Unix - Introduction to Unix

What Is UNIX?

UNIX is an operating system developed in the Bell Laboratories of AT&T and is an example a multi-tasking, multi-user operating system. It provides its users with: program development tools; electronic communications facilities, such as an electronic mail; text editors and text formatters. There are also many development tools available as standard within the UNIX operating system that other operating systems require as add-ons.
UNIX Shells

UNIX provides a series of shells. You, the user, are on the outermost shell; the second layer is called the shell, this interprets your commands and passes the instructions to the operating system proper; the third layer is the kernel which handles the interaction between the shell and the hardware; and the fourth layer is the hardware itself. The standard shell is the Bourne Shell which was designed for general purpose use. It is relatively small, and efficient, but lacks certain facilities, such as a command history and aliasing. Two popular enhanced shells are the C Shell and the Bourne Shell. The C shell is less efficient compared to the Bourne and Korn shells; the Korn shell is larger than the Bourne shell but it is more efficient because of its built-in functions.

The shell interacts with the UNIX's Kernel which is heart of the operatiing system. The kernel is the bridge between the application packages and the hardware it is running on.
 

What Is An Operating System?

All computers require an operating system which is a collection of instructions, programs and procedures which allow a computer to control the resources that are available. An operating system undertakes all the management chores of the computer: the management of its memory; the handling of disk and/or tape storage facilities; the management of printers, plotters and other peripheral devices -- including its users connected via terminal lines.

All operating systems share the task of translating commands, in the form of pseudo-English words, into instructions the computer can understand. Users type their instructions on a line -- called the command line. The difference between most operating systems, as far as users are concerned, are the wide variety of commands across operating systems that perform the same function. For example: dir, catlist, ls and *. are all examples of commands that list the names of files on the current storage device, in the current working directory.

Most personal computers have a single-user operating system, for example, MS-DOS on IBM PCs and Finder on Apple Macintoshes. These machines can only be used by one user at any one time to perform a single task, for example running a word processing package or a spreadsheet program. Larger computers can support several users performing several tasks and these machines need a more sophisticated multi-user and multi-tasking operating system.

Source:http://www.le.ac.uk/oerresources/bdra/unix/page_06.htm