The UNIX Operating System
The UNIX* (link to UNIX - Trademark file) operating
system was designed to let a number
of programmers access the computer at the same time and share its resources.
The operating system coordinated the use of the computer's resources,
allowing one person, for example, to run a spell check program while another
creates a document, while another edits a document and another creates
graphics, while still another formats a document -- all at the same time,
with each user oblivious to the activities of the other users.
The operating system controls all of the commands from all of the keyboards
and all of the data being generated, and permits each user to believe he
or she was the only person working on the computer.
This real-time sharing of resources make UNIX the most powerful operating
system of its day, and to many even to this day.
Although UNIX was developed by programmers for programmers, it provides
an environment so powerful and flexible that it soon found applications
in business, science, and industry. Many telecommunications switches and
transmission systems are controlled by administration and maintenance systems
based on UNIX.
While initially designed for medium-sized minicomputers, the operating
system was soon moved to larger, more popwerful mainframe computers. As
personl computers grew in popularity, versions of UNIX found their way
into these boxes, and a number of companies produce UNIX-based machines
for the scientific and programming communities.
The uniqueness of UNIX
There are a number of features that made UNIX a hit from the start:
-
Multitasking capability
-
Multiuser capability
-
Portability
-
Many UNIX programs
-
Library of application software
Multitasking
Many computers do one thing at a time, just as we do one thing at a time.Oh,
we may be able to talk and drive a car at the same time, but let's face
it, when we're doing one thing we may not be paying complete attention
to the other task.
UNIX lets a computer do several things at once, such as printing out
one file while the user edits another file. This is a major feature for
users, since they don't have to wait for one application to end before
starting another one.
Multiusers
The same design that permits multitasking permits multiple users to use
the computer. The computer can take the commands of a number of users --
determined by the design of the computer -- to run programs, access files,
and print documents at the same time.
The computer can't tell the printer to print all the requests at once,
but it does prioritize the requests to keep everything orderly. It also
lets several users access the same dpocument by compartmentalizing the
document so that the changes of one user don't override the changes of
another user.
System portability
A major contribution of the UNIX system was its portability, permitting
it to move from one brand of computer to another with a minimum of code
changes. At a time when different computer lines of the same vendor didn't
talk to each other, that meant a great savings in both hardware and software
upgrades.
It also meant that the operating system could be upgraded without having
all the customer's data inputted again. And new versions of UNIX were backward
compatible with older versions, making it easier for companies to upgrade
in an orderly manner.
UNIX tools
UNIX comes more than ???400??? programs that
can divided into two classes:
-
Integral utilities that are absolutely necessary for the operation
of the computer, such as the command interpreter, and
-
Tools that aren't necessary for the operation of UNIX but provide
the user with additional capabilities, such as typesettin capabilities
and e-mail.
(Illustration of multi-cubes that make up a UNIX
system. See Thomas and Yates, p. 5)
Caption: Tools can
be added or removed from a UNIX system, depending upon the applications
required.
UNIX Communications
E-mail is commonplace today, but it has only come into its own in the bsuiness
community within the last 10 years. Not so with UNIX users, who have been
e-mailing each other for several decades.
UNIX e-mail at first permitted users on the same computer to communicate
with each other via their terminals. Then users on different machines,
even made by different vendors, were connected.to support e-mail.. And
finally, UNIX systems around the world were linked into a world wide web
two decades before the development of today's World Wide Web.
Applications librarys
UNIX as it is known today didn't just develop overnight. Nor were just
a few people responsible for it's growth. As soon as it moved from Bell
Labs into the universities, every computer programmer worth his or her
own salt started developing programs for UNIX.
Today there are more than ???500??? UNIX
applications that can be purchased from third-party vendors, in addition
to the applications that come with UNIX.
How UNIX is organized
The UNIX system if functionally organized at three levels:
-
The kernel, which schedules tasks and manages storage;
-
The shell, which connects and interprets users' commands, calls programs
from memory, and executes them; and
-
The tools and applications that offer additional functionality to the operating
system
(Illustration of tools and applications, shell and
kernel (Thomas and Yates, p. 11)
Caption: The three levels of the UNIX system,
kernel, shell, and tools and applications.
The kernel
The heart of the operating syste, the kernel controls the hardware and
turns part of the system on and off at the programmers's command. If you
ask the computer to list (ls) all the files in a directory, the kernal
tells the computer to read all the files in that directory from the disk
and display them on your screen.
The shell
There are several types of Shell, most notably the command-driven Bourne
Shell and the C Shell (no pun intended), and menu-driven shells that make
it easier for beginners to use. Whatever shell is used, its purpose remains
the same -- to act as an interpreter between the user an the computer.
The shell also provides the functionality of "pipes," whereby a number
of commands can be linked together by a user, permitting the output of
one program to become the input to another program.
Tools and applications
There are more than ??? tools that are available
to UNIX users, although some may be written by third-party vendors for
specific applications. Typically, tools are generally grouped into categories
for certain fucntions, such as word processing, business pplications, or
programming.
The many faces of UNIX
Bell Labs contunually improved UNIX, and issued new versions with additional
features for both programmers and businesses. Today there are X???
versions
of UNIX, (link to Chart in UNIX - Main file)
plus a variety of implementations, customized versions for specific applications
or computers.
One of the most popular implementations today is LINUX, which is used
(???where and by who???).
Other implementations include Microsoft's XENIX, 3BSD and NetBSD. (???need
to explain who owns???)
Who uses UNIX today?
Unlike personal computers (PCs), a typlcal UNIX system
is physically large since it must support many users and offers a large
set of programs. Generally a system administrator is required to run the
system, so it generally is found in large organizations. The system is
ideal for companies who have large electronic communications applications,
and UNIX-based computers are less expensive than mii- and mainframe computers.
UNIX users often share common files of information,
use large data bases together, and keep their files in one large file system
accesible to multiple users.
Walk into any research facility, university, or
programming environment, and you will find UNIX at work. And UNIX can be
found in the buiness environment, where it excells in text preparation,
electronic mail, and database management..
Andl although invisible to end users, UNIX is
the backbone of many telecommunications mintenance, operating, and administration
systems, helping monitor electronic switches and fiber optic transmission
systems, and even billing customers for their telephone and data transmission
usage.
It is the invisible operating system for millions
of people who rely on it, but who aren't really aware that it is there.
References
Consult any bookstore or library for the many books
written about UNIX. Seminal technical papers on UNIX can be found at
(link to the references in Ritchie's 1984 paper at http://cm.bell-labs.com/cm/cs/who/dmr/hist.html#pipes
???)
Additional information can be found at
(link to UNIX - For more info file)
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