Shell, Kernel, and API Explained: The Core Layers of an Operating System

Regular users don’t actually bother about how everything functions in their machines. We tend to switch our computer and use it for the needed purpose, but there are lots of processes behind the scenes. The major components of any OS are the shell and kernel.

Initially, these 2 terms might sound very technical; however, they are rather straightforward and really understandable. Here, in this article, we will guide you through the major differences between these 2 terms and explain why they are important for any OS.

Core Operations of the Kernel

The kernel is a core element of the OS, and it directly interacts with the machine’s hardware. The major role of this part is to connect hardware with the applications in such a way that software apps can work without any issues related to the storage, memory, and devices.

That means when you are playing a game or just browsing on your computer, this component is necessary for the smooth functioning and management of the resources. In any OS, the process is connected with the following elements: memory (data, heap, stack), Process Control Block, and scheduling metadata.

Major functions of the kernel

• Management of memory. This means it is needed for the RAM allocation to apps and reclaiming it when it isn’t needed.
• Management of processes. There are lots of tasks that are running on your machines even when you have switched only one app. So, kernel functions by dividing CPU time and creating the right order.
• Management of the devices. Each device, such as a printer, keyboard, GPU, or hard drive, should somehow interact with the OS. For the purpose of proper interaction between the software and hardware, special drivers are used.
• Protection and security. Kernels also function by ensuring that certain programs don’t have access to the restricted hardware and memory. Moreover, it helps with process isolation.
• Dealing with the file system. It helps with creating a specific structure for the retrieval and storage of the data. For instance, kernel functions for the saving, opening, and deleting of the files behind the scenes.

To get a more practical explanation, let’s review the process of music player functioning. The kernel allocated necessary memory for the app, then checks whether CPU processes it, interacts with the audio device, and then manages the file access.

Types of Kernels

Based on the OS, various types of kernels are used, such as:

• Microkernel. Here, only necessary services function on the kernel, and others function separately (Minix).
• Monolithic. All the services function in one huge block of code (Linux).
• Hybrid. Unites features of microkernel and monolithic (Windows).

Categories of Shells

The shell is an interface that functions between the kernel and the user. It works by taking direction from the end user and passing it to the kernel, and then sharing the end result with the user. All the processes in the kernel are unnoticeable for the user, while the shell is visible, because you directly interact with it.

Types of shells

• Command-line shell (CLI). It functions with the help of commands. The main examples are Zsh, Bash, and PowerShell. This type might look very challenging at first, but it is actually helpful for the admins, developers, and ordinary users.
• Graphical shell (GUI). This type is considered the most standard option, where there are icons, windows, and various menus. The major examples are Finder, Windows Explorer, and GNOME.    

Major differences between Kernel and Shell

The interaction process between Kernel and Shell

For a better understanding of the process, let’s discuss one specific example:

1. Action of the user – clicking on the file in Windows.

2. Shell – understand the command and redirect it into the kernel.

3. Kernel – gets the file from the storage, allocates memory, and prepares necessary information.

4. Shell – output the needed content on the screen.

Summary

To sum up, the shell is an interface that helps users to interact with the kernel. Whereas the kernel is dealing with the interaction between the hardware and the software. Both these elements are extremely important, and they are silently working to make the user experience smoother.