Recognise hardware and software interrupts
Classify common interrupt causes and explain how they request the processor's attention.
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
What can an interrupt tell a computer?
What you will learn
- Explain what an interrupt signals
- Identify keyboard and mouse as hardware interrupt examples
- Identify division by zero and memory conflicts as software interrupt examples
An interrupt signals an event needing attention
An interrupt is a signal that causes the processor or operating system to pause its normal sequence and respond to an event. A hardware interrupt can be generated by an external device, such as a key being pressed or a mouse being moved.
Apply and check the rule
A software interrupt can be raised by a program condition, such as division by zero or two processes trying to access the same memory location. The operating system can handle the event so the system responds appropriately rather than silently ignoring it.
Pause and explain
Which is a hardware interrupt example in the syllabus?
Worked example
A user presses a key while a program is running. What event occurs?
Show the worked solution
- The keyboard reports an input event.
- It generates a hardware interrupt.
- The operating system can handle the event and pass the input to the right program.
Answer A keyboard hardware interrupt requests attention so the key input can be handled.
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.
Classify a keyboard key press as hardware or software interrupt.
Give me a hint
Identify whether the event originates from a physical device.
Compare my reasoning
- A keyboard is a hardware device.
- The key press creates a hardware interrupt.
Hardware interrupt
Look for these in your work
- Device identified
- Interrupt type correct
A running program attempts to divide by zero. Classify the interrupt and name the cause.
Give me a hint
The condition comes from program execution.
Compare my reasoning
- The event originates in software execution.
- Division by zero is the triggering condition.
Software interrupt caused by division by zero.
Look for these in your work
- Software origin
- Cause named
Two processes attempt to access the same memory location. Explain why the operating system may need to respond through an interrupt.
Give me a hint
Consider coordination and data integrity.
Compare my reasoning
- The simultaneous access can create a conflict.
- An interrupt signals that the event needs attention.
- The OS can coordinate access to prevent an unsafe or inconsistent result.
The conflict needs system attention; an interrupt can invoke OS handling so access is coordinated rather than allowed to produce an inconsistent state.
Look for these in your work
- Conflict identified
- Interrupt purpose
- OS response
Common mistakes
- Calling division by zero a hardware interrupt
- Assuming an interrupt is always an error
What can you explain now?
A program attempts division by zero. What type of interrupt example is this?
Compare with the explanation
Software interrupt
The cause is a condition in program execution rather than an external device.
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Make it stick
Give one hardware interrupt example and one software interrupt example.
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.