2.1 · Operating Systems
Goal: describe the major functions of an OS and compare common ones.
What an OS does — six core jobs
| Function | What it does | Example |
|---|---|---|
| Process management | Schedule and switch between programs | Run Chrome + Word + music player simultaneously |
| Memory management | Allocate RAM, swap to disk if needed | Open more tabs than your RAM holds; OS pages out the oldest |
| File management | Maintain folders, permissions, free space | Save file to D:\projects\ |
| Device management | Talk to hardware via drivers | Print job sent to the printer driver |
| User & security management | Logins, passwords, permissions | Standard vs Administrator account |
| User interface (UI) | GUI or CLI | Windows desktop vs Linux terminal |
Without these, your hardware would be a useless box.
Common operating systems
| OS | Typical user | Notes |
|---|---|---|
| Microsoft Windows | Desktops, offices, gamers | Closed source, ~75% PC market |
| macOS | Apple Mac users | Unix-based |
| Linux distros (Ubuntu, Debian, Fedora) | Developers, servers, supercomputers | Open source, free |
| Android | Smartphones, tablets | Linux kernel + Google's stack |
| iOS / iPadOS | iPhones, iPads | Closed, tightly integrated with hardware |
| Chrome OS | Light laptops, education | Browser-centric, fast updates |
| Embedded OS (e.g. FreeRTOS, VxWorks) | IoT devices, cars, satellites | Tiny footprint, deterministic |
Multi-tasking vs Multi-user vs Multi-processing
| Term | Meaning |
|---|---|
| Multi-tasking | One CPU, multiple programs sharing time (rapid switching) |
| Multi-user | One machine, multiple users logged in (timesharing or remote) |
| Multi-processing | Multiple CPUs / cores doing real parallel work |
Modern OSes support all three.
GUI vs CLI
| Feature | GUI | CLI |
|---|---|---|
| Beginners | Easy | Steep learning curve |
| Power users | Slower for repetitive tasks | Fastest with scripts |
| Resource use | Heavier | Tiny |
| Automation | Limited | Excellent (shell scripts) |
Most modern OSes offer both.
Exam-style question
Q (4 marks): Outline four functions of an operating system, and explain why an OS is essential for running multiple applications at once.
Sample answer:
- Process management — schedules CPU time so several applications run concurrently.
- Memory management — allocates and protects RAM between processes.
- File management — provides directories, permissions, and a unified file API.
- Device management — communicates with peripherals via drivers.
Without an OS, each application would have to talk directly to the hardware and manage its own memory; two apps wanting the same resource (e.g. the speaker) would clash. The OS arbitrates so the user can run Chrome, Word and a music player simultaneously without manual coordination.
Key takeaways
- OS = process + memory + file + device + security + UI.
- Many flavours: Windows, macOS, Linux, Android, iOS, Chrome OS, embedded.
- Multi-tasking, multi-user, multi-processing all coexist today.
➡️ Next: 2.2 Utilities & Drivers