1. The Linux operation system consist of three main sofware components, as shown in the following diagram:



    KERNEL

    The core of the Linux system is the kernel, is the operating system program. The kernel controls the resources of the computer , allotting them to different user and tasks. It interacts directly with the hardware. Because the kernel communicates directly  with the hardware., the parts of the kernel must be customized to the hardware features of each system. However, the kernel does not interact directly with a user. Instead, the login process stars up a separate, interactive program called the IshellI for each user.

    SHELL

    Linux has a simple user interface called the shell that has the power to provide the services that a user wants. It protects the user from having to know the intricate hardware details. The features of the shell will be discussed in subsequent sessions.


    Linux Utilities and Application Program

    The Linux utilities or commands are collection of programs that service day-yo-day processing requirements. These programs are invoked through the sell, which itself  another utility. A part from the utilities provided as part of the Linux operation system, System (DBMS), word processors, and various other programs are available from independent software vendors.

    Comparing Linux with UNIX

    Linux developed keeping Unix ass a reference model. Therefore, the basic architecture and most of the features of Linux and UNIX are the same. In fact, Linux is also considered as another version of Unix. The main difference between Linux and Unix is that Linux is available free of charge. Various distributors of Linux do charge a price but the price is low as compared  to other operating systems. What you get is a full-blown server operating system without any licensing issues. Linux comes with all the development tools you cold possibly require, such as awk, perl, and phyton , most of which are free. In addition, web servers, such as Apache, and browsers, such as Netscape provide their version for Linux, again free of charge.

    The UNIX operating system requires at least 500 MB of hard disk space. On the other hand, Linux can be installed on a computer having 150 MB of hard disk space and can run on 8 MB of RAM.

                                    FEATURE                    LINUX                                            Unix
                                 Shells                        bash, pdksh,tcsh,zsh                       Bourne, Korn, C
                                 available                   ash
                                 vaariants                   Red Hat, Caldera,                            AT & T, MULTICS, BSD,  
                                                                                                                     SCO
                                                              Debian, LinuxPPC, SuSE               HP-Ux, IRIX, Ultrix, XENIX,
                                                                                                                    Sun Solaris
                                  Licensing             Freely distributed                            Expensive Licensing
                                  
                                                        Comparison between Linux and Unix     

    Distributors of Linux     

    Many distributors provide Linux. All the distributors use the Linux kernel, which is controlled  by Linus Torvalds. These distributors add their own utilities and Application and sell the utilities as a customized package. Red hat, Debian, and Slackware, are freely usable and after you by them., you can sell them yourself. (note that not all the package coming with these distributors are free, some have to be bought with a license). As a result, many other distributors take them as the base for adding utilities. Some of the popular distributors have been mentioned below. More information on the distributors can be found from their web sites.

    Mandrake

    MandrakeSoft offers the power and stability of the Linux to both individual and enterprise users in a user-friendly environment. It contains more than 2300 high-quality applications including a complete office Suite of programs and a complete installations supports.
    Web site: http://www.mandrakelinux.com

    Debian

    Debian is among earliest distributions of Linux. It utilizes the Linux kernel.
    However, Debian is designed to accommodate other kernel as well. It is available for free. It offer precompiled software bundled with more than 8000 packages and an easy installation procedure .
     Web site :  http: //www.debian.org


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  2. History Of Linux

         Before  the advent of UNIX, most system were single-user system. there systems were fast but were not portable because they were written in machine-level language, which was specific to the computer on which it was written. In 1965, Bell Labs and Massachusetts Institute  of Technology (MIT) along with General Electric took part in the development of one of the first multi-use computer systems called multiplexed Information and Computing Service (Multics). Ken Thomson and Dennis Ritchie, two Bell Labs engineers, worked on this project until 1969. Later, they developed an operation system, Uniplexed information and Computing Service (Unics), which was similar to the Multics operation system. The name Unics was then changed to UNIX.
         In 1973 Ken Thomson and Dennis Ritchie re-wrote Unix using the C programming language. Around 1974, UNIX was licensed to universities for educational purposes and, a few later, was made available Commercially.
         In 1976-77, Ken Thomson took a six-month sabbatical from Bell Labs to teach as a visiting professor at the computer Science Department  at the University of California Berkeley (UCB). What he taught, of course, was the UNIX system. It was an instant hit,  in the world spread quickly throughout the academic community. When Thompson returned to Bell Labs, students and professors at Berkeley continued to enhance UNIX. Eventualy, many of these enhancements were incorporated into what came to be known as Berkeley Software Distributor (BSD) Version 4.2.
        Minix was another miniature version of UNIX, mainly used as a teaching aid in universities and colleges. It  was a Free UNIX clone available with all the source code. Due to its small size, micro kernel-based design, and ample documentation, it was well suited to people who wanted to run a UNIX-like system on their personal computer.
        IT is interesting to note that MS DOS was created much later than UNIX, by which time the industry had begun to accept UNIX as the standar operation system. Therefore, UNIX features have influenced the design of MS DOS.
        Many vendors, such as Sun,IBM, and Hewlett-packard, purchased the source code of UNIX. They developed their own version of UNIX. This resulted in many differences between various versions. To avoid the confusion, some standards called portable Operation system for the UNIX environment (POSIX), were outlited. POSIX was a set of standards that enabled software to run on different UNIX-basded operating systems without changes to the source code.
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