All 14 Computer Science topics for Cambridge IGCSE, grouped the way the exam is. Each topic has a few flashcards to test yourself; the full sets are free in Socrates AI.
Why do computers use binary?
Their circuits have two states (on and off), represented by 1 and 0.
What is a bit, a nibble and a byte?
Bit: one binary digit. Nibble: 4 bits. Byte: 8 bits.
Convert the binary number 1011 0110 to denary.
128 + 32 + 16 + 4 + 2 = 182.
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What is a character set?
A defined list of characters recognised by a computer, each with a unique binary code.
Compare ASCII and Unicode.
ASCII uses 7 bits (128 characters, extended ASCII 8 bits); Unicode uses more bits (up to 32) to represent characters from all languages and emoji.
Why do the ASCII codes of 'A' and 'B' differ by 1?
Characters are coded in sequence, so consecutive letters have consecutive codes (A = 65, B = 66).
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Why is data compressed?
To reduce file size, so files take less storage and transfer faster over networks.
What is lossy compression?
Compression that permanently removes some data, e.g. detail that humans are unlikely to notice.
What is lossless compression?
Compression that reduces file size without losing any data; the original can be restored exactly.
What is a network?
Two or more computers connected together to share data and resources.
What is the difference between a LAN and a WAN?
A LAN covers a small area, such as a building, with its own hardware; a WAN covers a large area, often using leased or third-party connections.
Give two advantages of networking computers.
Sharing files, printers and internet access; central backups and security; communication.
What is the internet?
A worldwide network of networks.
What is the World Wide Web?
A collection of web pages and resources accessed over the internet using browsers.
What is a protocol?
A set of rules that allow devices to communicate.
What does the CPU do?
It processes data and instructions by carrying out the fetch–decode–execute cycle.
What does the ALU do?
Carries out arithmetic calculations and logical operations.
What does the control unit do?
Decodes instructions and sends control signals to coordinate the other parts of the computer.
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What is primary memory?
Memory the CPU can access directly: RAM, ROM and cache.
What is RAM used for?
Storing the data and programs currently in use; it is volatile.
What is ROM used for?
Storing the start-up instructions (bootstrap/BIOS); it is non-volatile and read-only.
What is the difference between system software and application software?
System software runs the computer (operating system, utilities); application software does user tasks (word processors, games).
Give four functions of an operating system.
Managing memory, managing the processor (multitasking), managing files, managing peripherals via drivers, managing users and security, and providing a user interface.
What is a device driver?
Software that lets the operating system communicate with a hardware device.
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What is malware?
Malicious software designed to damage, disrupt or gain unauthorised access to a computer.
What is a virus?
Malware that attaches to files and spreads when the file is run.
What is a worm?
Malware that replicates and spreads across networks by itself.
What does "ethical" mean in computing?
Whether an action is morally right or wrong.
Give two privacy concerns about technology.
Personal data collected and shared without consent, location tracking, and surveillance cameras with facial recognition.
What is the digital divide?
The gap between people who have access to technology and the internet and those who do not.
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What is an algorithm?
A sequence of steps that solves a problem or completes a task.
What is decomposition?
Breaking a problem down into smaller, more manageable sub-problems.
What is abstraction?
Removing unnecessary detail to focus on what matters for solving the problem.
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What is a variable?
A named memory location whose value can change while the program runs.
What is a constant?
A named value that does not change while the program runs.
Name five data types.
Integer, real (float), Boolean, character and string.
What is a database?
An organised, persistent collection of data.
What are a table, record and field?
Table: data about one type of thing. Record: one row, about one item. Field: one column, one piece of data.
What is a primary key?
A field that uniquely identifies each record in a table.
What does an AND gate output?
1 only if both inputs are 1.
What does an OR gate output?
1 if either or both inputs are 1.
What does a NOT gate do?
It inverts the input: 1 becomes 0 and 0 becomes 1.
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