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Unix Operating SystemUnix Operating System
Mark Shacklette,The University of ChicagoIntroduction 494
History 494
Early History (1969–1972) 494
Infancy and Politics 496
The Great Schism 497
BABEL: The Commercialization of Unix 498
How to Recognize a Unix System When You
See One 499
What Is a Unix System? 499
Files and Directories 499
System Users 499
Login Processing 500
The Home Directory 500
Online Help System 500
Pipes and Filters 500
Core Components 501
Editors 501
Command Interface: The Shell 501Summary of Popular Commands 506
Operating System Structure 506
Kernel Structure 506
Filesystem 507
Security 508
The Unix Philosophy 508
Write Small Programs That Do One
Thing Well 508
Write Programs to Communicate Over
a Common Data Format 508
Everything Is a File 509
Central Priorities 509
Conclusion 510
Glossary 510
Cross References 511
References 511
Further Reading 511INTRODUCTION
Unix is a powerful operating system that began life in the
late 1960s and has continued to exert a powerful influence
on operating systems to this day. The Unix operating sys-
tem is known as amultiuser, multitaskingoperating sys-
tem. This means that more than one user can be logged
into and execute multiple programs on the system at the
same time. Most people intuitively believe that personal
computers were first introduced by IBM in the late 1970s
with the delivery of the IBM Personal Computer. In re-
ality, computers were, for the most part, personal com-
puters from the very beginning, in the sense that most
computers only allowed one user to work on the com-
puter at a given time. In addition, that single user would
only be able to run a single program at a given time. This
notion of one user running one program after another
is a concept known asbatch sequential processing.Pro-
grams that individual users would want to run would be
scheduled as a “batch.” The various programs in abatch
would be run one after the other, until the batch was
completed.
Before Unix, programs would be entered on punch
cards, or “IBM cards,” and these cards would be placed
into a machine called a card reader. The system would
then execute the program. Output from these programs,
known as “jobs,” would be in the form of paper printouts
from a printer. A programmer would know the results of
her program only when the job was completed and output
had been produced from the printer. If a mistake (often
called a “bug”) was discovered, the bug would have to be
resolved, new cards created, and the entire process exe-
cuted again—a time-consuming, tedious, and laborious
process by any standard.Unix is an operating system written by programmers
for programmers. Programmers were tired of having to
work with punch cards, and having to wait, sometimes
for hours or even days, for the results of their program. It
was a waste of valuable time. How much nicer it would be
to be able to enter programs directly into the computer by
typing at a terminal and submitting the program directly
to the operating system to run—to run immediately and to
allow multiple programmers to do this at the same time.
Enter Unix.HISTORY
Early History (1969–1972)
The history of the Unix operating system is itself a story
full of intrigue, lawsuits, corporate and federal politics,
budgetary concerns, computer games, antitrust law, law-
suits, resourcefulness, and, when the going got rough,
subterfuge. It is a story about a few very smart people
armed with a few very good ideas. The story reads at times
like any great spy novel, full of plots and subplots, intrigu-
ing personalities, battles for territory, winners and losers.
It even has a chapter on the illegal and surreptitious un-
derground transmission of contraband books. It is a story
whose participants seem compelled, like some ancient
bearded mariner, to tell and retell, if for no other reason
than to remind ourselves and the world that good ideas are
always possible, always to be valued, and sometimes, just
sometimes, may win through pure unabashed brilliance.
In the end, the story of Unix is an unlikely story, a story
that at any of a number of points in its development might
not have happened at all, were it not for the commingling
of those few very good ideas in the minds of those few
smart people. That, of course, and the subterfuge.494