Trace the hardware–firmware–operating system stack
Explain the dependency chain that allows an application to start on a computer.
This sequence follows Cambridge IGCSE Computer Science 0478, 2026–2028 syllabus Version 6. It covers subject content sections 4.1–4.2 only. The separately published 2029–2031 syllabus is not mapped here. Practice is original, self-checked and does not award an official Cambridge grade. Full timed papers and human subject-teacher review remain outstanding.
Before you begin
- No programming language is required. Be comfortable with place value and multiplication; each lesson introduces the computer-science notation it uses.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which software provides the platform for applications?
What you will learn
- Define the roles of hardware, firmware, operating system and application software
- Place the bootloader in the start-up sequence
- Explain why each layer depends on the one below
Start-up proceeds through layers
The hardware powers the computer. Firmware, including its bootloader, runs on the hardware and starts the operating system. The operating system then provides the platform on which application software runs.
Apply and check the rule
The layers have different responsibilities: hardware performs physical operations, firmware provides low-level start-up control, the operating system manages general computer resources and applications provide user tasks. An application cannot normally run before the OS is available.
Pause and explain
What must happen before an application can run in the syllabus model?
Worked example
Put these in the order needed to launch a word processor: hardware, operating system, application, firmware.
Show the worked solution
- The hardware powers and executes instructions.
- Firmware runs the bootloader and starts the operating system.
- The operating system loads the word processor.
Answer Hardware → firmware/bootloader → operating system → application
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Complete the start-up chain: hardware → ____ → operating system → browser.
Give me a hint
The bootloader is part of this layer.
Compare my reasoning
- Firmware runs on the hardware.
- It starts the operating system.
- The operating system launches the browser.
Firmware
Look for these in your work
- Firmware inserted
- OS sequence explained
Explain one reason a browser depends on the operating system.
Give me a hint
Consider services the OS provides.
Compare my reasoning
- The OS provides a platform for applications.
- It manages memory, files and peripherals used by the browser.
- The browser relies on those shared resources.
The browser is application software that uses the OS platform and shared resources to run.
Look for these in your work
- OS platform
- Resource examples
- Dependency explained
A computer has working hardware and an operating system file on its drive, but its firmware cannot start. Why might the user still be unable to open an application?
Give me a hint
Follow the layers from hardware upward.
Compare my reasoning
- The bootloader in firmware starts the operating system.
- Without the firmware start-up step, the OS may not load.
- Without the OS platform, the application cannot run normally.
The bootloader/firmware is needed to start the OS; the application depends on the OS. Failure at the lower start-up layer blocks the higher layers.
Look for these in your work
- Firmware role
- OS dependency
- Application consequence
Common mistakes
- Putting the operating system before firmware in the start-up chain
- Treating firmware as a user application
What can you explain now?
What does the bootloader do in the start-up sequence?
Compare with the explanation
Firmware on the hardware starts the operating system
The bootloader is part of firmware and begins the OS start-up process.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Name the four layers in start-up order, from hardware to user application.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.