A Level Computer Science Paper 3/4 Complete Review Notes

Vocabulary-style flashcards covering Paper 1 components of the A Level Computer Science syllabus including hardware, networking, system software, and databases.

BCD (Binary Coded Decimal)

A way to represent denary digits where it is more straightforward to convert between denary, easier for digital equipment to display information, and can represent monetary values exactly.

Character Set

All of the characters that the computer can represent or use, where each character has a corresponding unique binary number.

Unicode

A character set that can represent multiple languages and a wider range of characters than ASCII, typically using $16bit$ codes.

Bitmap Graphic

An image made up of pixels, each of a single colour with a unique binary value, stored as a sequence of binary numbers.

Pixel

The smallest addressable element in an image.

File header

Stores metadata about a bitmap image, such as file type, compression type, dimensions (width $\times$ height), and colour depth.

Image Resolution

The total number of pixels in an image, calculated as the number of pixels wide multiplied by the number of pixels high.

Bit depth / Colour depth

The number of bits used to represent each colour or the number of bits per pixel, which determines the number of colours that can be represented.

Vector Graphic

An image type that stores a set of instructions about how to draw shapes, which does not pixelate when scaled and usually has a smaller file size.

Drawing Object

A component of a vector graphic created using a formula or command.

Drawing List

A list of all drawing objects in an image and the commands required to draw each object.

Sampling

The process of taking measurements of sound amplitude at regular intervals and storing the values as unique binary numbers.

Sampling Rate

The number of samples taken per unit time or per second ($Hz$).

Sampling Resolution

The number of bits used to store each sound sample, determining the range of amplitudes that can be represented.

Analogue data

A variable or data value that is constantly changing.

Lossy Compression

A compression method where original data is lost or deleted and the file cannot be reconstructed to its original state.

Lossless Compression

A compression method where the original data is preserved, allowing the file to be fully restored.

Run-length Encoding (RLE)

A lossless compression technique that identifies sequences of repeated characters/pixels and replaces them with a copy of the character and the count of occurrences.

LAN (Local Area Network)

A network covering a small geographical area with infrastructure typically privately owned, supporting high data transfer rates.

WAN (Wide Area Network)

A network covering a large geographical area, often virtual connections with lower data transfer rates, likely controlled by external organisations.

Client-Server Model

A network model where a client sends requests to a server, which processes tasks and returns results (e.g., web servers hosting shared files).

Peer-to-peer network

A network where computers are of equal status, data is distributed, and each computer is responsible for its own security.

Thick-Client

A client-server setup where the server performs minimal processing and most resources are installed locally on the client.

Thin-Client

A client-server setup where the server performs all processing and data storage, and the client only sends requests and displays results.

Star Topology

A network layout where all devices are connected to a central router, switch, or hub.

Mesh Topology

A network layout where all computers are connected to at least one other device, allowing multiple routes and data relaying.

Cloud Computing

Accessing files or services on a remote server via the internet.

Switch

Hardware that allows communication between devices on a network by receiving transmissions and forwarding them directly to their destination.

WNIC (Wireless Network Interface Card)

Provides an interface to a wireless network, converts between analogue radio waves and digital data, and provides a MAC address.

WAP (Wireless Access Point)

Hardware providing radio communication (Wi-Fi) from a central device to nodes, allowing wireless devices to connect to a wired network.

Bridge

A device that connects two LANs that use the same protocol.

Repeater

A device that restores a digital signal so it can be transmitted over greater distances.

Router

A device that routes packets to destinations using IP addresses, maintains a routing table, and finds the most efficient path.

CSMA/CD (Carrier Sense Multiple Access with Collision Detection)

A protocol used to detect and prevent collisions by listening to a channel and waiting a random time to retransmit if a collision is detected.

Bit Streaming

A method where compressed video/audio is transmitted continuously as a series of bits into a buffer on the client computer.

PSTN (Public Switched Telephone Network)

A network of communication lines using switching centres to provide dedicated channels for full duplex data transmission.

IPv4

An IP address format consisting of $4$ groups of $8$ bits ($32bit$) separated by full stops.

IPv6

An IP address format consisting of $8$ groups of $16$ bits ($128bit$) separated by colons.

Subnetting

Dividing a network into smaller sub-networks using network IDs and host IDs to improve security and reduce traffic.

DNS (Domain Name System)

A system with a database of domain names and corresponding IP addresses used to resolve URLs entered into a browser.

Embedded system

A microprocessor within a larger system (like a washing machine) designed for a specific task, combining hardware and software without a full operating system.

Actuator

A component that converts electrical energy into mechanical energy to produce a physical action.

Stored Program Concept

The principle that instructions and data are stored in the same memory space or in main memory.

Program Counter (PC)

A special purpose register that holds the address of the next instruction to be loaded.

MAR (Memory Address Register)

A register that stores the address of the memory location currently being read from or written to.

MDR (Memory Data Register)

A register that holds the data fetched from memory or data waiting to be written to memory.

CIR (Current Instruction Register)

A register that holds the instruction currently being decoded or executed.

Control Unit (CU)

Component of the CPU that synchronises actions using the system clock and manages the execution of instructions.

Buses

Communication channels in the CPU: Address bus (carries addresses), Data bus (carries data), and Control bus (carries signals like read/write).

Interrupt

A signal sent from a device or process seeking the attention of the processor.

ISR (Interrupt Service Routine)

A specific program or set of instructions called to handle a particular interrupt.

Register Transfer Notation (RTN)

A way to describe the stages of the Fetch-Execute cycle, e.g., MAR $\leftarrow$ [PC].

Two-Pass Assembler

A translator for assembly language that creates a symbol table in the first pass and generates machine code in the second pass.

Direct Addressing

An addressing mode where the operand holds the memory address of the data.

Indexed Addressing

An addressing mode where the address is formed by adding the operand address to the contents of the Index Register.

Bit Masking

Using logic gates ($AND$, $OR$, $XOR$) to check, set, or clear specific bits in a register.

Memory Management

OS task that controls data movement between RAM and the processor, and allocates RAM blocks to processes.

Process Management

OS task that manages the scheduling of processes and handling of the process queue for multitasking.

Defragmentation

Utility software that rearranges blocks of files to be contiguous in memory to improve disk access times.

Compiler

A translator that converts high-level language into an executable machine code file all at once.

Interpreter

A translator that converts high-level language into machine code line by line at runtime.

Digital signature

A security measure where a message digest is encrypted with a sender's private key to ensure authenticity.

Firewall

Security software or hardware that accepts or rejects incoming/outgoing packets based on user-defined criteria.

Phishing

An internet threat where an email pretending to be from an official body persuades individuals to disclose private information.

Pharming

An internet threat that automatically redirects a user to a false or fake website.

Validation

A check to ensure data is reasonable or sensible (e.g., format check, length check).

Verification

A check to ensure data matches the original source (e.g., visual check, double entry).

Checksum

An error detection value calculated from data before transmission and recalculated by the receiver to check for errors.

Shareware

Software that is copyrighted and provides a free trial period, but users cannot legally modify or redistribute it.

Data Dictionary

A file containing metadata about a database, such as table names, field names, data types, and validation rules.

Referential Integrity

A database rule ensuring that every foreign key has a corresponding primary key and that records are not modified incorrectly.

Normalisation

The process of organising data in a database to reduce redundancy and improve data integrity (stages include $1NF$, $2NF$, and $3NF$).