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1. Introduction

An operating system (OS) is the most important system software that manages and controls the entire computer. It acts as an interface between the user and the computer hardware. When we switch on a computer, the operating system is the first program that loads into the memory, and it keeps running until the computer is switched off. Without an operating system, a computer is just a collection of hardware parts that cannot do any useful work, because the user cannot communicate with the hardware directly.

The operating system performs many tasks. It starts the computer, manages the CPU, memory, storage and input-output devices, organises files and folders, and runs application programs. It also provides a friendly way for the user to give commands to the computer. Popular operating systems include Microsoft Windows, Linux, macOS, Android and iOS. This chapter explains what an operating system is, its functions, the types of operating systems, the process of starting a computer called booting, and the basics of files, folders and windows.

2. Functions of an Operating System

The operating system performs several important functions to make the computer useful and easy to use.

Managing memory: The OS keeps track of the primary memory (RAM) and decides which programs use which part of it. It ensures that every running program gets enough memory and that programs do not interfere with each other.

Managing the processor: The CPU can handle only one instruction at a time. The OS schedules the tasks so that the CPU is shared among all the running programs in a fair and efficient way.

Managing input and output devices: The OS receives data from input devices like the keyboard and mouse, and sends results to output devices like the monitor and printer. It uses device drivers to communicate with each device.

Managing files and folders: The OS organises data into files and folders, lets the user create, rename, copy, move and delete them, and stores them on the disk in an organised way.

Providing the user interface: The OS provides a way for the user to interact with the computer. This can be a command-line interface (CLI), where the user types commands, or a graphical user interface (GUI), where the user clicks on icons and windows.

Running application software: The OS provides a platform on which application software like Word, Excel and browsers can run.

3. Types of Operating Systems

Operating systems can be classified in different ways. Based on the interface, they are of two types: Command Line Interface (CLI), where the user types text commands, for example MS-DOS, and Graphical User Interface (GUI), where the user works with icons, menus and windows, for example Windows and Linux.

Based on the number of users, operating systems can be single-user or multi-user. A single-user OS is used by one person at a time, while a multi-user OS allows many users to use the computer at the same time. Based on the number of tasks, they can be single-tasking, which runs one program at a time, or multitasking, which runs several programs at the same time. Modern operating systems like Windows are single-user, multitasking GUI systems.

Microsoft Windows is the most widely used operating system for personal computers. It was developed by Microsoft and has gone through many versions such as Windows 98, Windows XP, Windows 7, Windows 10 and Windows 11. It provides a GUI with a Start button, taskbar, desktop, icons and windows.

Linux is a free and open-source operating system. Anyone can download, use and modify its code. It is considered very secure and stable, and is widely used on servers. Ubuntu, Fedora and Red Hat are popular versions of Linux.

macOS is the operating system developed by Apple for its Macintosh computers. It is known for its simple, elegant design. Android and iOS are operating systems for mobile phones and tablets.

5. Booting

The process of loading the operating system into the main memory when the computer is switched on is called booting. When we press the power button, the CPU looks for the boot instructions. These instructions are stored in the ROM. The computer then loads the operating system from the hard disk into the RAM. The process ends when the desktop screen appears and the computer is ready for use.

There are two types of booting: cold booting, when the computer is switched on after being completely off, and warm booting, when the computer is restarted using the restart option without switching off the power.

6. Files, Folders and Windows

File: A file is a collection of related data stored under a single name, such as a letter, a picture or a song. Every file has a name and an extension that tells its type, for example document.docx, image.jpg and music.mp3.

Folder: A folder (also called a directory) is a container that stores files and other folders. Folders help organise files so they can be found easily. A folder can be created, renamed, copied, moved and deleted.

Window: A window is a rectangular area on the screen that displays a program or a folder. Every window has a title bar, a minimise button, a maximise button and a close button. Working with the mouse, icons and windows on the desktop is the essence of a graphical user interface.

Quick Revision Tables

Table 1: Functions of an Operating System

Function What it does
Memory management Allocates RAM to running programs
Processor management Schedules tasks for the CPU
Device management Handles input and output devices
File management Creates and organises files and folders
User interface Gives a CLI or GUI to the user
Platform for software Runs application programs

Table 2: Types of Operating Systems

Basis of classification Types Examples
Interface CLI and GUI MS-DOS (CLI), Windows (GUI)
Number of users Single-user, multi-user Windows (single), Unix (multi)
Number of tasks Single-tasking, multitasking MS-DOS (single), Windows (multi)

Mind Map

flowchart TD A["Operating System"] --> B["Functions"] A --> C["Types"] A --> D["Popular OS"] A --> E["Booting"] A --> F["Files and Folders"] B --> B1["Memory Management"] B --> B2["Processor Management"] B --> B3["Device Management"] B --> B4["File Management"] B --> B5["User Interface"] C --> C1["CLI vs GUI"] C --> C2["Single-user vs Multi-user"] C --> C3["Single-tasking vs Multitasking"] D --> D1["Windows"] D --> D2["Linux"] D --> D3["macOS"] D --> D4["Android"] E --> E1["Cold Booting"] E --> E2["Warm Booting"]

Important Diagrams (SVG)

Diagram 1: The OS as an Interface

USER OPERATING SYSTEM Interface between user and hardware CPU MEMORY (RAM) STORAGE (Disk) INPUT / OUTPUT PERIPHERALS Hardware Hardware Hardware Golden Rule: The operating system sits between the user and the hardware and manages all resources. It manages the CPU, memory, storage and every input-output device.

Diagram 2: The Boot Process

POWER ON Press the power button BOOT INSTRUCTIONS Read from ROM OS LOADED From disk into RAM DESKTOP Computer ready for use Types of Booting COLD BOOTING Starting after power was off WARM BOOTING Restart without power off Full boot sequence from start Uses the restart option Golden Rule: Booting is the process of loading the operating system into RAM when the computer starts. Cold boot is from off state; warm boot is a restart.

Common Mistakes

  1. Saying the operating system is application software. It is system software, the most important one.
  2. Writing that boot instructions are stored in RAM. They are stored in ROM; the OS is loaded into RAM during booting.
  3. Confusing CLI with GUI. In CLI the user types commands (MS-DOS); in GUI the user clicks icons and windows.
  4. Believing a folder is a file. A folder is a container that stores files and other folders.
  5. Saying Windows is the only operating system. There are also Linux, macOS, Android and iOS.
  6. Forgetting that a multi-user OS allows many users at the same time, while a single-user OS allows one.
  7. Writing that warm booting switches off the power. Warm booting restarts the computer without switching off power.
  8. Calling the desktop an application. The desktop is the main screen of the GUI shown after booting.
  9. Thinking the OS stores data directly. The OS manages files and folders but does not create the content of files itself.

Exam Tips

  1. Memorise all six functions of an operating system: memory, processor, device, file management, user interface and platform.
  2. Remember that the OS is an interface between the user and the hardware, and draw the diagram in exams.
  3. Know the difference between cold booting and warm booting with a one-line definition of each.
  4. Give at least three examples of operating systems, one of each type: Windows, Linux and macOS.
  5. Learn the file extension examples: .docx, .jpg, .mp3 and mention that a folder can hold both files and sub-folders.
  6. Distinguish clearly between single-user and multi-user, and single-tasking and multitasking.
  7. Remember Linux is open source and free, and Android and iOS are mobile operating systems.

Conclusion

The operating system is the heart of a computer system. It manages memory, the processor, devices, files and the user interface, and provides the platform on which all application software runs. Operating systems can be classified on the basis of their interface, the number of users and the number of tasks they handle, with Windows, Linux and macOS being the most popular. The process of loading the OS at startup is called booting, and after booting, the user works with files, folders and windows on the desktop. With the operating system understood, the next chapters focus on application software such as word processors, spreadsheets and presentation tools.