Introduction
An Operating System (OS) is the most important system software — it acts as an intermediary between the
user and the computer hardware, managing all resources and providing the interface through which every
other program runs.
Key Functions of an Operating System
| Function | Description |
|---|
| Process Management | Manages execution of multiple programs, allocating CPU time to each |
| Memory Management | Allocates and deallocates memory (RAM) to running programs |
| File Management | Organises data into files/folders, manages storage devices |
| Device Management | Controls peripheral devices via drivers |
| Security | User authentication, access control, protection from unauthorised access |
| User Interface | Provides GUI (Graphical User Interface) or CLI (Command Line Interface) for interaction |
Types of Operating Systems
| Type | Description | Example |
|---|
| Batch OS | Processes jobs in batches without user interaction during execution | Early mainframe systems |
| Time-Sharing OS | Allows multiple users to share system resources simultaneously via time slices | UNIX |
| Real-Time OS (RTOS) | Processes data within a strict, guaranteed time constraint | Used in medical devices, aircraft systems |
| Distributed OS | Manages a group of independent computers as a single system | Used in cloud computing environments |
| Multi-user OS | Allows multiple users to access the system concurrently | Linux, UNIX |
| Mobile OS | Designed for smartphones/tablets | Android, iOS |
GUI vs CLI
| Interface | Description | Example |
|---|
| GUI (Graphical User Interface) | Visual, icon/window-based interaction using a mouse | Windows, macOS |
| CLI (Command Line Interface) | Text-based commands typed by the user | MS-DOS, Linux Terminal |
Popular Operating Systems
| OS | Developer | Type |
|---|
| Windows | Microsoft | Proprietary, GUI-based |
| macOS | Apple | Proprietary, GUI-based (for Mac computers) |
| Linux | Open-source community (based on Linus Torvalds' kernel) | Open-source, multiple distributions (Ubuntu, Fedora) |
| Android | Google | Open-source, mobile-focused |
| iOS | Apple | Proprietary, mobile-focused |
Booting Process
Flowchart — Computer Booting Sequence
Power ON
↓
POST (Power-On Self-Test) — BIOS/UEFI checks hardware components
↓
Bootloader locates and loads the Operating System from storage into RAM
↓
OS takes control, loads user interface — computer ready for use
📌 Cold Boot vs Warm Boot: A "cold boot" starts the computer from a completely powered-off state (full POST); a "warm boot" restarts the OS without powering off completely (e.g., Windows restart) — usually faster since some hardware checks are skipped.
✅ UPSC/SSC Focus: Six key OS functions · Types of OS (batch, time-sharing, real-time, distributed) · GUI vs CLI distinction · Popular OS-developer matching · Booting sequence (POST → bootloader → OS load).