Interview preparations: Operating System vs Kernel

Let’s talk about a kernel, an operating system, and all the differences between the two. I’ll explain what happens when you turn on your computer, and when you run programs.

Computers, smartphones, even cars — operating systems are everywhere. It’s worth knowing why we need this type of software, and what it does (other than taking up that precious disk space).

Almost all electronic devices run some kind of an operating system (source)

Why do we need an operating system?

Computers changed quite a bit since the twentieth century when they were invented. First computers could only run a single program until it finished… or crashed 😱

Each program used all of the available hardware and was responsible for all standard tasks a computer had to perform. For example, every program had to contain all necessary drivers.

Computers were not beginner friendly, to say the least.

Keeping track of what program was supposed to be run next was done by humans. Sometimes quite a bit of creativity was required:

At Cambridge University the job queue [a queue of programs waiting to be executed] was at one time a washing line from which tapes were hung with different colored clothes-pegs to indicate job-priority. (source)

And you’re complaining that your internet is too slow to stream Full HD videos, huh? 🤣

As the complexity of software, demand, and the number of users grew, it became too cumbersome and time-consuming to do all those things manually.

A program that could manage hardware, schedule program execution, and monitor resources was needed. That software should:

  1. Allow multiple applications to run at the same time. Hardware resources (for example, CPU time, network connections, opened files, and so on) should be shared “fairly” between those programs.
  2. Make sure that a buggy or malicious program cannot disrupt other applications.


Kernel is an always-running program that has complete control over everything in the system.

When you power on your device (for example, a computer or a smartphone) a small program called a boot loader is executed. Boot loader is a very small program — it starts the process of loading the operating system (including the kernel) and finishes immediately afterwards.

From then on, kernel is the king.

It decides what program will run next, and for how long.

It decides which memory can be used by each program.

If a program wishes to use any input/output device (like a mouse, a keyboard, and so on), it has to request access to that device from the kernel. If multiple programs want to access the same resource at the same time, kernel decides which program will get access first.

Kernel makes sure that a buggy or malicious program cannot disrupt other programs. It stops programs from monopolizing access to hardware, or modifying memory belonging to other processes. If a program misbehaves kernel will kill it 😨

Kernel is very powerful, but it only provides a basic level of control over the hardware it’s running on.

Kernel is the king

Operating system

In essence, a computer is just a tool we use to get things done. It has to be easy to use and user friendly. Hence, we need features such as a graphical user interface, a multimedia player, antivirus software, and so on.

An operating system (OS) consists of a kernel and additional software providing those features

What software is included in the operating system is entirely up to the creator of that OS. This makes defining an OS very difficult so it’s often described as “whatever you get when you order an operating system”.

For example, Windows 10 offers:

  • a sophisticated kernel
  • graphical user interface
  • firewall and antivirus software
  • web browser
  • multimedia player
  • small utility programs like a calculator, text editor, and so on

…and many other features.


A kernel is an essential part of an operating system. It’s an always-running program that is in control of everything in the system. It manages hardware resources and program execution.

An operating system consists of a kernel and some additional software making user’s interaction with his or hers device more pleasant. This might include graphical user interface, shell, web browsers, and so on.

Written on March 1, 2018