What is an operating system?
An operating system is system software that manages the computer's hardware and software and acts as a bridge between the user and the hardware. It is the first program loaded when the computer starts (booting). Examples: Windows, Linux (Ubuntu), macOS, Android, iOS.
Functions of an operating system
- Process management: a running program is a process. The OS decides which process gets the CPU and for how long, switching very fast so many seem to run at once (multitasking).
- Memory management: gives RAM to each program, keeps programs from using each other's memory, and frees memory when a program ends.
- File management: creates, opens, saves, copies, renames and deletes files and folders; keeps track of where each file is stored.
- Device management: controls input/output devices using device drivers and handles requests from programs to use them.
- Security: user accounts, passwords, permissions, protection from unauthorised access.
User interface
The user interface (UI) is the way the user and the OS talk to each other.
- Command-line interface (CLI): you type commands (e.g.
dir,ls,cd). Fast for experts, uses little memory, but you must remember commands. Example: MS-DOS, Linux terminal. - Graphical user interface (GUI): windows, icons, menus and a pointer (WIMP). Easy to learn. Example: Windows, macOS.
- Touch-based: tap, swipe and pinch on a touch screen. Example: Android, iOS.
- Voice-based: you speak commands. Example: phone assistants.
- Gesture-based: hand or body movements in front of a sensor or camera.
Board exam focus
Expect: list and explain any three functions of an OS (3 marks), difference between CLI and GUI, name the interface used by a smartphone.
Key formulas and definitions
- OS functions: Process, Memory, File, Device, Security
- Process = a program that is running
- CLI = type commands; GUI = windows, icons, menus, pointer
- Other UIs: touch, voice, gesture
Worked examples
1. You play music, download a file and type a document at the same time. Which OS function makes this possible?
Process management. The OS gives each process short turns on the CPU so they all move forward together (multitasking). Memory management also gives each its own RAM.
2. Give two differences between CLI and GUI.
CLI: commands are typed, harder for beginners, uses less memory. GUI: icons and menus are clicked, easy to learn, needs more memory and graphics.
3. A game crashes but the browser still works. Which OS function protected the browser?
Memory management: each program has its own memory area, so one program's crash does not spoil another's memory.
4. Which UI is used by a smart speaker? By a phone?
Smart speaker: voice-based UI. Phone: mainly touch-based, with voice as an extra.
Common mistakes
- Calling the OS an application. It is system software.
- Thinking programs truly run at the same instant on one CPU core. The OS switches between them very fast.
- Mixing up GUI and touch UI. Touch is a separate way of input, though phones also show a graphical screen.
- Forgetting security as an OS function.