1960s: MIT, GE and Bell Labs develop an operating system for "mainframes" (the big computers at that time): multics.
1969: Ken Thompson and Dennis Ritchie (Bell Labs) develop unics for the DEC PDP-7. Thie idea is to completely rewrite the Multics operating sstem by keeping only what is simple and interesting, and by leaving out a maximum of the complexity.
1970: Brian Kernnighan joins the project. Unics becomes Unix
1972-1973: invention of the C language by Dennis Ritchie and Brian Kernnighan. Rewrite of UNIX in C. Before that time, operating systems were written exclusively in assembly (=machine language).
There does not exist one UNIX but Unixes.
At the beginning, UNIX belonged to AT&T (which owns Bell Labs) who sold operating systems for different machines. Machine vendors (IBM, DEC, etc.) have modified the original Unix to adapt it to their hardware. To the other side, universities like Berkeley have also worked on Unix to improve the software part.
1983: Richard Stallman (MIT) announces the GNU project ("GNU's Not Unix"): build a UNIX operating system composed of free software. A software is said to be free (free software) if the people who receive a copy of it have:
- the freedom to use it for any purpose (= commercial or not)
- the freedom to study it and to make any changes
- the freedom to redistribute as many copies as they want if they want
- the freedom to improve the program and distribute these improvements so that everyone can benefit from them We speak of open source or free movement. Richard Stallman and the Free Software Foundation have published a license specific for free software: GNU (General Public License) which forces anyone who distributes modifications of a GNU program to distribute these changes under the same GNU license. We then speak of copyleft in opposition to copyright.
1991: Linus Torvalds proposes a UNIX kernel under GNU license: Linux (Linus' UNIX)