GCSE Computer Science Syllabus

List the common primitive data types used in programming.

Integer, real/float, Boolean, character, and string.

What data type would you use to store the value True or False?

Boolean.

What is the difference between an integer and a real (float) data type?

An integer stores whole numbers only; a real/float stores numbers with a decimal (fractional) part.

What is casting in programming?

Converting a value from one data type to another, for example turning the string "5" into the integer $5$.

What does a subroutine, procedure, or function mean and how do a function and procedure differ?

A subroutine is a named block of reusable code; a function returns a value to the calling code, whereas a procedure carries out a task without returning a value.

What is a parameter in a subroutine?

A value passed into a subroutine so it can use that data when it runs.

State two advantages of using subroutines.

They avoid repeating code (reusability) and make programs easier to read, test, and maintain.

What is the difference between a syntax error and a logic error?

A syntax error breaks the rules of the language so the code will not run; a logic error lets the code run but produces the wrong result.

What is a runtime error?

An error that occurs while the program is executing, such as dividing by zero, causing it to crash or behave unexpectedly.

What is the purpose of test data, and name three types.

Test data checks a program works correctly. The three types are normal (valid), boundary (extreme/edge), and erroneous (invalid) data.

Convert the binary number $1011$ into denary (decimal).

$8 + 0 + 2 + 1 = 11$.

Convert the denary number $25$ into 8-bit binary.

$00011001$.

How many different values can be represented using $n$ bits?

$2^{n}$ different values.

What is a byte, and how many bits does it contain?

A byte is a unit of storage made up of $8$ bits.

Convert the binary number $11111010$ into hexadecimal.

$FA$ (since $1111 = F$ and $1010 = A$).

Convert the hexadecimal value $2D$ into denary.

$2 \times 16 + 13 = 45$.

Why is hexadecimal used instead of binary by programmers?

It is more compact and easier for humans to read and write; one hex digit represents exactly four binary bits, so conversion is simple and errors are reduced.

How is a single character stored in a computer?

As a binary code using a character set such as ASCII or Unicode, where each character maps to a unique number.

How is an image stored as binary data?

As a grid of pixels, where each pixel's colour is represented by a binary code; more bits per pixel (colour depth) allow more colours.

Give the formula for the file size of an image in bits.

$\text{file size} = \text{width} \times \text{height} \times \text{colour depth (bits per pixel)}$.

How is sound stored digitally?

By sampling the analogue wave at regular intervals; each sample's amplitude is stored as a binary number, with sample rate and bit depth affecting quality and size.

What is the difference between lossy and lossless compression?

Lossy compression permanently removes some data to reduce size (quality can drop); lossless compression reduces size with no loss of data so the original can be perfectly restored.

What is the purpose of compression?

To reduce file size so files take up less storage space and transfer faster over networks.

What is the difference between hardware and software?

Hardware is the physical components of a computer; software is the programs and instructions that run on the hardware.

What is the difference between system software and application software?

System software (e.g. the operating system) manages and runs the computer; application software lets the user perform specific tasks such as writing documents.

State three functions of an operating system.

Managing memory, managing the processor and running processes, and managing input/output devices/peripherals (also file and user management).

What is the difference between RAM and ROM?

RAM is volatile read/write memory holding currently running programs and data; ROM is non-volatile read-only memory holding start-up instructions such as the boot program.

What is virtual memory?

Space on secondary storage used as extra RAM when main memory is full, allowing more programs to run at the cost of slower performance.

Name the three main types of secondary storage and give one example of each.

Magnetic (hard disk drive), optical (CD/DVD/Blu-ray), and solid state (SSD/USB flash drive).

Describe the fetch-decode-execute cycle carried out by the CPU.

The CPU fetches the next instruction from memory, decodes it to work out what is required, then executes (carries out) it; this repeats continuously.

Name three factors that affect CPU performance.

Clock speed, number of cores, and cache size.

What is the role of cache memory?

It is small, very fast memory close to the CPU that stores frequently used data and instructions to speed up processing.

Describe the star network topology.

All devices connect to a central switch or hub; if one cable fails only that device is affected, but failure of the central device disables the whole network.

Describe the mesh network topology.

Devices are interconnected with multiple paths between them, so data can be rerouted if one link fails, making it very reliable but expensive to cable.

Compare a LAN and a WAN.

A LAN (Local Area Network) covers a small geographic area such as one building and is usually owned by one organisation; a WAN (Wide Area Network) covers a large geographic area, such as the internet, often using third-party infrastructure.

What is the difference between wired and wireless network connections?

Wired connections (e.g. Ethernet cables) are typically faster and more secure and reliable; wireless (e.g. Wi-Fi) offers mobility and easier setup but can be slower and less secure.