An operating system, often written as OS, is the most important program that runs on a computer. It is the first software to start when the computer is switched on and the last software to close when the computer is shut down. The operating system manages all the hardware, runs all the other programs, and provides the user with a friendly way to communicate with the machine. Popular operating systems are Microsoft Windows, Apple macOS, Linux and the Android system used in smartphones. Without an operating system, no application program can run, and the computer would be completely useless.
The operating system performs several important jobs at the same time. It manages memory, deciding which part of RAM each program can use. It manages files, keeping track of every document, folder and program on the disk. It manages devices, controlling the keyboard, mouse, printer and monitor through small programs called device drivers. It manages the processor, sharing the CPU among different programs so that everything runs smoothly. Finally, it provides the user interface, the part of the screen with which the user interacts to give commands.
The process of starting the computer is called booting. When the computer is switched on, a special program stored in ROM, called the bootstrap loader or BIOS, starts running. The BIOS checks the hardware with a test called the POST (Power On Self Test), and then loads the operating system from the hard disk into RAM. Once the operating system is loaded, the desktop appears and the computer is ready to use. Booting is of two types: cold boot, which happens when the computer is started by switching the power on, and warm boot, which happens when the computer is restarted with the restart command.
Operating systems can be classified by their user interface and by their processing style. By interface, there are Graphical User Interface (GUI) operating systems, which use icons, windows and menus, and Command Line Interface (CLI) operating systems, where the user must type text commands. By style, there are single-user single-task systems that allow one user to do one job at a time, single-user multitasking systems that allow one user to run several programs at once, and multi-user systems that allow many users to work at the same time, such as Linux and UNIX on servers.
In a GUI operating system, the first screen after booting is called the desktop. It contains small pictures called icons, which represent programs, files and folders. The taskbar at the bottom shows the programs that are currently running. The start button (in Windows) opens the start menu from which any program can be opened. The notification area at the right end of the taskbar shows the clock and the volume and network icons. The Recycle Bin is the place where deleted files are temporarily kept before they are removed permanently.
A file is a named collection of data stored on the disk, such as a letter, a picture or a program. A folder, also called a directory, is a container that holds files and other folders. Folders help in organising files neatly so that they can be found easily. A file has a name and an extension; the extension, such as .docx, .jpg or .exe, tells the operating system which program should open the file. The path is the address of a file, showing the sequence of folders from the drive to the file, for example C:\School\Class7\Essay.docx.
Windows is made by Microsoft and is the most widely used operating system for personal computers. It uses a desktop, taskbar and windows, and versions include Windows 10 and Windows 11. macOS is made by Apple for Macintosh computers and is known for its clean design and security. Linux is an open-source operating system, which means its source code is freely available, and it is used on servers and by programmers. Android and iOS are operating systems for mobile phones and tablets. Each operating system must match the hardware of the computer it runs on.
The Graphical User Interface lets the user interact by clicking on icons, menus and windows using a mouse. It is easy to learn and is used by most home users. The Command Line Interface requires the user to type instructions such as dir or mkdir in a text window. It is faster and uses less memory, and it is still used by system administrators and programmers. Both interfaces perform the same tasks, but the GUI is beginner-friendly while the CLI gives more direct control over the system.
| Function | What It Does |
|---|---|
| Memory management | Decides which program uses which part of RAM |
| File management | Organises and keeps track of files and folders |
| Device management | Controls hardware through device drivers |
| Processor management | Shares the CPU among running programs |
| User interface | Provides the screen through which the user gives commands |
| Type | Meaning | Example |
|---|---|---|
| Single-user single-task | One user, one program at a time | MS-DOS |
| Single-user multitasking | One user, many programs at once | Windows, macOS |
| Multi-user | Many users at the same time | Linux, UNIX |
| GUI based | Uses icons, windows and menus | Windows, Android |
| CLI based | Uses typed commands | MS-DOS, Linux terminal |
The operating system is the master program that manages memory, files, devices, the processor and the user interface. It boots the computer through the BIOS, provides a GUI or CLI for the user, and comes in different styles for single users and multi-user servers. Windows, macOS, Linux and Android are its most common examples. Now that we understand how the system is managed, we can begin using it to create documents with a word processor, the most widely used application software in the world.