The Unix Operating System
(from Operating System Concepts, Peterson/Silberschatz)

The first version of Unix was developed in 1969 by Ken Thompson
of the Research Group at Bell Laboratories to use an otherwise
idle PDP-7.

He was soon joined by Dennis Ritchie. Thompson, Ritchie, and
others in the Research Group produced the early versions of
Unix.

Ritchie had previously worked on the Multics project, and
Multics was a strong influence on the newer operating system.
Even the name Unix is merely a pun on Multics. The basic
organization of the file system, the idea of the command
interpreter (the shell) as a user process, the use of a separate
process for each command, the original line-editing characters
(# to erase the last character and @ to erase the entire line),
and numerous other features came directly from Multics. Ideas
from various other operating systems, such as MIT'S CTSS and the
DS-940 system, were also used.

Ritchie and Thompson worked quietly on Unix for many years.
Their work on the first version allowed them to move it to a
PDP-11/20, for a second version. A third version resulted from
rewriting most of the operating system in the systems
programming language C, instead of the previously used assembly
language. C was developed at Bell Labs to support Unix. Unix was
also moved to larger PDP-11 models, such as the 11/45 and 11/70.
Multiprogramming and other enhancements were added when it was
rewritten in C and moved to systems (like the 11/45) with
hardware support for multiprogramming.

As Unix developed, it became widely used within Bell Labs and
gradually spread to a few universities. The first version widely
available outside Bell Labs was Version 6, in 1976. (The version
number for early Unix systems corresponds to the edition number
of the Unix Programmer's Manual that was current when the
distribution was made; the code and the manuals were revised
independently.) In 1978, Version 7 was distributed. This Unix
system ran on the PDP-11/70 and the Interdata 8/32, and is the
ancestor of most modern Unix systems. In particular, it was soon
ported to other PDP-11 models and to the VAX computer line. The
version available on the VAX was known as 32V.

After the distribution of Version 7 in 1978, the Unix Support
Group (USG) assumed administrative control and responsibility
from the Research group for distributions of Unix within AT&T,
the parent organization for Bell Labs. Unix was becoming a
product, not simply a research tool. The Research group has
continued with their own version of Unix to support their own
internal computing, however. The system currently (1985) in
development by the Research group at Bell Labs is Version 8,
which is available only within Bell Labs.

USG mainly provided support for Unix within AT&T. The first
external distribution from USG was System III, in 1982. System
III incorporated features of Version 7, 32V, and also of several
Unix systems developed by groups other than Research. Features
of UNIX/RT, a real-time Unix system, as well as numerous
portions of the Programmer's Work Bench (PWB) were included in
System III.

USG released System V in 1983; it is largely derived from System
III. The divestiture of the various Bell operating companies
from AT&T has left AT&T in a position to aggressively market
System V. USG has been restructured as the Unix System
Development Laboratory (USDL), whose current distribution,
released in 1984, is Unix System V Release 2 (V.2).

The small size, modularity, and clean design of early Unix
systems led to Unix-based work at numerous other computer
science organizations such as Rand, BBN, the University of
Illinois, Harvard, Purdue, and even DEC. The most influential of
the non-Bell Labs and non-AT&T Unix development groups, however,
has been the University of California at Berkeley.

The first Berkeley VAX Unix work was the addition in 1978 of
virtual memory, demand paging, and page replacement to 32V by
Bill Joy and Ozalp Babaoglu to produce 3BSD. The large virtual
memory space of 3BSD allowed the development of very large
programs, such as Berkeley's own Franz Lisp. The memory
management work convinced the Defense Advanced Research Projects
Agency (DARPA) to fund Berkeley for the development of a
standard Unix system for government use (4BSD).

The 4BSD work for DARPA was guided by a steering committee which
included many notable people from the Unix and networking
communities. One of the goals of this project was to provide
support for the DARPA Internet networking protocols (TCP/IP).
This support was provided in a general manner. It is possible in
4.2BSD to uniformly communicate among diverse network
facilities, including local area networks (such as Ethernets and
token rings) and long-haul computer networks (such as DARPA'S
Arpanet).

In addition, Berkeley adapted many features from contemporary
operating systems to improve the design and implementation of
Unix.