The history of UNIX and Linux

The history of UNIX starts back in 1969. At that time at Bell Labs Ken Thompson, Dennis Ritchie and others started playing with a little-used PDP-7 system. They wanted to create a new time sharing multi user multi tasking operating system, based on earlier work on a system called MULTICS.

The first UNIX version was written entirely in PDP assembler, which made it highly dependent on the hardware. In 1973 UNIX was rewritten in the new C programming language (also created by Dennis Ritchie and his friend Brian Kernighan). This made UNIX portable to multiple types of computer hardware.

In 1975 version 6 was the first to be widely available outside of Bell Labs (later AT&T) and in 1982 UNIX was licensed to a large amount of computer manufacturers, including Sun Microsystems (Solaris) and Hewlett Packard (HP-UX). All these vendors started to market their own UNIX versions (adapted to their own hardware and needs), that were based on the original UNIX source code. Customers found that, although UNIX systems were available everywhere, they seldom were able to interwork in an easy way. The trademark UNIX applied to a multitude of different, incompatible products.

In early 1993, AT&T sold it UNIX System Laboratories to Novell which was looking for a heavyweight operating system to link to its NetWare product range. In 1995 SCO bought the UNIX Systems business from Novell, and UNIX system source code and technology continues to be developed by SCO.

UNIX had been closely linked with open systems. X/Open, now part of The Open Group, continues to develop and evolve the Single UNIX Specification and associated brand program on behalf of the IT community.

UNIX is still one of the major operating systems, in many variants (HP's HP-UX and Tru64, IBM's AIX, Sun Microsystem's Solaris, etc.). The increasing popularity of Linux however (which runs on standard PC hardware) has gradually moved popularity from UNIX towards Linux.


In 1987 Andrew Tanenbaum, who was a professor of computer science at the Vrije Universiteit, Amsterdam in the Netherlands, wrote a clone of UNIX, called MINIX (MIni-uNIX), for the IBM PC. He wrote MINIX especially for his students to teach them how an operating system worked. Tanenbaum wrote a book that not only listed the 12,000 lines of MINIX source code, but also described each part of the source code in detail, including the theory about why it was programmed the way it was. I strongly recommend reading his book ('Operating Systems: Design and Implementation' - see the appendix for the details). It provides a wealth of knowledge on process control, memory management, file systems, etc.

Linus Torvalds, at the time a student at the University of Helsinki, studied MINIX in an operating systems course and was sufficiently impressed that he bought a PC to run it. In 1991Torvalds wanted to explore the multitasking possibilities of the new 80386 CPU and decided to create a small multitasking, multi-user operating system with the help of the Internet community. Using USENET he asked developers on the Internet to help him with the development.

After that initial post things went fast. Because of the open source nature of Linux many developers contributed with kernel patches, device drivers and additions like multilingual keyboards, floppy disk drivers, support for VGA, EGA, Hercules, and much more.

It is important to understand that Linux is merely an operating system kernel. Linux distributions as we know them today consist of the Linux kernel and drivers and the GNU project’s applications, libraries, compilers and tools.

The GNU project (GNU is a recursive acronym for “GNU's Not Unix!”) was launched in 1983 by Richard Stallman to develop a free complete UNIX-like operating system. The GNU project developed of a large collection of libraries, applications, compilers and tools. By 1990 the GNU project had either found or written all the major components of the UNIX-like system except one - the kernel. Combining Linux with the almost-complete GNU system resulted in a complete operating system: the GNU/Linux system.

Linux and the GNU tools are licensed under GNU General Public License, ensuring that the source codes will be free for all to copy, study and to change.

Soon, commercial vendors moved in. Linux itself was, and is free. What the vendors did was to compile up various software and gather them in a distributable format. Red Hat, SuSe, Caldera and Debian are some of the best known Linux distributions. Extended with Graphical User Interfaces (like X-window System, KDE, GNOME) the Linux distributions became very popular.

Today Linux is a very mature operating system used in mission critical systems and distributes systems (to a large degree the Internet is based on Linux technology). Companies like Red Hat and Novell (who purchased SuSe) provide professional Linux distributions including support contracts.

This entry was posted on Vrijdag 07 Januari 2011

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