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<A HREF="#I1">45 — UNIX Flavors</A></LI>
<UL>
<UL>
<UL>
<LI>
<A HREF="#I3">By S. Lee Henry</A></LI></UL></UL>
<LI>
<A HREF="#I4">The Beginnings of UNIX</A></LI>
<LI>
<A HREF="#I5">From Lab to Mainstream</A></LI>
<LI>
<A HREF="#I6">Factors Leading to UNIX's Early Success</A></LI>
<UL>
<LI>
<A HREF="#I7">The UNIX Model of Computing</A></LI>
<LI>
<A HREF="#I8">Portability</A></LI>
<LI>
<A HREF="#I9">Extensibility</A></LI>
<LI>
<A HREF="#I10">Additional Features</A></LI>
<LI>
<A HREF="#I11">Appeal</A></LI></UL>
<LI>
<A HREF="#I12">Flavors BSD and System V</A></LI>
<LI>
<A HREF="#I13">Open Systems</A></LI>
<LI>
<A HREF="#I14">The Role of Standards and Consortiums</A></LI>
<UL>
<LI>
<A HREF="#I15">SVID</A></LI>
<LI>
<A HREF="#I16">POSIX</A></LI>
<LI>
<A HREF="#I17">X/Open</A></LI>
<LI>
<A HREF="#I18">COSE/CDE</A></LI></UL>
<LI>
<A HREF="#I19">War and Peace</A></LI>
<LI>
<A HREF="#I20">The UNIX Future</A></LI></UL></UL></UL>
<H2 ALIGN="CENTER">
<CENTER><A ID="I1" NAME="I1">
<FONT SIZE=5><A ID="I2" NAME="I2"></A><B>45 — UNIX Flavors</B>
<BR></FONT></A></CENTER></H2>
<H5 ALIGN="CENTER">
<CENTER><A ID="I3" NAME="I3">
<FONT SIZE=3><B>By S. Lee Henry</B>
<BR></FONT></A></CENTER></H5>
<P>The UNIX operating system has clearly emerged as one of the primary software platforms for the '90s, providing distributed computing capabilities for even the most diverse networks. Its remarkable success has been due both to its portability and to its
long history of innovation. In the more than 25 years that UNIX has been around, it has had plenty of time to "soak up" good ideas from some of the sharpest computer people in the business. From AT&T, the University of California at Berkeley,
Sun Microsystems, and many other companies, UNIX has acquired a tremendous collection of powerful tools and maintained an open architecture that continues to invite development.
<BR></P>
<P>UNIX today runs on three or four million computers, maybe more. These computers range from very small personal computers to Crays. The concept of creating ad hoc "programs" by interconnecting commands is extremely powerful whether you're
working on a laptop or a supercomputer.
<BR></P>
<P>Because of its portability and because of an elegant design that appeals to developers, UNIX has proliferated into many different "flavors" over the past couple decades. As much as this divergence has profited UNIX by providing many venues for
innovation, it has also frustrated the growing need for portable applications. Without an adequate market share, any particular UNIX flavor has suffered from a dearth of software or, at least, a dearth of affordable software, especially compared with
personal computer systems such as those built by IBM and Apple. The flavors of UNIX are different enough that it became difficult and, therefore, costly to port applications from one to the other. In addition, UNIX is not the same simple creature that it
was back in Bell Labs. Windowing systems, graphical user interfaces, and years of innovation have complicated UNIX and dramatically affected the complexity of porting applications.
<BR></P>
<P>The need for simplified application portability was not, however, the only factor pushing for a more unified UNIX. Improvements in networking put interoperability among different UNIX systems, as well as between UNIX and non-UNIX systems, high on
everyone's agenda. Today's businesses are demanding enterprise-wide computing solutions. These solutions entail a high degree of data sharing—both distributed applications and an ease of moving information and people expertise around the organization.
Today's procurements are specifying standard interfaces and protocols to help meet this demand and leverage organizations' investments in computing technology.
<BR></P>
<P>As a result, the UNIX command sets and the programming interfaces are becoming increasingly standardized and a number of startling alliances between UNIX competitors are bringing a new unity to UNIX.
<BR></P>
<P>This chapter briefly reviews the history of UNIX, describes some of the main "flavors" of UNIX that are popular today, addresses the most important standards that are helping to bring unity to UNIX, and predicts what will happen to UNIX in the
remainder of the '90s.
<BR></P>
<H3 ALIGN="CENTER">
<CENTER><A ID="I4" NAME="I4">
<FONT SIZE=4><B>The Beginnings of UNIX</B>
<BR></FONT></A></CENTER></H3>
<P>If you feel that you've cut your teeth on UNIX, its early history at Bell Labs may seem extremely remote. UNIX was created at AT&T's Bell Labs roughly 25 years ago, where technological innovation and engineering elegance seemed to reign over more
worldly concerns such as proprietorship.
<BR></P>
<P>In those days, operating systems were difficult to use and programmers had to work hard to make their programs acceptable to the difficult-to-please computers. The convenient shell environments that you use today did not, for the most part, exist.
<BR></P>
<P>UNIX, first called UNICS, was built to run on the DEC PDP-7 and PDP-11 systems. It was not intended to be a product. Its designers, Ken Thompson and Dennis Ritchie, were after usability and had no thoughts about marketing it. They were simply looking to
create a more hospitable programming environment, so they created and enhanced UNIX basically for their own use. In time, other people at Bell Labs contributed additional concepts and tools and, by 1969, the basics of UNIX were established.
<BR></P>
<P>Given this beginning, it is extremely ironic that UNIX has become not only one of the most successful operating systems ever but that it has influenced every other important operating system as well. For an operating system first developed by experts
for experts, the impact that UNIX has had on the industry has been nothing short of staggering. UNIX has had a transforming influence on all computer operating systems since its first introduction into popular use. Even single-user operating systems such
as DOS (in releases after 2.0) have taken on many of the characteristics and capabilities of UNIX. The hierarchical file system, which allows a much better way of organizing files than the previous "flat" file space, for example, is incorporated
into DOS (except that it does not have a root directory). Search paths and pipes have also worked their way into DOS as has the more command for viewing subsequent pieces of a file.
<BR></P>
<P>The more modern Windows NT incorporates many characteristics of UNIX from the basic file metaphor (that is, virtually everything is a file) and hierarchical file system to support for named pipes for interprocess communication and the use of STREAMS in
networking. Windows NT has also implemented many of the most important features of UNIX, including multitasking, multiprocessing, and security. Although UNIX has had enhancing effects on many other operating systems, its capabilities still continue to set
it in a class by itself. Among these capabilities, its availability over a variety of hardware platforms, its multiuser character, and its support of parallel processing and distributed file systems make it ideal for large heterogeneous networks.
<BR></P>
<H3 ALIGN="CENTER">
<CENTER><A ID="I5" NAME="I5">
<FONT SIZE=4><B>From Lab to Mainstream</B>
<BR></FONT></A></CENTER></H3>
<P>The small group of people who created UNIX consisted of AT&T members of a development team looking at an operating system called MULTICS. MULTICS was a time-sharing and multitasking operating system developed at MIT in the '60s. It ran on computers
built by General Electric. MULTICS had many important features, but it was complex and unwieldy. When AT&T eventually withdrew its participants, they were left without an operating system but with plenty of good ideas about what a modern time-sharing
system should be like. In fact, despite the early disappearance of MULTICS, the astounding success of UNIX owes a considerable amount to several ideas of this then-aggressive operating system. MULTICS had the concept of the shell as command interpreter and
a hierarchically arranged file system. Both of these features became features of the new UNIX system as well. Just as important, MULTICS was also one of the first operating systems to support more than one user at a time. This one feature made UNIX
especially valuable in its early customer environments, most notably academic and research establishments, where the need to share computer systems was extremely important.
<BR></P>
<P>When AT&T decided to license UNIX on DEC minicomputers to educational institutions in 1974, it gave no-cost licenses and source code. Unlike companies such as Microsoft that maintain tight control over source code, AT&T practically gave UNIX
away, complete with source code, for the asking. This early availability of UNIX source code to universities meant that hundreds of thousands of bright computer scientists and engineers who could use UNIX, support UNIX, and modify UNIX began flooding the
market a few years later. Their expertise led to the early success of UNIX and to much of the divergence of UNIX into many custom versions. The further development of UNIX both within the universities and within the organizations that these UNIX experts
began working for quickly began moving UNIX in many new directions at once.
<BR></P>
<P>By 1977, UNIX was ready for more commercial use. Digital Equipment was, at the time, emphasizing smaller systems with fewer users. The minicomputer era was getting off the ground, and UNIX had an ideal platform in the PDP series systems because even
universities could afford to own them.
<BR></P>
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