MirOS Manual: jus(PAPERS)

        Berkeley UNIX Yesterday, Today and Tomorrow

                        Keith Bostic

                   Marshall Kirk McKusick

                     Michael J. Karels

              Computer Systems Research Group
                 Computer Science Division
 Department of Electrical Engineering and Computer Science
             University of California, Berkeley
                Berkeley, California  94720


          This paper presents a brief overview  of  the
     historic  Berkeley  releases  and  the  role  that
     Berkeley  has  played  in  the  UNIX-  world   and
     discusses  the  role  that University and research
     releases should play in the future.

1. A Technical History of the Berkeley Project

     This is a brief technical history of Berkeley UNIX. For
more  details,  [McKusick85]  is  strongly recommended along
with the other  papers  listed  in  the  Reference  section.
Specifically,  we  apologize that space does not permit men-
tioning most of the major contributors and influences on the
Berkeley system!

     The University of California, Berkeley, first ran  Bell
Laboratories  Version  4  UNIX on a PDP-11/45, in January of
1974. Later that spring, a PDP-11/40 was configured with the
newly  available  Version 5. Version 6 was running on a PDP-
11/70 by the fall of 1975, with the arrival of two new  gra-
duate  students,  Bill  Joy  and Chuck Haley. They initially
concentrating on making  improvements  to  a  Pascal  system
written  by  Ken  Thompson  while on sabbatical at Berkeley.
With this completed, they turned their attention to  the  ed
editor,  eventually  producing a new version they called ex.
By the end of the summer of 1976, Joy  and  Haley  began  to
take  an  interest  in  exploring  the internals of the UNIX
-UNIX is a registered trademark of UNIX System  Labora-

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     In 1977, a steady stream of requests for  the  enhanced
Pascal  system  had begun. Early that year, Joy put together
the first ``Berkeley Software Distribution'', including  the
Pascal  system  and  the  source  to ex. Over the next year,
about thirty copies of this distribution were sent  out.  At
around  the  same time, Joy began work on what was to become
vi. By mid-1978, the software distribution clearly needed to
be  updated.  The  Pascal system had been made markedly more
robust through feedback from its expanding  user  community,
and  had  been split into two passes so that it could be run
on PDP-11/34s. The result of the  update  was  the  ``Second
Berkeley  Software  Distribution''  a  name that was quickly
abbreviated to 2BSD. Along with the Pascal  system,  vi  and
termcap for several terminals were included. Once again Bill
Joy single-handedly put together distributions, answered the
phone,  and incorporated user feedback into the system. Over
the  next  year  nearly  seventy-five  tapes  were  shipped.
Although  Joy soon moved on to other projects, the 2BSD dis-
tribution continued to expand. Today the latest  version  of
this  distribution, 2.10BSD is still alive and being used by
people all around the world on PDP-11's.

     Early in 1978,  Berkeley  obtained  a  newly  announced
Digital Equipment Corp. (DEC) VAX= 11-780's.  Shortly  after
the  arrival of the VAX, Bell Laboratories provided Berkeley
with a copy of their 32/V port of UNIX to the VAX.  Although
32/V  supported  a Version 7 UNIX environment on the VAX, it
did not take advantage of the virtual memory  capability  of
the  VAX  hardware.  Like its predecessors on the PDP-11, it
was a swapping system. Ozalp Babaoglu, a  Berkeley  graduate
student,  set  about finding a way of implementing a working
set paging system on the VAX. As Babaoglu neared the comple-
tion   of   his  first  attempt  at  an  implementation,  he
approached Bill Joy  for  some  help  in  understanding  the
intricacies  of  the  UNIX  kernel.  Intrigued by Babaoglu's
approach, Joy joined in helping to integrate the  code  into
32/V and then with the ensuing debugging.

     Joy realized that the 32-bit VAX would  soon  make  the
16-bit  PDP-11  obsolete,  and  he  began  to  port the 2BSD
software to the VAX. By the end of 1979, a complete  distri-
bution had been created. This distribution included the vir-
tual memory kernel, the standard  32/V  utilities,  and  the
2BSD  additions,  which  by  now included the Pascal system,
ex/vi, the Cshell and several other utilities. In  December,
1979,  Joy  shipped  the first of nearly a hundred copies of
3BSD, the first VAX distribution from Berkeley.

=VAX is a registered  trademark  of  Digital  Equipment

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     In the fall of 1979, the Defense Advanced Research Pro-
jects Agency, DARPA, accepted a Berkeley proposal to develop
an enhanced version of 3BSD for the  DARPA  community.  With
the already good reputation of 3BSD supporting the proposal,
the Berkeley project was funded. Joy took charge of the pro-
ject,  which  was  to  become  the Computer Systems Research
Group (CSRG). Joy soon incorporated job control, added  auto
reboot,  a  1K block file system, and support for the latest
VAX machine, the VAX-11/750. By October,  1980,  a  polished
distribution that also included the Franz Lisp system and an
enhanced mail handling system was released as  4BSD.  During
its nine-month lifetime, nearly 150 copies were shipped.

     With the increasingly wide distribution and  visibility
of Berkeley UNIX, several critics began to emerge. The major
objection cited was the performance of various benchmarks as
compared  to  the DEC VMS system. Over the course of several
months, Joy systematically tuned the kernel,  soon  matching
VMS's  performance.  Rather than continue shipping 4BSD, the
tuned system, with the addition of Robert Elz's auto  confi-
guration  code,  was  released as 4.1BSD in June, 1981. Over
its two year lifetime about 400 distributions were shipped.

     With the release of 4.1BSD, much  of  the  debate  over
performance  died  down.  DARPA  again funded Berkeley, this
time with the intention of adding new features  to  the  BSD
system.  These  new  features  eventually  included Berkeley
reliable signals, the fast filesystem, disk quotas, and  the
socket interface with TCP/IP networking support. Around this
time Joy left the CSRG for Sun Microsystems, and Sam Leffler
took  over  responsibility  for  completing  the project. In
August, 1983, this system was released  as  4.2BSD  [Joy83].
The  popularity  of  4.2BSD  was impressive; within eighteen
months more copies of 4.2BSD had been shipped  than  of  all
the previous Berkeley software distributions combined.

     As with 4BSD, the major criticism of 4.2BSD was perfor-
mance.  The  problem,  not  surprisingly,  was  that the new
facilities had not been tuned and that many  of  the  kernel
data  structures  were not well suited to their new uses. In
addition, many of the interfaces, particularly in  the  net-
working  area  had  been left unfinished. As Sam Leffler had
left the CSRG for Lucasfilm, the tuning and  enhancement  of
4.2BSD  was  largely  done  under  the  direction of Michael
Karels and Kirk McKusick [Leffler84] [McKusick85]. This sys-
tem was released in April of 1986 as 4.3BSD, and had greatly
enhanced performance and reliability over 4.2BSD, along with
several new features.

     As it had done in 4.2BSD, the CSRG then embarked  on  a
new  development  phase  to update other major components of
the system, and design and integrate new functionality.  The
4.4BSD release, scheduled for fall of 1992, will contain the
results of several major new projects. Among these  projects

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are  an  OSI network protocol suite integrated with existing
ISO applications, an IEEE POSIX 1003.1 standard interface, a
highly  tuned  TCP/IP  networking interface, support for Sun
Microsystem's Network File  System,  the  integration  of  a
log-structured  file system, an integration of the MACH vir-
tual memory system, volume labels  and  user-level  database

     There will have been four interim releases made by  the
CSRG  between  4.3BSD  and  the upcoming 4.4BSD release. The
first two of these releases,  4.3BSD-Tahoe  and  4.3BSD-Reno
were  intended to distribute a subset of the new functional-
ity found in 4.4BSD available to vendors.  The  4.3BSD-Tahoe
release,  made in the summer of 1988, was the first Berkeley
release to support two architectures.  This  goal  was  made
possible  by  the  reimplementation  of  much of the machine
specific kernel source and a  fundamental  restructuring  of
the  source  code  pool  so  that binaries for more than one
architecture could be constructed from a single source pool.
The  two  supported  architectures were the VAX and the Com-
puter Consoles Inc.  Power  6/32  (the  Tahoe).  Since  this
release, architecture support for the Intel 386/486, the Sun
Microsystems SPARCstation- I and II, the DECstation 3100 and
5000  and  the  Hewlett-Packard 300 have been added as well.
The 4.3BSD-Reno release, made in the  summer  of  1990,  was
intended  to  make the Network File System code available to
vendors using Berkeley-derived systems,  such  as  The  Open
Software  Foundation  (OSF).  This  code had been written by
Rick Macklem at the University of Guelph and  integrated  by
the  CSRG,  under  a  new  version of the kernel file system

     Two  other  interim  releases,  the  first  and  second
release  of  the ``Berkeley Network Software Distribution'',
usually abbreviated as NET/1 and  NET/2,  were  intended  to
make  the  source  code  of the 4BSD system available to and
redistributable by anyone. Over the years of development  by
the  CSRG  and  others, an increasingly larger percentage of
the system was not derived from the original AT&T 32/V  dis-
tribution.  In  the  spring  of 1988 Berkeley made its first
distribution not requiring an AT&T  source  license,  NET/1.
This  distribution  primarily  contained the networking por-
tions of the system, from the utilities all the way  through
to  the  kernel device drivers, although other items such as
login and other files were  included  for  various  reasons.
This  release  was  extremely popular with many vendors with
their own versions of UNIX but who wished to run the  Berke-
ley  TCP/IP  code  and  with vendors wishing to create smart
networking cards, not  to  mention  the  users  that  wanted
-All SPARC  trademarks  are  trademarks  or  registered
trademarks of SPARC International, Inc. SPARCstation is
licensed exclusively to Sun Microsystems, Inc.

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access to the source code for class work or  other  research

     Around this time, the CSRG also  began  to  search  out
freely redistributable versions of the UNIX utilities and to
rewrite, or encourage BSD users to rewrite, those that  were
not   available  elsewhere.  This  was  an  immensely  time-
consuming task, involving contributions by hundreds of  pro-
grammers  from  all around the world. In the summer of 1991,
Berkeley released NET/2, which, like NET/1, did not  require
an AT&T source license. The NET/2 release included about 80%
of the source code found in the  4.3BSD-Reno  release.  This
release has proved to be immensely popular, with hundreds of
thousands of copies taken from the public  network  archives
and an unknown number redistributed by other organizations.

2. The Role of the Berkeley Project in the UNIX World

     The role that Berkeley has played in the UNIX world has
been  a constantly changing one. In the 1970's, Berkeley was
among the first participants in the UNIX research community,
acting  as  host  to  several researchers on sabbatical from
Bell Laboratories. This  cooperation  typified  the  harmony
that  was characteristic of the early UNIX community, as led
by Bell Laboratories.  Work  that  was  contributed  to  the
Laboratories by different members of the community, Berkeley
among them, helped produce a rapidly expanding set of  tools
and facilities. With the commercialization of UNIX, the Bell
Laboratories researchers were no longer able  to  act  as  a
clearinghouse for the ongoing UNIX research. As the research
community continued to modify the UNIX system, it found that
it  needed  an  organization that could produce leading edge
research releases. Because of its early involvement in  UNIX
and  its  history  of  releasing  UNIX-based tools, the CSRG
quickly filled this role.

     For the first half of the 1980's,  Berkeley  served  as
the focus of the leading edge of UNIX research. The Berkeley
system was widely used, ported and considered the arbiter of
what  should  comprise  a  UNIX  system.  By the mid-1980's,
largely because the networking  component  of  the  Berkeley
system  was unique and unavailable from vendors for a period
of time, Berkeley was forced  into  the  role  of  a  vendor
[McKusick89].  This  role  expanded  to the point that there
were two major variants of  UNIX,  System  V  and  BSD,  and
resulted  in  a breach in the UNIX world that is only gradu-
ally being healed. Acting as a vendor  required  an  immense
amount  of  time, money and effort by the CSRG. Thousands of
hours were devoted to release engineering, thousands more to
participation  in  the emerging UNIX standards and thousands
more in distribution and user support.  Over  the  years  it
became  increasingly clear to the people associated with the
Berkeley UNIX project that its limited funding and  manpower
were   insufficient  to  complete  its  historical  task  of

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designing, implementing and supporting a complete, reliable,
leading  edge  system.  As each portion of the system became
more complex and additional features were  added,  more  and
more  effort had to be expended to keep the system at a high
level of quality, and less and less effort was available  to
move the system technically forward. Fortunately, during the
last half of the 1980's, as the UNIX  interface  became  the
consensus choice for an industry standard, and the number of
vendors marketing, selling and supporting UNIX systems grew,
Berkeley  has been able to start to return to its historical
orientation of doing leading-edge research instead of custo-
mer support.

3. Berkeley UNIX Tomorrow

     For UNIX to become the system of  choice  for  a  large
segment  of the industry, potential customers must have con-
fidence that the product is supported, that future  versions
will  continue to be developed and enhanced, and that future
versions will be upwardly compatible with all past  applica-
tions.  In  addition,  vendors  desiring  to  maximize their
return on investment require that the source code for  their
systems  be  proprietary and are unwilling to make it avail-
able to users under any but the most  onerous  restrictions.
Many  of these changes, while acceptable for most users, are
diametrically opposed to what has  made  UNIX  the  research
platform  of  choice:  low cost, wide availability of source
code, and leading edge technology.

     System development can be likened  to  the  process  of
evolution.  While  gene mutation is critical to the advance-
ment of the species, only one in 100  mutations  produces  a
useful  feature;  the rest result in needless or detrimental
changes. The mere existence of an environment  for  mutation
is  not enough -- some organization must bear responsibility
for brutally pruning the weak, outdated and  useless  ideas.
UNIX  was  fortunate  in  this  sense. Unlike other projects
beset by competing groups jealously guarding their work from
one another, UNIX thrived in an open and cooperative commun-
ity willing to channel its ideas through a central clearing-
house (first Bell Laboratories and later the CSRG), in spite
of the clearinghouse's reputation  for  selective  technical

     Here one must distinguish between the selection process
provided  by research and commercial organizations. Research
organizations can base pruning  decisions  strictly  on  the
coherence of the system and the technical merit of the idea.
They need not concern  themselves  with  how  changes  might
affect  past  variants  of  the system. Commercial organiza-
tions, though, must ensure that changes will not affect pro-
grams  built  to  an obsolete interface. For example, paging
might be a great  idea,  but  it  will  cause  problems  for
software  that  depends on the execution predictability of a

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swap-based  system,  making  it  impossible  for  paging  to
replace  swapping.  As  a result, both schemes must be main-
tained, dramatically increasing the complexity of  the  sys-
tem.  As  the  system becomes more complex, its evolutionary
paths will become increasingly restricted.

     Here the role of a dynamic  research  version  of  UNIX
becomes  clear.  While  it  is only directly used by a small
group of people,  it  provides  an  important  role  as  the
feedstock for the commercial versions of UNIX. Over the long
term, it is reasonable to expect that the most useful  func-
tionality  of  the research systems will be grafted into the
commercial versions. Examples of ideas that began  with  BSD
and  moved into commercial systems include the fast filesys-
tem, TCP/IP networking, and nearly half of the commands  and

     The CSRG spends a significant amount of time collecting
prototypes  of  projects  throughout  the research world and
molding them together into a  coherent  and  usable  system.
Many  of  the ideas do not work out and are dropped in later
releases. The ability to experiment without concern for past
applications  is  critical.  The resulting system is a third
the size and a fraction of the  complexity  of  its  roughly
equivalently  functioned  commercial brethren. This lean and
mean approach allows  the  system  to  evolve  rapidly  (the
nightmare  of  every commercial user, but the dream of every
researcher). A recent example of this type  of  experimenta-
tion  is the prototyping of various proposed POSIX utilities
and interfaces by the CSRG. When drafts of the standard were
implemented,   basic   flaws  in  the  specification  became
apparent. These flaws and suggested solutions were presented
to  the  standards  committees,  resulting in changes to the
standard ensuring that the ratified standard could be  effi-
ciently and correctly implemented. The research system users
also benefit from having a reference implementation  of  the
standard almost from the day that it is finalized.

     Another major influence on  the  UNIX  systems  of  the
future  will  be  the NET/2 release. At least three separate
groups (two in the U.S. and one in Europe)  have  added  the
necessary  source  code  to  the  NET/2 release to make it a
fully functional UNIX system. As the NET/2 release  was  not
proprietary  to  any  person  or organization other than the
University of California and may  be  freely  redistributed,
the  cost  of a UNIX system with source code will be less in
the future than in the current UNIX market by two orders  of
magnitude.  The  UNIX  single-server release by the Carnegie
Mellon University MACH group will also use the NET/2 release
as  a  starting point, making their release freely redistri-
butable without a UNIX source license. The advent of cheaply
available  sources  will make it far easier than ever before
for research  groups  and  users  to  develop  and  exchange

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     The role of designing and implementing  a  leading-edge
research  version  of  UNIX is one that Berkeley is uniquely
equipped to fill. Future Berkeley releases will be oriented,
as  they were in the early days of Berkeley UNIX, toward the
development and integration of a few well-chosen  pieces  of
new research into a leading-edge system.

4. References:

     Joy, W., E. Cooper, R. Fabry, S. Leffler, M.  McKusick,
     D.   Mosher,  ``4.2BSD  System  Manual,''  4.2BSD  UNIX
     Programmer's Manual, Vol 2c, Document #68 August 1983.

     Leffler, S., M.K. McKusick, M. Karels, ``Measuring  and
     Improving  the  Performance of 4.2BSD,'' Usenix Confer-
     ence Proceedings, pp. 237-252, June, 1984.

     McKusick, M.K., M. Karels,  S.  Leffler,  ``Performance
     Improvements  and  Functional Enhancements in 4.3BSD,''
     Usenix Conference Proceedings, pp. 519-531, June, 1985.

     M. McKusick, M. Karels, ``Directions of UNIX at  Berke-
     ley'',  Digest of Papers of the Thirty-second IEEE Com-
     puter Society International  Conference,  Compcon,  San
     Francisco, pp. 196-199, February 23-27, 1987.

     M.  McKusick,  M.  Karels,  K.  Bostic,  ``The  Release
     Engineering of 4.3BSD'', Proceedings of the New Orleans
     Usenix Workshop on  Software  Management,  pp.  95-100,
     April 1989.

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