Unix Operating System:

Unix is a popular and powerful multi-user operation system. It is a set of programs that acts as link between the computer and the user. In 1969, it was developed by Dennis Ritchie and Ken Thomson, both were working at AT&T Bell lab.

Unix system organization:

User can control and working with hardware through Shell and Kernel.

The Shell:

Users communicate with the kernel through a program known as the shell. The shell is a command interpreter also called as mediator, which interprets the commands that user give and convey to kernel to execute. There are 3 types of shells.

1)Bourne shell

Bourne shell is the default Unix shell that was developed at AT&T.  It is a command line interpreter for computer operating system. The Bourne shell family includes the Bourne, Korn shell, bash, and zsh shells. It is a fully programmable environment with the power of a full programming language at its command.

2)Korn shell

The Korn Shell (ksh) is an interactive command interpreter that has the best features of both the C Shell and the Bourne Shell. It was designed and developed by David G. Korn at AT&T Bell Laboratories. The first line in a Korn shell script is the shell itself. It is denoted as follows: #!/bin/ksh. It is almost entirely upwardly compatible with the Bourne shell and  it includes the best features of the C shell as well as several advantages of its own.

3)C shell

The C shell is a command processor typically run in a text window, allowing the user to type commands. It is created by Bill Joy at the University of California at Berkeley as an alternative to UNIX’s original shell, the Bourne shell . The C shell was invented for programmers who prefer a syntax similar to that of the C programming language.

It has introduced many improvements over the Bourne shell designed for interactive use. These includes history, editing operations, a directory stack, job control and tilde completion.

The Kernel:

The kernel, which is critical to the operation of the OS, is loaded into Random Access Memory (RAM) by the boot loader, where it remains memory resident for as long as the machine remains powered on. It has various functions. It manages files, carries out all data, transfer data between file system. Also it scheduling the program running and allocation of CPU,etc.

Unix file system:

The Unix file system is a methodology for logically organizing and storing large quantities of data such that the system is easy to manage. In Unix all utilities, applications, data are stored as files. Unix file system begins with ‘/’ (root) directory. Under the ‘/’ , there are other several directories called bin, lib, user, dev, temp and etc.

• bin – short for binaries, this is the directory where many commonly used executable commands reside

• lib – contains all library files

• dev – contains device specific files

• usr – also contains executable commands

• tmp – storage for temporary files which are periodically removed from the filesystem

• etc – contains system configuration files