Structure of Unix Operating System

Unix is a multiuser, multitasking operating system that was developed by Bell Laboratories in 1969. In a multiuser system, many users can use the system simultaneously. A multitasking system is capable of doing multiple jobs. Each user interacts with their own shell instance in this type of operating system and can start applications as required.

An image that demonstrates the structure of the Unix operating system is −

Unix Structure

As seen in the image, the main components of the Unix operating system structure are the kernel layer, the shell layer and the application layer.

Details about these are given as follows −


The kernel provides a bridge between the hardware and the user. It is a software application that is central to the operating system. The kernel handles the files, memory, devices, processes and the network for the operating system. It is the responsibility of the kernel to make sure all the system and user tasks are performed correctly.


The program between the user and the kernel is known as the shell. It translates the many commands that are typed into the terminal session. These commands are known as the shell script. There are two major types of shells in Unix. These are Bourne shell and C Shell. The Bourne shell is the default shell for version 7 Unix.

The character $ is the default prompt for the Bourne shell. The C shell is a command processor that is run in a text window. The character % is the default prompt for the C shell.


The applications and utility layer in Unix includes the word processors, graphics programs, database management programs, commands etc. The application programs provide an application to the end users.

For example, a web browser is used to find information while gaming software is used to play games. The requests for service and application communication systems used in an application by a programmer is known as an application program interface (API).