Random access memory is the volatile working store of a computer; its contents are lost when power is removed, and any location can be read or written in roughly equal time.

A technique in which the operating system uses disk space to extend apparent main memory, moving inactive pages out and loading needed pages back on demand.

A memory management scheme that divides logical and physical memory into fixed-size blocks called pages and frames, mapping them through a page table so programs need not be contiguous.

A severe performance collapse in which the system spends most of its time swapping pages in and out instead of executing useful work, usually caused by overcommitted memory.

A program in execution with its own address space, program counter, registers and resources; it is the unit of resource ownership and protection in an operating system.

A single sequential flow of execution inside a process that shares the process's memory and open files but keeps its own stack and program counter, allowing cheaper concurrency.

A situation where two or more processes each hold a resource the others need and all wait forever; it requires mutual exclusion, hold-and-wait, no preemption and circular wait together.

A synchronisation variable with an integer value and atomic wait and signal operations, used to control access to shared resources and to coordinate cooperating processes or threads.

A preemptive CPU scheduling policy that gives each ready process a fixed time slice in turn, cycling through the queue so no process starves and response time stays bounded.

Software distributed with source code that anyone may inspect, modify and redistribute under a licence such as the GPL or MIT, often developed collaboratively by a community.

The privileged core of an operating system that manages memory, processes, devices and system calls, running in a protected mode separate from ordinary user programs.

A program that translates an entire source program written in a high-level language into machine code or an intermediate form before it is executed, reporting syntax errors during translation.

A program that reads source code and executes it statement by statement without producing a separate machine-code file, which aids debugging but can be slower than compiled execution.

A seven-layer conceptual framework for network communication, from physical transmission up through data link, network, transport, session, presentation and application layers, used to describe and compare protocols.

The practical four-layer suite underlying the Internet, covering network access, internet, transport and application layers, with IP for addressing and routing and TCP or UDP for transport.

A numeric label assigned to a device on an IP network so packets can be routed to it; IPv4 uses 32 bits in dotted decimal form and IPv6 uses 128 bits.

A bit pattern that separates the network portion of an IP address from the host portion, letting devices decide whether a destination lies on the local network or must be routed elsewhere.

A device that forwards packets between networks by examining destination addresses and consulting a routing table, choosing the best next hop toward the target network.

A transmission method in which data is split into small packets that travel independently and are reassembled at the destination, sharing network capacity efficiently and tolerating link failures.

The Domain Name System is a distributed hierarchical service that translates human-readable domain names into IP addresses, using resolvers, name servers and cached records.

The Hypertext Transfer Protocol is a request-response application protocol in which a client sends methods such as GET or POST to a server, which returns status codes and content.

Hypertext Markup Language describes the structure and content of web pages using elements and attributes, which browsers parse into a document tree for rendering.

Cascading Style Sheets is a language of rules that controls how HTML documents are presented, covering layout, colour, typography and responsive behaviour across screen sizes.

The process of organising relational tables and their dependencies to reduce redundancy and avoid insertion, update and deletion anomalies, typically through first, second and third normal forms.

A column or minimal set of columns whose values uniquely identify each row in a table and may not be null, enforcing entity integrity.

A column or set of columns in one table whose values must match a primary key value in another table, enforcing referential integrity between related records.

Four guarantees of reliable transactions: atomicity means all or nothing, consistency preserves valid states, isolation hides concurrent effects, and durability survives failures once committed.

An attack that inserts malicious SQL fragments through unvalidated user input so the database executes attacker-chosen queries, countered by parameterised queries and input validation.

The reversible transformation of readable data into ciphertext using a key, so that only parties holding the correct key can recover the original information.

A cryptographic value computed over a message with a sender's private key, letting any receiver verify with the public key that the message is authentic and unaltered.

The policies, software and certificate authorities that issue, distribute and revoke digital certificates, binding public keys to verified identities so parties can trust encrypted exchanges.

A network security device or program that inspects traffic and permits or blocks it according to configured rules, separating a trusted internal network from untrusted external networks.

A measure of how an algorithm's running time grows with input size, usually expressed in big-O notation such as O(n log n), ignoring constant factors and hardware details.

An algorithm that finds a value in a sorted array by repeatedly comparing with the middle element and discarding half the remaining range, running in logarithmic time.

A data structure that stores key-value pairs in an array indexed by a hash function, giving average constant-time lookup while needing collision resolution strategies.

The staged process of building software, typically covering requirements gathering, analysis, design, implementation, testing, deployment and maintenance, with models such as waterfall and iterative.

A document stating what a system must do and the constraints it must satisfy, distinguishing functional behaviour from quality attributes such as performance, security and usability.

The Unified Modeling Language is a standard notation for visualising software designs, offering diagrams such as use case, class, sequence and activity diagrams for different views.

The use of information and communication technology to deliver public services, share information with citizens and businesses, and improve the efficiency and transparency of government operations.

The gap between people and regions with reliable access to digital technology and skills and those without, shaped by income, education, geography and infrastructure.

Delivery of computing resources such as servers, storage and software over a network on demand, billed by use and offered as infrastructure, platform or software services.

A branch of artificial intelligence in which algorithms improve their performance on a task by learning patterns from data rather than following only explicitly programmed rules.

A distributed ledger in which transactions are grouped into cryptographically linked blocks replicated across nodes, giving tamper-evident records without a central authority.