What is an Operating System?

Before learning processes, threads, memory, scheduling, or system calls, we should first understand one basic question:

What is an Operating System, and why do we need it?

An Operating System (OS) is system software that sits between applications and hardware.

It manages the computer's resources and gives programs a safe, controlled way to use them.

Examples of operating systems:

• Windows
• macOS
• Linux
• Android
• iOS

Why does an Operating System exist?

Imagine you open Chrome, VS Code, Spotify, and a terminal at the same time.

All of them need hardware resources:

• CPU to execute instructions
• RAM to store running data
• Disk to read and write files
• Network to send and receive data
• Keyboard, mouse, screen, speakers, and other devices

Now the question is:

Who decides which program gets the CPU, how much memory it gets, and whether it is allowed to access a file or device?

That is the job of the Operating System.

The OS exists to:

• Run multiple programs safely.
• Share CPU time between programs.
• Allocate and protect memory.
• Manage files and storage.
• Control hardware devices.
• Provide security and permissions.
• Give applications common APIs through system calls.

In simple words:

The OS is the manager of the computer. Applications ask, and the OS controls access to hardware.

What happens if there is no Operating System?

Without an OS, every program would need to handle hardware directly.

For example, if you wrote a simple music player, you would also need to write code to:

• Talk directly to the sound card.
• Read files from disk.
• Manage memory manually.
• Handle keyboard and mouse input.
• Decide how CPU time is shared.
• Prevent other programs from corrupting your data.

That would make application development extremely difficult.

Even worse, if multiple programs ran together without an OS:

• One program could overwrite another program's memory.
• One program could take full control of the CPU.
• Two programs could write to the same device at the same time.
• There would be no proper file permissions.
• A crashing program could bring down the whole machine.

So without an OS, the computer would not feel like a usable general-purpose machine.

It would be closer to a raw hardware board where each program must manage everything by itself.

Simple Summary

An Operating System is the software layer that manages hardware and provides services to applications.

It exists because applications should not directly fight over CPU, memory, files, network, and devices.

The OS makes the computer usable, safe, fair, and easier to program.