An Operating System (OS) is the main system software that manages computer hardware and provides a working environment for applications and users. When you open Chrome, save a file, play music, connect Wi-Fi, print a document, or run several apps together, the operating system quietly manages the CPU, memory, files, devices and security behind the screen. It acts like a manager between applications and hardware. Windows, Linux, macOS, Android and iOS are common examples of operating systems. In this chapter, you will learn what an OS is, why it is needed, how it works, its main functions and services, the role of the kernel and system calls, and simple real-life examples.
What Is an Operating System?
An Operating System is system software that manages the hardware of a computer and provides services to application programs and users.
Think about your laptop or phone. It has a processor, RAM, storage, keyboard, screen, camera, speakers and many other parts. Applications such as a browser, music player or game cannot safely control all these parts on their own.
The operating system manages these resources and decides how they should be used.
In simple words, the OS is the software that makes the complete computer system usable.
Where Does the Operating System Sit in a Computer?
The operating system sits between applications and hardware. Applications ask the OS for services. The OS then uses the kernel and device drivers to communicate with hardware.
Why Do We Need an Operating System?
Imagine a computer with no operating system. Every application would need to know exactly how to control the processor, memory, disk, keyboard, display and every other device. Two programs could also try to use the same hardware at the same time and create problems.
The operating system solves this by providing one common layer that manages resources for all programs.
What Happens When You Open an App?
Suppose you click a web browser icon. It looks simple, but several OS tasks happen in the background.
You only see the browser window. The operating system handles the resource management behind it.
Main Functions of an Operating System
1. Process Management
A running program is called a process. The OS creates processes, schedules them, pauses them, resumes them and ends them when needed.
2. Memory Management
The OS keeps track of RAM and decides which process gets which memory area. It also protects one process from incorrectly accessing another process's memory.
3. File Management
The OS creates, opens, reads, writes, renames and deletes files. It also manages folders and permissions.
4. Device Management
The OS manages hardware devices through drivers and I/O control. Applications do not normally need to know every hardware detail.
5. CPU Scheduling
When many processes are ready to run, the OS decides which one should get CPU time and for how long.
6. Security and Protection
The OS controls login, user permissions, file permissions and access to important system resources.
7. Error Detection
The OS can detect many hardware and software errors and take action to prevent the whole system from failing.
8. Resource Allocation
The OS shares limited resources such as CPU time, RAM and devices among many programs.
Operating System Functions and Services: Are They the Same?
Students often use these two terms as if they mean exactly the same thing. They are closely related, but there is a useful difference.
OS Functions
Functions describe what the operating system manages internally, such as processes, memory, files, devices and security.
OS Services
Services describe the useful facilities the OS provides to users and application programs, such as program execution, file access and communication.
What Services Does an Operating System Provide?
| OS Service | What It Means | Simple Example |
|---|---|---|
| Program execution | Loads and runs a program | Opening a browser or calculator |
| I/O operations | Provides access to input/output devices | Reading keyboard input |
| File-system access | Creates, reads and writes files | Saving a document |
| Communication | Lets processes exchange data | Browser communicating with network services |
| Error detection | Detects and handles many errors | Reporting a failed disk operation |
| Resource allocation | Distributes CPU, memory and devices | Sharing CPU among many apps |
| Protection | Prevents unauthorized access | File permissions |
| Accounting | Tracks resource use | CPU time or storage usage records |
What Is the Kernel in an Operating System?
The kernel is the core part of an operating system that directly manages important hardware resources such as the CPU, memory and devices.
Applications
Browser, game, editor, compiler and other user programs ask the OS for services.
Hardware
CPU, RAM, storage and devices are controlled through the operating system and drivers.
You can think of the kernel as the most trusted and powerful part of the OS. It works close to the hardware.
Why Does a Computer Have User Mode and Kernel Mode?
If every application could directly control hardware and memory, one bad program could crash the entire system or access private data.
User Mode
Normal applications run with limited privileges. They cannot freely execute every sensitive hardware operation.
Kernel Mode
The operating system kernel runs with higher privileges and can perform sensitive operations required to manage the system.
What Is a System Call?
A system call is a controlled way for a user program to request a service from the operating system kernel.
For example, an application may need to open a file, create a process, read keyboard input or use the network. Instead of controlling hardware directly, it asks the operating system to perform the protected work.
See How the OS Handles a Request
Choose an action below. The visual shows the simple path from the application to the hardware.
Saving a File
What the OS is doing
How Does the Operating System Manage Running Programs?
A program stored on disk is just a file. When it starts running, it becomes a process.
How Does an Operating System Manage Memory?
RAM is limited. The operating system must keep track of which part of memory is free and which part is being used.
When an application starts, the OS gives it memory. When the application closes, that memory can be reused.
More advanced topics include paging, segmentation, virtual memory, page replacement and thrashing.
How Does the OS Manage Files?
The operating system gives users and applications a structured way to store data.
What Is Device Management in an Operating System?
The OS manages input and output devices such as keyboards, mouse devices, printers, disks, displays and network interfaces.
Device drivers help the operating system communicate with specific hardware. This allows applications to use devices without knowing all the low-level hardware details.
Operating System Examples From Daily Life
Examples of Operating Systems
| Operating System | Common Device | Simple Use |
|---|---|---|
| Microsoft Windows | Desktop and laptop computers | General personal and office computing |
| Linux | Servers, desktops and embedded systems | Development, servers and technical systems |
| macOS | Apple Mac computers | Desktop and laptop computing |
| Android | Smartphones and tablets | Mobile applications and communication |
| iOS | Apple iPhone | Mobile applications and communication |
Operating System vs Application Software
| Point | Operating System | Application Software |
|---|---|---|
| Main role | Manages system resources and provides a platform | Performs a user task |
| Examples | Windows, Linux, Android | Chrome, Word, VLC |
| Hardware access | Controls hardware through kernel and drivers | Usually requests OS services |
| Importance | Core system software | Runs on top of the operating system |
Main Goals of an Operating System
Common Student Confusions About Operating Systems
How to Write “What Is Operating System?” in an Exam
Definition answer
Define the OS as system software that manages hardware resources and provides services to users and application programs.
Definition + functions
Write the definition and explain process, memory, file and device management with one simple example.
Complete answer
Add OS goals, functions, services, kernel, system calls, user/kernel mode, diagram and real-life examples.
Easy exam memory trick
P M F D S = Process, Memory, File, Device, SecurityPractice Questions With Short Answers
1. What is an Operating System?
An Operating System is system software that manages hardware resources and provides services to users and application programs.
2. Why is an Operating System needed?
It is needed to manage hardware resources, provide a safe environment for programs and make the computer easy to use.
3. What is process management?
Process management is the OS function that creates, schedules, controls and terminates running programs.
4. What is memory management?
Memory management tracks RAM and decides how memory is allocated, protected and released.
5. What is a kernel?
The kernel is the core part of the operating system that directly manages important hardware resources.
6. What is a system call?
A system call is a controlled way for a user program to request a service from the operating system kernel.
7. Give two examples of operating systems.
Windows and Linux are two examples. Android, macOS and iOS are also operating systems.
8. What is the difference between user mode and kernel mode?
User mode has limited privileges for normal applications, while kernel mode allows the operating system to perform privileged system operations.
9. What is device management?
Device management is the OS function that controls and coordinates hardware devices using drivers and I/O mechanisms.
10. What are the main goals of an operating system?
The main goals are convenience, efficient resource use, protection, reliability and easy management of computer resources.
One-Minute Revision Sheet
Final memory line
The OS sits between applications and hardware and manages everything needed to make the computer usable.Frequently Asked Questions
What is an Operating System in simple words?
An Operating System is the main system software that manages computer hardware and provides services to applications and users.
What are the main functions of an Operating System?
The main functions include process management, memory management, file management, device management, security, error handling and resource allocation.
What is the difference between an OS and a kernel?
The operating system is the complete system software environment, while the kernel is its core component that directly manages important hardware resources.
What is a system call in OS?
A system call is a controlled request made by a program to the operating system kernel for services such as file access, process creation or device operations.
What are some examples of operating systems?
Common examples include Microsoft Windows, Linux, macOS, Android and iOS.
Why is an Operating System important?
An Operating System is important because it manages hardware resources, protects the system and provides a common platform on which applications can run.
Next Chapter: Types of Operating Systems
Next topic to study
After understanding what an Operating System does, the next step is to learn Batch, Multiprogramming, Time-Sharing, Real-Time, Multiuser and Multiprocessor Operating Systems.
This will help you understand how different operating systems are designed for different types of workloads.
