Cambridge IGCSE Computer Science 0478 Paper 1 Practice Flashcards

Comprehensive practice vocabulary flashcards covering the Cambridge IGCSE Computer Science 0478 Paper 1 syllabus.

Binary (Base 2)

A number system using only the digits $0$ and $1$. All computer data is represented in binary because transistors have two physical states — on ($1$) and off ($0$).

Denary (Base 10)

The standard human number system using digits $0$-$9$. Also called decimal.

Hexadecimal (Base 16)

A number system using $16$ symbols: $0$-$9$ and $A$-$F$. One hex digit represents exactly one nibble ($4$ bits). Used in MAC addresses, HTML colour codes, memory addresses, and error codes.

Bit

Smallest unit of data; either $0$ or $1$.

Nibble

$4$ bits. One hexadecimal digit.

Byte

$8$ bits. The basic unit of data storage.

Binary left shift

Multiplies integer by $2$ per position shifted left. Bits shifted off the left end are permanently lost; zeros fill the right end.

Binary right shift

Divides integer by $2$ (integer division) per position shifted right. Bits shifted off the right end are permanently lost; zeros fill the left.

Overflow error

Occurs when binary addition result exceeds the register capacity — e.g., greater than $255$ in an $8$-bit register. The carry out of the MSB position signals overflow.

Two's complement

Method for representing positive and negative integers in binary. To negate: invert all bits, then add $1$. MSB = $-128$ in $8$-bit. Range: $-128$ to $+127$.

ASCII

American Standard Code for Information Interchange. $7$-bit encoding (extended: $8$-bit). Represents English letters, digits, and basic symbols. 'A' = decimal $65$.

Unicode

International character encoding supporting all world languages, symbols, and emoji. Uses more bits per character than ASCII (UTF-8: $8$–$32$ bits). Superset of ASCII.

Sample rate

Number of audio samples taken per second ($Hz$). Higher rate $\rightarrow$ more accurate reproduction $\rightarrow$ larger file size.

Sample resolution

Number of bits per audio sample. Higher resolution $\rightarrow$ greater dynamic range $\rightarrow$ larger file size.

Pixel

Smallest addressable element in a digital image. Stores colour as a binary value.

Resolution (image)

Total number of pixels in an image ($\text{width} \times \text{height}$). Higher resolution $\rightarrow$ more detail $\rightarrow$ larger file size.

Colour depth

Number of bits per pixel representing colour. $1$ bit = $2$ colours; $8$ bits = $256$ colours; $24$ bits = $16.7$ million colours.

Lossy compression

Reduces file size by permanently removing data. Cannot restore original quality. Examples: JPEG, MP3.

Lossless compression

Reduces file size without any permanent data loss. Original can be perfectly reconstructed. Example: run-length encoding (RLE). Used in PNG, FLAC, ZIP.

Run-length encoding (RLE)

Lossless compression: replaces consecutive repeated values with a count and the value. E.g., AAAABBB $\rightarrow$ 4A3B.

Image file size formula

$\text{File size (bits)} = \text{width (px)} \times \text{height (px)} \times \text{colour depth (bits/px)}$. Always divide by $1024$ to convert to KiB or MiB.

Sound file size formula

$\text{File size (bits)} = \text{sample rate (Hz)} \times \text{sample resolution (bits/sample)} \times \text{duration (seconds)}$.

Packet

Fixed-size unit of transmitted data. Structure: header + payload + trailer.

Packet switching

Data broken into packets that may take different routes; routers manage routing; packets may arrive out of order; receiver reassembles using packet numbers.

Router

Forwards packets between networks by examining destination IP addresses and determining optimal routes.

Serial transmission

Bits sent one at a time along a single wire. Reliable over long distances. Used in USB.

Parallel transmission

Multiple bits sent simultaneously along multiple wires. Faster over short distances; synchronisation issues over long distances.

Simplex

Data transmission in one direction only (e.g., keyboard to computer).

Half-duplex

Data transmission in both directions but only one at a time (e.g., walkie-talkie).

Full-duplex

Data transmission in both directions simultaneously (e.g., telephone call, internet connection).

USB (Universal Serial Bus)

Standard peripheral interface using serial transmission. Benefits: plug-and-play, hot-swappable, powers device, universal compatibility.

Parity check

Parity bit added to make total $1$s even (even parity) or odd (odd parity). Detects single-bit errors; cannot detect double-bit errors; cannot correct errors.

Checksum

Value calculated from data before and after transmission; if values differ, an error occurred.

Echo check

Received data sent back to sender for direct comparison with the original.

Check digit

Digit appended to a data string; calculated using a formula; detects data entry errors. Used in ISBN-13 and EAN barcodes.

ARQ (Automatic Repeat Query)

Receiver sends ACK (correct) or NACK (error). If no ACK within timeout, sender retransmits. Provides error correction.

Symmetric encryption

One shared key for both encryption and decryption. Fast. Key distribution problem — securely sharing the key is difficult.

Asymmetric encryption

Public key (shared freely) encrypts; private key (never shared) decrypts. Eliminates key distribution problem. Slower than symmetric.

CPU (Central Processing Unit)

Main processing component. Fetches, decodes, and executes program instructions. Consists of ALU, CU, registers, and buses.

Microprocessor

A processor implemented as a single integrated circuit on one chip.

ALU (Arithmetic Logic Unit)

Performs arithmetic operations (add, subtract) and logical operations (AND, OR, NOT, compare).

CU (Control Unit)

Manages all CPU operations; sends control signals; coordinates the FDE cycle.

Program Counter (PC)

Holds the address of the NEXT instruction to be fetched. Automatically incremented after each fetch.

Memory Address Register (MAR)

Holds the memory address currently being accessed (read from or written to).

Memory Data Register (MDR)

Temporarily holds data or instruction just fetched / about to be written to memory. Acts as CPU-RAM buffer.

Current Instruction Register (CIR)

Holds the instruction currently being decoded and executed.

Accumulator (ACC)

Stores results of arithmetic and logical operations from the ALU.

Address bus

Unidirectional — carries memory addresses from CPU to memory and peripherals.

Data bus

Bidirectional — carries data and instructions between CPU, memory, and peripherals.

Control bus

Carries control signals from the CU to all components to coordinate operations.

FDE Cycle

Fetch: PC$\rightarrow$MAR; instruction$\rightarrow$MDR; MDR$\rightarrow$CIR; PC incremented. Decode: CU decodes CIR instruction. Execute: ALU operates; result$\rightarrow$ACC; or data transfer.

Cache

Very fast memory adjacent to CPU. Stores frequently used instructions and data to reduce slow RAM accesses. L1 is fastest and smallest.

Clock speed

Rate of CPU cycle completion in $GHz$. Higher speed = more instructions per second.

Core

Independent processing unit within one CPU chip. Multi-core enables parallel execution.

Embedded system

Computer with fixed, dedicated function built into a larger device. Contrast with general-purpose computer.

RAM

Volatile primary storage. Holds data and programs currently in use. Data lost when power is removed.

ROM

Non-volatile primary storage. Holds firmware/BIOS. Read-only; retains data without power.

Virtual memory

Section of secondary storage used as RAM extension when RAM is full. Pages swapped between RAM and secondary; significantly slower than RAM.

HDD

Magnetic storage: platters, tracks, sectors; read/write using electromagnets. Slow; fragile (moving parts); high capacity; cheap per GB.

SSD

Flash memory: NAND/NOR transistors as control and floating gates. Fast; silent; durable; no moving parts; expensive per GB.

Optical storage

Laser reads pits and lands on disc surfaces. Examples: CD, DVD, Blu-ray. Portable; cheap; easily scratched; slow.

Cloud storage

Remote storage on servers accessed via internet. Any-location access; scalable; requires internet; third-party security risk.

MAC address

Unique $48$-bit hardware identifier assigned at manufacture to a NIC. Written in hexadecimal. Structure: manufacturer code ($24$ bits) + serial code ($24$ bits).

IP address

Logical network address; assigned by network; static or dynamic. Used for internet routing.

IPv4

$32$-bit logical network address.

IPv6

$128$-bit logical network address.

System software

Software providing the services required by the computer hardware — includes OS and utility software.

Application software

Software providing services the user requires to complete specific tasks.

Operating system

System software managing hardware resources and providing a platform for applications. Performs $8$ functions including file, memory, and multitasking management.

Interrupt

Signal to CPU requesting immediate attention. Handled by an Interrupt Service Routine (ISR).

High-level language

Human-readable, machine-independent language (e.g., Python, Java). Easy to read/write/debug; portable; must be translated.

Low-level language

Language close to machine code: assembly or machine code. Machine-specific; direct hardware control; efficient; hard to read.

Machine code

Binary instructions executed directly by CPU without translation.

Assembly language

Low-level language using mnemonics (ADD, MOV). Assembler translates to machine code. One-to-one instruction correspondence.

Compiler

Translates whole high-level program before execution; produces executable file; reports all errors at end; faster execution.

Interpreter

Translates and executes line by line; stops at first error; no executable produced; slower; used during development.

IDE

Integrated Development Environment. Features: code editor, translator, error diagnostics, auto-completion, auto-correction, prettyprint.

Internet

Global physical infrastructure of interconnected networks — cables, routers, servers. The infrastructure layer.

World Wide Web (WWW)

Collection of websites and web pages accessed using the internet via browsers. NOT the same as the internet.

URL

Text-based address for a web page. Components: protocol (https://), domain name, optional file path.

HTTP

HyperText Transfer Protocol. Transmits web pages unencrypted. Not for sensitive data.

HTTPS

HTTP + SSL/TLS encryption. Used for login pages, banking, e-commerce — any sensitive data transmission.

DNS (Domain Name Server)

Translates domain names to IP addresses. Required because internet routing uses IP addresses, not domain names.

Cookie

Small data file stored on user's device. Uses: login state, preferences, shopping cart.

Digital currency

Currency existing only electronically (e.g., Bitcoin). Decentralised; recorded using blockchain.

Blockchain

Distributed digital ledger: immutable, time-stamped chain of records. Each block cryptographically linked to the previous.

Brute-force attack

Automated systematic trial of all possible passwords or keys until correct one is found.

Phishing

Fraudulent communications appearing to come from a trusted source. Designed to steal credentials or install malware.

Pharming

Corrupts DNS records or hosts file to silently redirect users from legitimate to fraudulent sites.

DDoS attack

Botnet sends mass simultaneous requests to target server, overwhelming it and denying service to legitimate users.

Virus

Malware attaching to files; spreads when files are shared; executes when host file is opened.

Worm

Self-replicating malware spreading autonomously across networks; no host file needed.

Trojan horse

Malware disguised as legitimate software; installed willingly; creates backdoors or steals data.

Ransomware

Encrypts victim's files with key held only by attacker; demands payment for decryption key.

Social engineering

Psychological manipulation to reveal confidential information or grant access. Exploits trust, not technical vulnerabilities.

Firewall

Hardware or software filtering network traffic based on security rules. Blocks unauthorised connections.

SSL

Secure Socket Layer. Encryption protocol securing client-server data transmission. Used in HTTPS.

Two-step verification

Authentication requiring two factors: knowledge (password) + possession (phone/token) or biometric.

Proxy server

Intermediary server processing requests between client and internet. Provides anonymity and content filtering.

Automated system

System operating without direct human intervention using sensors (input), microprocessor (processing), and actuators (output).