Memory Management · Process Scheduling · File Management · Interrupts · User Interface
CSZoneCambridge IGCSE Computer Science 0478
Core OS Functions
What the OS Does
Memory management: allocates RAM to programs; manages virtual memory; decides what stays in RAM and what gets swapped
Process management / scheduling: decides which programs run and for how long; handles multitasking (switching rapidly between processes)
File management: organises files and folders on storage; controls read/write access; manages permissions
Device management: communicates with hardware via device drivers; manages input/output operations
Interrupts
How Hardware Gets CPU Attention
An interrupt is a signal sent to the CPU to indicate that an event requires attention. The CPU pauses its current task, saves its state, and runs an interrupt service routine (ISR) to handle the event, then resumes.
Higher priority interrupts pre-empt lower ones — critical events (e.g. power failure) handled first
Without interrupts, the CPU would have to continuously poll (check) every device for changes
User Interface Types
How Users Interact with the OS
GUI (Graphical User Interface): windows, icons, menus, pointer. Intuitive, no commands needed. Examples: Windows, macOS, Android.
CLI (Command Line Interface): text commands typed by user. Faster for experts, uses less memory, can be scripted for automation. Examples: Linux terminal, Windows PowerShell.
Voice/gesture interface: used in smartphones, smart speakers (Siri, Alexa), virtual reality headsets.
Exam Practice
Have a go at this question
Cambridge IGCSE 0478 style
Describe what happens in the CPU when an interrupt signal is received from a keyboard.
4 marks
The CPU finishes the current instruction [1] and saves its current state (registers/program counter) [1]. The CPU runs the appropriate interrupt service routine (ISR) to process the keyboard input [1]. When the ISR is complete, the CPU restores its previous state and continues where it left off [1].
Key Takeaways
What to Remember
OS functions: memory, process, file, device management + user interface
Interrupt: signal to CPU → save state → run ISR → restore state and continue
GUI: icons and windows, intuitive; CLI: text commands, powerful for experts
Process scheduling: OS shares CPU time between multiple programs (multitasking)