Operating systems, processes and interrupts
Explain how an operating system manages accounts, files, memory, processes, devices and interrupts.
Section Component 1 · Computer Systems and Logic
Mapped to the Cambridge IGCSE Computer Science 0265 syllabus for exams in 2029. These original explanations and self-checks are independent study support, not Cambridge papers, official marks or grades. Practical programming is taught with worked code and trace tasks; an executable Python workspace and timed digital-exam simulation are not yet available.
Before you begin
- Use the 2029 syllabus for this course. Cambridge specifies Python 3.10 or higher for programming and digital exams for both components. The syllabus currently identifies this route for 2029 only; confirm later-year availability with Cambridge and your school.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Before operating systems, processes and interrupts, which statement is the safest starting point?
What you will learn
- Describe the operating system as a resource manager and interface
- Explain file, memory, process and peripheral management
- Trace an interrupt and return to the interrupted process
The operating system manages shared resources
An operating system provides an interface for users and applications and manages hardware resources. It manages accounts and permissions, tracks files through a file system, and groups them in directories so users and programs can organise and locate them.
Memory management allocates RAM to processes, loads them, protects one process from another and can use paging or segmentation to organise memory. Paging uses fixed-size blocks; segmentation divides a process into logical parts such as code and data. When RAM is insufficient, virtual memory stores inactive pages on backing storage.
Processes and interrupts need coordination
Process management schedules which process uses the CPU and supports inter-process communication so processes can exchange data or signals. Peripheral management relies on device drivers that translate operating-system requests into commands a device understands.
A hardware interrupt can signal an event such as a key press or device completion; a software interrupt can be caused by a program request or exception. The operating system saves enough state, runs an interrupt service routine (ISR), handles the event and restores the interrupted process so it can resume.
Pause and explain
Which habit best checks your understanding of operating systems, processes and interrupts?
Worked example
A key press occurs while a program is running. Explain how an interrupt lets the computer handle it.
Show the worked solution
- The keyboard signals a hardware interrupt.
- The OS pauses the current process and runs the keyboard ISR.
- After handling the key, the OS restores the saved state so the process can resume.
Answer The OS handles the interrupt with an ISR, then returns to the interrupted process.
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.
An OS prevents one application from reading another application's protected memory. Name the management function and explain its purpose.
Give me a hint
Identify the memory-management protection boundary.
Compare my reasoning
- The OS assigns and tracks memory for processes.
- Memory protection blocks a process from accessing another process's protected region.
- This reduces interference and limits damage from faults or malicious behaviour.
Memory protection within memory management.
Look for these in your work
- Function named
- Access rule explained
- Purpose stated
A printer receives a print request from an application. Explain the roles of the OS and device driver.
Give me a hint
Trace the request from software to hardware.
Compare my reasoning
- The application asks the OS to print.
- The OS coordinates the request and uses a printer driver.
- The driver translates the request into commands the printer can process.
The OS coordinates; the driver translates the request for the printer hardware.
Look for these in your work
- Request path
- OS role
- Driver role
A timer interrupt occurs during a long calculation. Explain how the OS can use it to share CPU time fairly.
Give me a hint
Connect the interrupt, scheduling and saved process state.
Compare my reasoning
- The timer signals that a time slice has ended.
- The OS runs the timer ISR and saves the current process state.
- The scheduler can select another process; the original can resume later from its saved state.
The timer interrupt lets the scheduler pause one process and run another, preserving state for later resumption.
Look for these in your work
- Timer purpose
- Scheduler decision
- Resume state
Common mistakes
- Saying an interrupt permanently terminates the current process.
- Confusing a device driver with the physical device.
- Describing virtual memory as a substitute with RAM's speed.
What can you explain now?
What is the routine called that handles an interrupt?
Compare with the explanation
Interrupt service routine (ISR)
The operating system uses an ISR to respond to the event.
After trying it yourself, choose your next review. This is your self-assessment.
Your review choice appears on Today. Sign in to sync it across devices.
Make it stick
How does an operating system coordinate memory, processes, devices and interrupts?
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.