AQA GCSE Computer science

What are the three number bases you must know?

Decimal (Base 10: 0-9), Binary (Base 2: 0-1), and Hexadecimal (Base 16: 0-F).

Why do computers use binary?

Computers are made of transistors that act like tiny switches, which can only be in two states: ON (1) or OFF (0).

Why do computer scientists use Hexadecimal if computers only read binary?

It is much easier for humans to read, write, and debug, taking up fewer characters on screen and reducing human error.

What are the maximum values you need to know for 8 bits?

Decimal: 255, Binary: 1111 1111, Hexadecimal: FF.

What is the difference between a bit and a byte?

A bit (b) is a single 0 or 1 (smallest unit of data). A byte (B) is a group of 8 bits.

What are the 4 data storage prefixes in order?

Kilo (kB) = 1,000 bytes; Mega (MB) = 1,000 kB; Giga (GB) = 1,000 MB; Tera (TB) = 1,000 GB. (AQA uses 1,000, not 1,024).

What is the maximum number of bits and numbers you will be asked to add together in binary?

A maximum of 3 binary numbers, up to 8 bits each.

What does a logical binary shift do?

A left shift multiplies a number by powers of 2. A right shift divides a number by powers of 2.

What is a character set?

A look-up table that links a binary number to a text character so the computer can display it.

What is the difference between ASCII and Unicode?

ASCII is 7-bit (128 English characters, small file size). Unicode stores millions of characters (all languages/emojis, larger file size).

What is a pixel?

Short for "picture element"—the smallest single point of color in a bitmap image.

What is Colour Depth?

The number of bits used to represent the color of a single pixel. More bits = more unique colors available.

How do you calculate Bitmap Image File Size?

In bits: Width x Height x Colour Depth. In bytes: (Width x Height x Colour Depth) ÷ 8.

How is sound converted from analogue to digital?

The amplitude (height) of the continuous sound wave is sampled (measured) at regular time intervals and converted into binary numbers.

What are Sample Rate and Sample Resolution?

Sample Rate is the number of samples taken per second (Hertz, Hz). Sample Resolution is the number of bits used to store each individual sample.

How do you calculate Sound File Size?

File Size (bits) = Sample Rate x Sample Resolution x Duration (seconds).

What is Run-Length Encoding (RLE)?

Data compression that reduces file size by grouping repeating data items into a frequency/data pair (e.g., 00000 becomes 5 0).

What is the difference between hardware and software?

Hardware is the physical parts you can touch (CPU, RAM). Software is the digital programs and instructions executed by the hardware.

What are the 4 logic gates you need to know?

NOT (inverts input), AND (both must be 1), OR (either can be 1), and XOR (exclusively one or the other must be 1).

What are the Boolean algebra symbols for the gates?

AND: . (dot), OR: + (plus), XOR: ⊕ (circle plus), NOT: overbar above the letter.

What is the difference between System Software and Application Software?

System Software manages computer resources and provides a platform (OS, Utilities). Application Software lets the user complete specific tasks (browsers, games).

What 5 core resources does an Operating System (OS) manage?

Processor(s), Memory, Input/Output (I/O) devices, Applications, and Security.

What is the difference between High-Level and Low-Level programming languages?

High-Level is human-readable (Python), needs translating, and is portable. Low-Level is machine-readable (Assembly/Machine code), hardware-specific, and runs very fast.

What are the 3 types of program translators?

Compiler (translates all at once into executable), Interpreter (translates/runs line-by-line), Assembler (translates Assembly 1:1 into Machine Code).

What are the components of a Von Neumann CPU?

ALU (Arithmetic Logic Unit), CU (Control Unit), Clock, Registers, and Buses.

What 3 factors affect CPU performance?

Clock speed (cycles per second), number of processor cores (independent units), and cache size (super-fast memory near the CPU).

What happens during the Fetch-Decode-Execute cycle?

Fetch: Retrieves next instruction from RAM. Decode: Control Unit interprets the instruction. Execute: CPU carries out the instruction.

What is the difference between RAM and ROM?

RAM is volatile (loses data when off), holds active programs, and is read/write. ROM is non-volatile, holds boot-up instructions (BIOS), and is read-only.

Why do computers need secondary storage?

Because main memory (RAM) is volatile, so secondary storage is needed to permanently save files and software when powered off.

What are the 3 types of secondary storage media?

Solid State (SSD: electronic, fast, durable), Magnetic (HDD: spinning platters, high capacity, fragile), Optical (CD/DVD: lasers, portable, slow).

What is an Embedded System?

A dedicated computer built inside a larger mechanical device to perform one specific task (e.g., washing machine, microwave).

What is the difference between a LAN and a WAN?

LAN covers a small area with local cables under single ownership. WAN covers a large geographic area using external telecoms under shared ownership.

What is a Network Protocol?

A set of agreed rules that define how devices communicate and transmit data across a network.

What is the purpose of HTTP, HTTPS, FTP, and IP?

HTTP pulls web pages. HTTPS pulls encrypted web pages. FTP transfers files. IP directs and routes packets across the internet.

What is the difference between TCP and UDP?

TCP ensures reliable delivery and resends lost packets (web/email). UDP sends packets quickly without checking arrival (gaming/streaming).

What is the difference between SMTP and IMAP?

SMTP sends emails to a server. IMAP retrieves and manages emails while keeping them synced on the server.

What are the 4 layers of the TCP/IP model from top to bottom?

1. Application Layer (HTTP, FTP, SMTP), 2. Transport Layer (TCP, UDP), 3. Internet Layer (IP), 4. Link Layer (NIC, drivers, Ethernet, Wi-Fi).

What is a Firewall?

A network security device that monitors incoming and outgoing traffic and blocks unauthorized data based on strict rules.

What is MAC Address Filtering?

A security method that allows or blocks devices from accessing a network based on their physical hardware address.

What is the difference between White Box and Black Box penetration testing?

White Box (Inside) gives the tester full knowledge and credentials. Black Box (Outside) gives zero prior knowledge to simulate an external hacker.

Identify and define the 3 social engineering tactics.

Blagging (creating a fake scenario), Phishing (mass fraudulent emails/messages), Shouldering (looking over someone's shoulder for PINs/passwords).

Identify and define the 3 types of Malware.

Virus (replicates and corrupts files), Trojan (disguised as legitimate software), Spyware (secretly records user activity/keystrokes).

What are 5 ways to detect and prevent cyber attacks?

Biometrics, strong password systems, CAPTCHAs, email confirmations, and automatic software updates.

What is the difference between a table, field, and record?

Table: Collection of data in rows/columns. Field (Column): Single attribute (e.g., Name). Record (Row): All fields for one single entity.

What is the difference between a Primary Key and a Foreign Key?

Primary Key uniquely identifies each record in a table. Foreign Key is a primary key placed in another table to link them together.

Why use a Relational Database instead of separate flat tables?

It eliminates data inconsistency (mistakes across files) and data redundancy (unnecessarily repeating the same data).

How do you format a standard SQL retrieval query?

SELECT field1, field2 FROM table_name WHERE condition ORDER BY field1 ASC;

How do you insert, update, and delete records in SQL?

INSERT INTO table (cols) VALUES (vals);

What are the 8 key technology contexts used for Paper 2 essay questions?

Cyber security, mobile technologies, wireless networking, cloud storage, hacking, wearable technologies, computer-based implants, and autonomous vehicles.

What is the core argument in the digital privacy vs security debate?

Citizens want their right to private data without surveillance, while governments argue they need access to encrypted data to stop crime and terrorism.