The Main Concepts that unites all versions of UNIX in Four Layers.
1. Application Programming
2. Shell
3. Kernel
4. Hardware.
Application Programming:
Is the layer where the commands and Programming are specified.
There are various command and
utilities which you would use in your day to day activities. cp, mv, cat
and grep etc. are few examples of commands and utilities. There are over
250 standard commands plus numerous others provided through 3rd party software.
All the commands come along with various optional options
Shell:
The shell
is the utility that processes your requests. When you type in a command at your
terminal, the shell interprets the command and calls the program that you want.
The shell uses standard syntax for all commands. C Shell, Bourne Shell and Korn
Shell are most famous shells which are available with most of the UNIX
variants.
Kernal :
The kernel
is the heart of the operating system. It interacts with hardware and most of
the tasks like memory management, task scheduling and file management.
Hardware :
It is the Configuration to the system. Contains the
Filesystem. All data in UNIX is organized into
files. All files are organized into directories. These directories are
organized into a tree-like structure called the filesystem.