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07 September 2015

UNIX AND LINUX a short history

Unix is an old operating system, dating back to 1969. Its earliest incarnation, known as MULTICS, was developed for a single platform. It was developed by AT&T Bell Labs. Two of the employees, Dennis Ritchie and Ken Thompson, wanted to revise MULTICS to run as a platform-independent operating system. They called their new system Unics, with its first version being written in the assembly language of the DEC PDP-11 computer so that it was not platform-independent.
They rewrote the operating system in the C programming language (which Ritchie developed in part for Unix) to make it platform independent. This version they named Unix.
Numerous versions of Unix were released between 1972 -- early 1980's including a version that would run on Intel 8086-based computers such as the early IBM PC and PC-compatible computers.
Unix was not a free operating system. In spite of it being implemented as a platform-independent operating system, it was not available for all hardware platforms.
In 1983, Richard Stallman of MIT began the GNU Project, an effort to complete a Unix-like operating system that was both free and open source. GNU stands for GNU’s Not Unix, an indication that GNU would be a Unix-like operating system but separate from Unix. His goal was to have anyone and everyone contribute to the project. He received help from programmers around the world who freely contributed to the GNU operating system, which they wrote from scratch. Although a completed version of GNU was never released, the approach taken was to lead to what we now call the open source community.
Stallman formed the Free Software Foundation (FSF) and defined the GNUs General Public License (GPL).
At around the same time as the initiation of the GNU Project, researchers at the University of California Berkeley developed their own version of Unix, which was given the name BSD (Berkeley Standard Distribution) Unix. This version includes networking code to support TCP/IP so that these Unix computers could easily access the growing Internet.
In time, BSD 4.2 would become one of the most widely distributed versions of Unix.
The result of several competing forms of Unix led to what some have called the “Unix Wars.” The war itself was not restricted to fighting over greater distribution. In 1992, Unix System Laboratories (USL) filed a lawsuit against Berkeley Software Design, Inc and the Regents of the University of California. The lawsuit claimed that BSD Unix was built, at least partially, on source code from AT&T’s Unix, in violation of a software license that UC Berkeley had been given when they acquired the software from AT&T. The case was settled out of court in 1993.
By 1990, the Open Software Foundation (OSF), members of the open source community had developed standardized versions of Unix based on BSD Unix.
Today, there are still many different distributions of Unix available which run on mainframe, minicomputers, and servers.

In 1991, a student from Finland, Linus Torvalds, was dissatisfied with an experimental operating system that was made available through an operating systems textbook of Andrew Tanenbaum. The operating system was called Minix. It was a scaled down Unix-like operating system that was used for educational purposes. Torvalds decided to build his own operating system kernel and provide it as source code for others to play with and build upon(Torvalds has claimed that had the GNU project kernel been available, he would not have written his own). Early on, his intention was just to explore operating systems. Surprisingly, many programmers were intrigued with the beginnings of this operating system, and through the open source community, the operating system grew and grew.
The development of Linux in many ways accomplished what Stallman set out to do with the GNU project. Stallman and many in the FSF refer to Linux as GNU/Linux as they claim that much of Linux was built on top of the GNU project code that had been developed years earlier. According to some surveys, roughly 75% of Linux has been developed by programmers who work for companies that are investing in Linux. The GPL causes many of these programmers to publish their code rather than keeping the code proprietary for the companies they work for. Additionally, 18% of the code is developed strictly by volunteers who are eager to see Linux grow.
Today, Linux stands on its own as a different operating system from Unix. Linux is freely available in source code and the open source community continues to contribute to it. And like Unix, there are many distributions(many many more than Unix distros really).
Unlike Unix, however, Linux’s popularity is far greater because, while Unix can run on personal computers, Linux is geared to run on any platform and is very effective on personal computers.
Although there are dozens of dialects of Unix, there are hundreds of different Linux distributions. Navigating between the available dialects can be challenging. Nearly all of the dialects can be categorized into one of four ancestor paths.
  • Debian: This branch includes the very popular Ubuntu which itself has spawned dozens of subdialects. Another popular spin-off of Debian is Knoppix.
  • Red Hat: There are as many or more subdialects of Red Hat as Debian. The most popular subdialect is Fedora. Another popular descendant is Mandrake and another is CentOS. Another distribution that is increasing in popularity is Scientific Linux, produced by Fermi National Accelerator Laboratory and CERN.
  • SLS/Slackware: This branch was first produced by a German company which led to SuSE Linux. Although there are dozens of spin-offs of SLS/Slackware, it is far less popular than either Debian or Red Hat.
  • Miscellany: There are dozens of dialects that either led nowhere or have few successors.
Linux and Unix operating systems are partially or completely POSIX conforming. POSIX is the Portable Operating System Interface, a set of standards that operating system developers might attempt to target when they implement their systems. POSIX defines an Application Programming Interface (API) so that programmers know what functions, data structures, and variables they should define or utilize to implement the code they are developing for the operating system.
In the development of Linux, the POSIX API has been used to generate a standard called the Linux Standard Base (LSB).
Anyone implementing a dialect of Linux who wishes to include this standard knows what is expected by reading the LSB. The LSB, among other things, defines the top-level directory structure of Linux and the location of significant  Linux files such as libraries, executables, and configuration files, a base set of Linux commands and utilities to be implemented, and implementations for such programs as gcc, the Gnu's C compiler.
Thus, underlying most dialects of Linux, you will find commonalities. In this way, learning one version of Linux is made easier once you have learned any other version of Linux.


Linux with Operating System Concepts by Richard Fox
isbn:9781482235906, goodreads:20792170

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