A1.3 Operating systems and control systems: notes and practice
A1.3 covers what an operating system does between the hardware and your programs: booting, memory, files, devices, security, scheduling and interrupts. At HL it adds multitasking and control systems with sensors, actuators and feedback.
Paper 1Mixed3 practice questions
What you need to know
Our summary of the topic in our own words, not the IB guide. Points marked HL are for Higher Level only.
- Explain what an operating system is and where it sits between hardware and applications
- Describe the boot process from secondary storage into main memory
- Describe how the operating system manages files and storage
- Describe how the operating system communicates with peripherals through device drivers
- Describe the operating system's security functions including authentication, permissions and privilege levels
- Explain how the operating system allocates and protects memory between processes
- Compare scheduling approaches such as round robin, priority and first come first served
- Choose a scheduling approach for a given workload and justify it
- Compare polling and interrupts as ways for hardware to get the processor's attention
- Describe how an interrupt is handled and why interrupt priority matters
- Explain how the operating system supports multitasking and allocates CPU time, memory and bandwidth between processesHL
- Identify the components of a control system: sensors, a processor, actuators and a feedback pathHL
- Explain the role of feedback in a closed-loop control systemHL
- Analyse a real-world control system and explain how its components interact to reach a target stateHL
Practice questions
Original questions written for the 2027 course, marked as you go. Easiest first.
- How the OS protects memory between programsWritten · Core
- Interrupts or polling for a barcode scannerWritten · Stretch
- Round robin schedulingWritten · Stretch
Exam tips for A1.3
- For scheduling questions, say why a method suits the workload in the question (for example, round robin gives every process a fair turn).
- Explain interrupts as a sequence: the signal, saving the current state, running the handler, then restoring the state.
- In control system questions, name the sensor, the processor, the actuator and the feedback loop for the system you are given.
Updated 24 October 2026. Topic codes are used as labels. Everything on this page is written by ExamSpine and is not endorsed by the IB.