IGCSE Computer Science: Hardware (Cambridge 0478)

Topic 3 of Cambridge IGCSE Computer Science (0478) is Hardware – the physical components that make computing possible. It sits in the “Computer systems” half of the syllabus (Topics 1-6), examined on Paper 1, and is one of the largest topics in the course with four sub-topics: computer architecture, input and output devices, data storage, and network hardware.

3.1 Computer architecture

This sub-topic covers what happens inside the CPU. You need to understand the role of the central processing unit – processing instructions and data that are input into the computer so a result can be output – and what is meant by a microprocessor (a type of integrated circuit on a single chip).

For a computer with Von Neumann architecture, you must know the purpose of each internal component and be able to describe the fetch-decode-execute (FDE) cycle:

• Units: the arithmetic logic unit (ALU) and the control unit (CU)
• Registers: the program counter (PC), memory address register (MAR), memory data register (MDR), current instruction register (CIR) and accumulator (ACC)
• Buses: the address bus, data bus and control bus, which transmit data, addresses and signals between components

The FDE cycle itself describes how instructions and data are fetched from RAM into the CPU, processed by these components, and then executed – data and addresses are stored into specific registers, and buses carry information between them.

Beyond the cycle itself, you need to understand what is meant by a core, cache and clock in a CPU, and how each affects performance (more cores, a larger cache and a faster clock speed can all improve performance), the purpose of an instruction set (the list of commands a CPU can process, given in machine code), and the purpose and characteristics of an embedded system – a system built to perform one dedicated function (for example in domestic appliances, cars, security systems, lighting systems or vending machines), as distinct from a general-purpose computer such as a PC or laptop that runs many different functions.

3.2 Input and output devices

This sub-topic is largely a named list you need to recognise and be able to select appropriately for a given scenario, plus an understanding of sensors as a distinct category.

Input devices named in the syllabus include: barcode scanner, digital camera, keyboard, microphone, optical mouse, QR code scanner, touch screen (resistive, capacitive and infra-red), and 2D and 3D scanners.

Output devices named in the syllabus include: actuator, digital light processing (DLP) projector, inkjet printer, laser printer, LED screen, LCD projector, LCD screen, speaker and 3D printer.

Sensors are treated separately: you need to understand what a sensor is and its purpose, then identify what type of data each named sensor captures and when it would be used. The named sensors are: acoustic, accelerometer, flow, gas, humidity, infra-red, level, light, magnetic field, moisture, pH, pressure, proximity and temperature. Exam questions commonly present a real-world scenario (a greenhouse, a security system, a car) and ask you to select and justify the most suitable sensor – this requires knowing what each sensor actually measures, not just its name.

3.3 Data storage

This sub-topic separates storage into primary, secondary and cloud categories.

Primary storage is directly accessed by the CPU and includes random access memory (RAM) and read only memory (ROM). You need to understand why a computer needs both, and the difference between them (RAM is volatile and holds data/instructions currently in use; ROM is non-volatile and typically holds the startup instructions).

Secondary storage is not directly accessed by the CPU and is used for more permanent data storage. Three technologies are named:

• Magnetic storage – uses platters divided into tracks and sectors, with data read and written using electromagnets (hard disk drive, HDD)
• Optical storage – uses lasers to create and read pits and lands (CD, DVD, Blu-ray)
• Solid-state (flash memory) – uses NAND or NOR technology with transistors as control gates and floating gates (SSD, SD card, USB drive)

You also need to describe virtual memory – how pages of data are transferred between RAM and virtual memory when needed, and why this is necessary – and cloud storage, including its advantages and disadvantages compared with storing data locally (remote accessibility versus the need for physical servers and storage to host it).

3.4 Network hardware

The final sub-topic covers the hardware and addressing that make networking possible:

• A computer needs a network interface card (NIC) to access a network.
• Every NIC is given a MAC address at the point of manufacture, usually written in hexadecimal and built from a manufacturer code and a serial code.
• An IP address is allocated by the network and can be static or dynamic; you need to know the characteristics of, and differences between, IPv4 and IPv6.
• A router sends data to a specific destination on a network, can assign IP addresses, and connects a local network to the internet.

This sub-topic connects directly to Topic 2 (Data transmission) – understanding how a router directs packets to their destination builds on the packet-switching content covered there, so revising the two topics together reinforces both.

How to approach it

Computer architecture (3.1) is the conceptually hardest part of this topic and the one most worth drilling with practice diagrams: being able to trace a single instruction through fetch, decode and execute, naming which register or bus is involved at each step, is a skill that only comes from repetition. For 3.2, build yourself a quick-reference table of sensor names against what they actually measure, since scenario-based questions reward precise matching over general familiarity. For 3.3 and 3.4, focus on the comparisons the syllabus explicitly asks for – RAM vs ROM, primary vs secondary storage, local vs cloud storage, IPv4 vs IPv6 – since “explain the difference between” questions are a recurring format across this topic.

Official syllabus

Cambridge International, Cambridge IGCSE Computer Science (0478) syllabus for examination in 2026, 2027 and 2028 (Version 5, published December 2025): official syllabus PDF, Subject content, section 3 “Hardware”. Verified 2026-09-02.