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Unix history
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PostPosted: Wed 18 Jan 2012, 19:40    Post subject:  Unix history
Subject description: IEEE article

The Strange Birth and Long Life of Unix
The classic operating system turns 40, and its progeny
By Warren Toomey
ieee spectrum
December 2011

They say that when one door closes on you, another
opens. People generally offer this bit of wisdom just to
lend some solace after a misfortune. But sometimes it's
actually true. It certainly was for Ken Thompson and the
late Dennis Ritchie, two of the greats of 20th-century
information technology, when they created the Unix
operating system, now considered one of the most
inspiring and influential pieces of software ever

A door had slammed shut for Thompson and Ritchie in
March of 1969, when their employer, the American
Telephone & Telegraph Co., withdrew from a collaborative
project with the Massachusetts Institute of Technology
and General Electric to create an interactive time-
sharing system called Multics, which stood for
"Multiplexed Information and Computing Service." Time-
sharing, a technique that lets multiple people use a
single computer simultaneously, had been invented only a
decade earlier. Multics was to combine time-sharing with
other technological advances of the era, allowing users
to phone a computer from remote terminals and then read
e-mail, edit documents, run calculations, and so forth.
It was to be a great leap forward from the way computers
were mostly being used, with people tediously preparing
and submitting batch jobs on punch cards to be run one
by one.

Over five years, AT&T invested millions in the Multics
project, purchasing a GE-645 mainframe computer and
dedicating to the effort many of the top researchers at
the company's renowned Bell Telephone Laboratories--
including Thompson and Ritchie, Joseph F. Ossanna,
Stuart Feldman, M. Douglas McIlroy, and the late Robert
Morris. But the new system was too ambitious, and it
fell troublingly behind schedule. In the end, AT&T's
corporate leaders decided to pull the plug.

After AT&T's departure from the Multics project,
managers at Bell Labs, in Murray Hill, N.J., became
reluctant to allow any further work on computer
operating systems, leaving some researchers there very
frustrated. Although Multics hadn't met many of its
objectives, it had, as Ritchie later recalled, provided
them with a "convenient interactive computing service, a
good environment in which to do programming, [and] a
system around which a fellowship could form." Suddenly,
it was gone.

With heavy hearts, the researchers returned to using
their old batch system. At such an inauspicious moment,
with management dead set against the idea, it surely
would have seemed foolhardy to continue designing
computer operating systems. But that's exactly what
Thompson, Ritchie, and many of their Bell Labs
colleagues did. Now, some 40 years later, we should be
thankful that these programmers ignored their bosses and
continued their labor of love, which gave the world
Unix, one of the greatest computer operating systems of
all time.

The rogue project began in earnest when Thompson,
Ritchie, and a third Bell Labs colleague, Rudd Canaday,
began to sketch out on paper the design for a file
system. Thompson then wrote the basics of a new
operating system for the lab's GE-645 mainframe. But
with the Multics project ended, so too was the need for
the GE-645. Thompson realized that any further
programming he did on it was likely to go nowhere, so he
dropped the effort.

Thompson had passed some of his time after the demise of
Multics writing a computer game called Space Travel,
which simulated all the major bodies in the solar system
along with a spaceship that could fly around them.
Written for the GE-645, Space Travel was clunky to play-
and expensive: roughly US $75 a game for the CPU time.
Hunting around, Thompson came across a dusty PDP-7, a
minicomputer built by Digital Equipment Corp. that some
of his Bell Labs colleagues had purchased earlier for a
circuit-analysis project. Thompson rewrote Space Travel
to run on it.

And with that little programming exercise, a second door
cracked ajar. It was to swing wide open during the
summer of 1969 when Thompson's wife, Bonnie, spent a
month visiting his parents to show off their newborn
son. Thompson took advantage of his temporary bachelor
existence to write a good chunk of what would become the
Unix operating system for the discarded PDP-7. The name
Unix stems from a joke one of Thompson's colleagues
made: Because the new operating system supported only
one user (Thompson), he saw it as an emasculated version
of Multics and dubbed it "Un-multiplexed Information and
Computing Service," or Unics. The name later morphed
into Unix.

Initially, Thompson used the GE-645 to compose and
compile the software, which he then downloaded to the
PDP-7. But he soon weaned himself from the mainframe,
and by the end of 1969 he was able to write operating-
system code on the PDP-7 itself. That was a step in the
right direction. But Thompson and the others helping him
knew that the PDP-7, which was already obsolete, would
not be able to sustain their skunkworks for long. They
also knew that the lab's management wasn't about to
allow any more research on operating systems.

So Thompson and Ritchie got creative. They formulated a
proposal to their bosses to buy one of DEC's newer
minicomputers, a PDP-11, but couched the request in
especially palatable terms. They said they were aiming
to create tools for editing and formatting text, what
you might call a word-processing system today. The fact
that they would also have to write an operating system
for the new machine to support the editor and text
formatter was almost a footnote.

Management took the bait, and an order for a PDP-11 was
placed in May 1970. The machine itself arrived soon
after, although the disk drives for it took more than
six months to appear. During the interim, Thompson,
Ritchie, and others continued to develop Unix on the
PDP-7. After the PDP-11's disks were installed, the
researchers moved their increasingly complex operating
system over to the new machine. Next they brought over
the roff text formatter written by Ossanna and derived
from the runoff program, which had been used in an
earlier time-sharing system.

Unix was put to its first real-world test within Bell
Labs when three typists from AT&T's patents department
began using it to write, edit, and format patent
applications. It was a hit. The patent department
adopted the system wholeheartedly, which gave the
researchers enough credibility to convince management to
purchase another machine-a newer and more powerful
PDP-11 model-allowing their stealth work on Unix to

During its earliest days, Unix evolved constantly, so
the idea of issuing named versions or releases seemed
inappropriate. But the researchers did issue new
editions of the programmer's manual periodically, and
the early Unix systems were named after each such
edition. The first edition of the manual was completed
in November 1971.

So what did the first edition of Unix offer that made it
so great? For one thing, the system provided a
hierarchical file system, which allowed something we all
now take for granted: Files could be placed in
directories-or equivalently, folders-that in turn could
be put within other directories. Each file could contain
no more than 64 kilobytes, and its name could be no more
than six characters long. These restrictions seem
awkwardly limiting now, but at the time they appeared
perfectly adequate.

Although Unix was ostensibly created for word
processing, the only editor available in 1971 was the
line-oriented ed. Today, ed is still the only editor
guaranteed to be present on all Unix systems. Apart from
the text-processing and general system applications, the
first edition of Unix included games such as blackjack,
chess, and tic-tac-toe. For the system administrator,
there were tools to dump and restore disk images to
magnetic tape, to read and write paper tapes, and to
create, check, mount, and unmount removable disk packs.

Most important, the system offered an interactive
environment that by this time allowed time-sharing, so
several people could use a single machine at once.
Various programming languages were available to them,
including BASIC, Fortran, the scripting of Unix
commands, assembly language, and B. The last of these, a
descendant of a BCPL (Basic Combined Programming
Language), ultimately evolved into the immensely popular
C language, which Ritchie created while also working on

The first edition of Unix let programmers call 34
different low-level routines built into the operating
system. It's a testament to the system's enduring nature
that nearly all of these system calls are still
available-and still heavily used-on modern Unix and
Linux systems four decades on. For its time, first--
edition Unix provided a remarkably powerful environment
for software development. Yet it contained just 4200
lines of code at its heart and occupied a measly 16 KB
of main memory when it ran.

Unix's great influence can be traced in part to its
elegant design, simplicity, portability, and
serendipitous timing. But perhaps even more important
was the devoted user community that soon grew up around
it. And that came about only by an accident of its
unique history.

The story goes like this: For years Unix remained
nothing more than a Bell Labs research project, but by
1973 its authors felt the system was mature enough for
them to present a paper on its design and implementation
at a symposium of the Association for Computing
Machinery. That paper was published in 1974 in the
Communications of the ACM. Its appearance brought a
flurry of requests for copies of the software.

This put AT&T in a bind. In 1956, AT&T had agreed to a
U.S government consent decree that prevented the company
from selling products not directly related to telephones
and telecommunications, in return for its legal monopoly
status in running the country's long-distance phone
service. So Unix could not be sold as a product.
Instead, AT&T released the Unix source code under
license to anyone who asked, charging only a nominal
fee. The critical wrinkle here was that the consent
decree prevented AT&T from supporting Unix. Indeed, for
many years Bell Labs researchers proudly displayed their
Unix policy at conferences with a slide that read, "No
advertising, no support, no bug fixes, payment in

With no other channels of support available to them,
early Unix adopters banded together for mutual
assistance, forming a loose network of user groups all
over the world. They had the source code, which helped.
And they didn't view Unix as a standard software
product, because nobody seemed to be looking after it.
So these early Unix users themselves set about fixing
bugs, writing new tools, and generally improving the
system as they saw fit.

The Usenix user group acted as a clearinghouse for the
exchange of Unix software in the United States. People
could send in magnetic tapes with new software or fixes
to the system and get back tapes with the software and
fixes that Usenix had received from others. In
Australia, the University of New South Wales and the
University of Sydney produced a more robust version of
Unix, the Australian Unix Share Accounting Method, which
could cope with larger numbers of concurrent users and
offered better performance.

By the mid-1970s, the environment of sharing that had
sprung up around Unix resembled the open-source movement
so prevalent today. Users far and wide were
enthusiastically enhancing the system, and many of their
improvements were being fed back to Bell Labs for
incorporation in future releases. But as Unix became
more popular, AT&T's lawyers began looking harder at
what various licensees were doing with their systems.

One person who caught their eye was John Lions, a
computer scientist then teaching at the University of
New South Wales, in Australia. In 1977, he published
what was probably the most famous computing book of the
time, A Commentary on the Unix Operating System, which
contained an annotated listing of the central source
code for Unix.

Unix's licensing conditions allowed for the exchange of
source code, and initially, Lions's book was sold to
licensees. But by 1979, AT&T's lawyers had clamped down
on the book's distribution and use in academic classes.
The anti-authoritarian Unix community reacted as you
might expect, and samizdat copies of the book spread
like wildfire. Many of us have nearly unreadable nth--
generation photocopies of the original book.

End runs around AT&T's lawyers indeed became the norm-
even at Bell Labs. For example, between the release of
the sixth edition of Unix in 1975 and the seventh
edition in 1979, Thompson collected dozens of important
bug fixes to the system, coming both from within and
outside of Bell Labs. He wanted these to filter out to
the existing Unix user base, but the company's lawyers
felt that this would constitute a form of support and
balked at their release. Nevertheless, those bug fixes
soon became widely distributed through unofficial
channels. For instance, Lou Katz, the founding president
of Usenix, received a phone call one day telling him
that if he went down to a certain spot on Mountain
Avenue (where Bell Labs was located) at 2 p.m., he would
find something of interest. Sure enough, Katz found a
magnetic tape with the bug fixes, which were rapidly in
the hands of countless users.

By the end of the 1970s, Unix, which had started a
decade earlier as a reaction against the loss of a
comfortable programming environment, was growing like a
weed throughout academia and the IT industry. Unix would
flower in the early 1980s before reaching the height of
its popularity in the early 1990s.

For many reasons, Unix has since given way to other
commercial and noncommercial systems. But its legacy,
that of an elegant, well-designed, comfortable
environment for software development, lives on. In
recognition of their accomplishment, Thompson and
Ritchie were given the Japan Prize earlier this year,
adding to a collection of honors that includes the
United States' National Medal of Technology and
Innovation and the Association of Computing Machinery's
Turing Award. Many other, often very personal, tributes
to Ritchie and his enormous influence on computing were
widely shared after his death this past October.

Unix is indeed one of the most influential operating
systems ever invented. Its direct descendants now number
in the hundreds. On one side of the family tree are
various versions of Unix proper, which began to be
commercialized in the 1980s after the Bell System
monopoly was broken up, freeing AT&T from the
stipulations of the 1956 consent decree. On the other
side are various Unix-like operating systems derived
from the version of Unix developed at the University of
California, Berkeley, including the one Apple uses today
on its computers, OS X. I say "Unix-like" because the
developers of the Berkeley Software Distribution (BSD)
Unix on which these systems were based worked hard to
remove all the original AT&T code so that their software
and its descendants would be freely distributable.

The effectiveness of those efforts were, however, called
into question when the AT&T subsidiary Unix System
Laboratories filed suit against Berkeley Software Design
and the Regents of the University of California in 1992
over intellectual property rights to this software. The
university in turn filed a counterclaim against AT&T for
breaches to the license it provided AT&T for the use of
code developed at Berkeley. The ensuing legal quagmire
slowed the development of free Unix-like clones,
including 386BSD, which was designed for the Intel 386
chip, the CPU then found in many IBM PCs.

Had this operating system been available at the time,
Linus Torvalds says he probably wouldn't have created
Linux, an open-source Unix-like operating system he
developed from scratch for PCs in the early 1990s. Linux
has carried the Unix baton forward into the 21st
century, powering a wide range of digital gadgets
including wireless routers, televisions, desktop PCs,
and Android smartphones. It even runs some

Although AT&T quickly settled its legal disputes with
Berkeley Software Design and the University of
California, legal wrangling over intellectual property
claims to various parts of Unix and Linux have continued
over the years, often involving byzantine corporate
relations. By 2004, no fewer than five major lawsuits
had been filed. Just this past August, a software
company called the TSG Group (formerly known as the SCO
Group), lost a bid in court to claim ownership of Unix
copyrights that Novell had acquired when it purchased
the Unix System Laboratories from AT&T in 1993.

As a programmer and Unix historian, I can't help but
find all this legal sparring a bit sad. From the very
start, the authors and users of Unix worked as best they
could to build and share, even if that meant defying
authority. That outpouring of selflessness stands in
sharp contrast to the greed that has driven subsequent
legal battles over the ownership of Unix.

The world of computer hardware and software moves
forward startlingly fast. For IT professionals, the
rapid pace of change is typically a wonderful thing. But
it makes us susceptible to the loss of our own history,
including important lessons from the past. To address
this issue in a small way, in 1995 I started a mailing
list of old-time Unix -aficionados. That effort morphed
into the Unix Heritage Society. Our goal is not only to
save the history of Unix but also to collect and curate
these old systems and, where possible, bring them back
to life. With help from many talented members of this
society, I was able to restore much of the old Unix
software to working order, including Ritchie's first C
compiler from 1972 and the first Unix system to be
written in C, dating from 1973.

One holy grail that eluded us for a long time was the
first edition of Unix in any form, electronic or
otherwise. Then, in 2006, Al Kossow from the Computer
History Museum, in Mountain View, Calif., unearthed a
printed study of Unix dated 1972, which not only covered
the internal workings of Unix but also included a
complete assembly listing of the kernel, the main
component of this operating system. This was an amazing
find-like discovering an old Ford Model T collecting
dust in a corner of a barn. But we didn't just want to
admire the chrome work from afar. We wanted to see the
thing run again.

In 2008, Tim Newsham, an independent programmer in
Hawaii, and I assembled a team of like-minded Unix
enthusiasts and set out to bring this ancient system
back from the dead. The work was technically arduous and
often frustrating, but in the end, we had a copy of the
first edition of Unix running on an emulated PDP-11/20.
We sent out messages announcing our success to all those
we thought would be interested. Thompson, always
succinct, simply replied, "Amazing." Indeed, his
brainchild was amazing, and I've been happy to do what I
can to make it, and the story behind it, better known.
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PostPosted: Thu 19 Jan 2012, 12:15    Post subject:  

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