Why Unix?

UNIX is an operating system (suite of programs), originally developed in 1969 at Bell Labs and has been under development ever since. UNIX is a very popular operating system for many reasons, including:

• multi user (multiple users can log in to a computer at the same time, and use concurrently the resources of that computer).

• multi-tasking (each user can perform many tasks at the same time).

• network-ready (built-in TCP /IP networking makes easy to communicate between computers).

• very powerful programming environments (free of the many limits imposed by other operating systems).

• robust and stable.

• scalable, portable, flexible.

• open source.

UNIX systems also have a graphical user interface (GUI) similar to Microsoft Windows which provides an easy to use environment. However, knowledge of UNIX is required for operations which aren't covered by a graphical program, or for when there is no windows interface available (for example, in a telnet session).

UNIX at a glance

UNIX consists of three main components: kernel, shell, and programs.

• KERNEL: hub of the operating system.

• SHELL: command line interpreter.

• PROGRAMS: collections of operations.

Each component has specific roles:

• KERNEL: it allocates time and memory to programs and handles the filestore and communications in response to system calls.

• SHELL: it interprets the commands the user types in and arranges for them to be carried out.

• PROGRAM: execute a set of predefined operations.

As an illustration of the way the shell and the kernel work together, suppose a user types the following command:

rm myfile 

Internally,

1. The shell searches the PATH environment variable for the file containing the program rm.

2. The shell requests to the kernel, through system calls, to execute the program rm on myfile.

3. When the process has finished running, the shell returns the UNIX prompt to the user, indicating that it is waiting for further commands.