Is Linux Unix??

[Clinton MacDonald]

Ed:

Ed Sutherland wrote:
> This has probably been answered before, but how do Unix (*BSD), Linux 
> and Darwin compare? If I'm running Linux, am I running Unix?

The history of Unix (and Unix-like operating systems) is complex and
varied. What follows is my own vague recollections of what I have heard
and read, and almost certainly contains oversimplifications and
inaccuracies.

Officially, if you are running Linux, you are *not* running Unix. Unix
is a proprietary (and usually expensive) operating system descended from
the one started at Bell Labs in 1969 by Dennis Ritchie, Kenneth Thompson
and others. Unix was first written to run on the PDP-7 computer in the
days of timeshared terminals. However, one of the key features that made
Unix revolutionary was that it was written in the C programming language
instead of in direct machine code. This made it the first portable
operating system, and this was a major revolution.

<http://www.bell-labs.com/history/unix/>

BSD ("Berkeley Software Distribution") Unix is a more direct descendant
of Unix that was rewritten to remove commercial code. Several versions
of BSD Unix (FreeBSD, OpenBSD, etc.) now exist that are open source.

(There are some funny stories of how BSD Unix was distributed
on-the-sly. Since early versions of BSD Unix contained lots of
copyrighted code, it was not officially available for distribution
without extremely high licensing fees, which most educational
institutions could not afford. Therefore, whenever Ritchie or Thompson
visited universities to give talks, they would "accidentally" leave the
system tapes lying around, which were "accidentally" copied by eager
graduate students.)

Linux is a much newer operating system that was written by Linux
Torvalds when he was a graduate student in Finland (ca. 1991). Linux
(more accurately GNU/Linux) was designed as a Unix *work-alike*
operating system, but was written with no knowledge of the actual Unix
code (the ongoing SCO court battles contend that copyrighted Unix code
has crept into the Linux -- almost certainly false, though time will tell).

Darwin, the "bottom" layer of Apple's Mac OS X, is derived from BSD Unix
and the Mach microkernel. Avie Tevanian, Apple's senior software
engineer, contributed greatly to the Mach microkernel when he was
obtaining his Ph. D. from Carnegie-Mellon University, then during his
time at NeXT Computer. When Apple bought NeXT, they bought Steve Jobs,
Avie Tevanian, and the Mach/BSD technology on which the NeXT operating
system was based. Not a bad deal.

Best wishes,
Clint

-- 
Dr. Clinton C. MacDonald | <mailto:clint DOT macdonald AT sbcglobal DOT net>