1.1. History of the UNIX System

1.1. History of the UNIX System The UNIX system has been in wide use for over 30 years and has helped to define many areas of computing. Although numerous individuals and organizations have contributed (and still contribute) to the development of the UNIX system, this book primarily concentrates on the BSD thread of development. Bell Laboratories, which invented UNIX The Computer Systems Research Group (CSRG) at the University of California at Berkeley, which gave UNIX virtual memory and the reference implementation of TCP/IP The FreeBSD project, the NetBSD project, and the OpenBSD project, which continue the work started by the CSRG The Darwin operating system at the core of Apple's OS X. Darwin is based on FreeBSD. Origins The first version of the UNIX system was developed at Bell Laboratories in 1969 by Ken Thompson as a private research project to use an otherwise idle PDP-7. Thompson was joined shortly thereafter by Dennis Ritchie, who not only contributed to the design and implementation of the system, but also invented the C programming language. The system was completely rewritten into C, leaving almost no assembly language. The original elegant design of the system [Ritchie, 1978] and developments of the first 15 years [Ritchie, 1984a; Compton, 1985] have made the UNIX system an important and powerful operating system [Ritchie, 1987]. Ritchie, Thompson, and other early UNIX developers at Bell Laboratories had worked previously on the Multics project [Peirce, 1985; Organick, 1975], which had a strong influence on the newer operating system. Even the name UNIX is merely a pun on Multics; in areas where Multics attempted to do many tasks, UNIX tried to do only one task but do it well. The basic organization of the UNIX filesystem, the idea of using a user process for the command interpreter, the general organization of the filesystem interface, and many other system characteristics come directly from Multics. Ideas from various other operating systems, such as the Massachusetts Institute of Technology's (MIT's) CTSS, also have been incorporated. The fork operation to create new processes comes from Berkeley's GENIE (SDS-940, later XDS-940) operating system. Allowing a user to create processes inexpensively led to using one process per command rather than commands being run as procedure calls, as is done in Multics. Research UNIX The first major editions of UNIX were the Research systems from Bell Laboratories. In addition to the earliest versions of the system, these systems include the UNIX Time-Sharing System, Sixth Edition, commonly known as V6, which in 1976 was the first version widely available outside of Bell Laboratories. Systems are identified by the edition numbers of the UNIX Programmer's Manual that were current when the distributions were made. The UNIX system was distinguished from other operating systems in three important ways. It was written in a high-level language. It was distributed in source form. It provided powerful primitives normally found in only those operating systems that ran on much more expensive hardware. Most of the system source code was written in C rather than in assembly language. The prevailing belief at the time was that an operating system had to be written in assembly language to provide reasonable efficiency and to get access to the hardware. The C language itself was at a sufficiently high level to allow it to be compiled easily for a wide range of computer hardware, without its being so complex or restrictive that systems programmers had to revert to assembly language to get reasonable efficiency or functionality. Access to the hardware was provided through assembly-language stubs for the 3 percent of the operating-system functions—such as context switching—that needed them. Although the success of UNIX does not stem solely from its being written in a high-level language, the use of C was a critical first step [Kernighan & Ritchie, 1978; Kernighan & Ritchie, 1989; Ritchie et al., 1978]. Ritchie's C language is descended [Rosler, 1984] from Thompson's B language, which was itself descended from BCPL [Richards & Whitby-Strevens, 1980]. C continues to evolve [Tuthill, 1985; ISO, 1999]. The second important distinction of UNIX was its early release from Bell Laboratories to other research environments in source form. By providing source, the system's founders ensured that other organizations would be able not only to use the system, but also to tinker with its inner workings. The ease with which new ideas could be adopted into the system always has been key to the changes that have been made to it. Whenever a new system that tried to upstage UNIX came along, somebody would dissect the newcomer and clone its central ideas into UNIX. The unique ability to use a small, comprehensible system, written in a high-level language, in an environment swimming in new ideas led to a UNIX system that evolved far beyond its humble beginnings. Though recipients of the source code had to be licensed, campuswide licenses were cheaply available to universities. Thus, many people became versed in the way that UNIX worked, setting the stage for the open-source world that would follow. The third important distinction of UNIX was that it provided individual users with the ability to run multiple processes concurrently and to connect these processes into pipelines of commands. At the time, only operating systems running on large and expensive machines had the ability to run multiple processes, and the number of concurrent processes usually was controlled tightly by a system administrator. Most early UNIX systems ran on the PDP-11, which was inexpensive and powerful for its time. Nonetheless, there was at least one early port of Sixth Edition UNIX to a machine with a different architecture: the Interdata 7/32 [Miller, 1978]. The PDP-11 also had an inconveniently small address space. The introduction of machines with 32-bit address spaces, especially the VAX-11/780, provided an opportunity for UNIX to expand its services to include virtual memory and networking. Earlier experiments by the Research group in providing UNIX-like facilities on different hardware had led to the conclusion that it was as easy to move the entire operating system as it was to duplicate UNIX's services under another operating system. The first UNIX system with portability as a specific goal was UNIX Time-Sharing System, Seventh Edition (V7), which ran on the PDP-11 and the Interdata 8/32 and had a VAX variety called UNIX/32V Time-Sharing, System Version 1.0 (32V). The Research group at Bell Laboratories has also developed UNIX Time-Sharing System, Eighth Edition (V8); UNIX Time-Sharing System, Ninth Edition (V9); and UNIX Time-Sharing System, Tenth Edition (V10). Their 1996 system is Plan 9. AT&T UNIX System III and System V After the distribution of Seventh Edition in 1978, the Research group turned over external distributions to the UNIX Support Group (USG). USG had previously distributed internally such systems as the UNIX Programmer's Work Bench (PWB), and had sometimes distributed them externally as well [Mohr, 1985]. USG's first external distribution after Seventh Edition was UNIX System III (System III) in 1982, which incorporated features of Seventh Edition, of 32V, and also of several UNIX systems developed by groups other than the Research group. Features of UNIX/RT (a real-time UNIX system) were included, as were many features from PWB. USG released UNIX System V (System V) in 1983; that system is largely derived from System III. The court-ordered divestiture of the Bell Operating Companies from AT&T permitted AT&T to market System V aggressively [Bach, 1986; Wilson, 1985]. USG metamorphosed into the UNIX System Development Laboratory (USDL), which released UNIX System V, Release 2 in 1984. System V, Release 2, Version 4 introduced paging [Jung, 1985; Miller, 1984], including copy-on-write and shared memory, to System V. The System V implementation was not based on the Berkeley paging system. USDL was succeeded by AT&T Information Systems (ATTIS), which distributed UNIX System V, Release 3, in 1987. That system included STREAMS, an IPC mechanism adopted from V8 [Presotto & Ritchie, 1985]. ATTIS was succeeded by UNIX System Laboratory (USL), which was sold to Novell in 1993. Novell passed the UNIX trademark to the X/OPEN consortium, giving the latter sole rights to set up certification standards for using the UNIX name on products. Two years later, Novell sold UNIX to The Santa Cruz Operation (SCO). Berkeley Software Distributions The most influential of the non-Bell Laboratories and non-AT&T UNIX development groups was the University of California at Berkeley [DiBona et al., 1999]. Software from Berkeley was released in Berkeley Software Distributions (BSD)—for example, as 4.4BSD. Berkeley was the source of the BSD name, and their distributions were the first distinct identity for the BSD operating system. The first Berkeley VAX UNIX work was the addition to 32V of virtual memory, demand paging, and page replacement in 1979 by William Joy and Ozalp Babaoglu, to produce 3BSD [Babaoglu & Joy, 1981]. The reason for the large virtual-memory space of 3BSD was the development of what at the time were large programs, such as Berkeley's Franz LISP. This memory-management work convinced the Defense Advanced Research Projects Agency (DARPA) to fund the Berkeley team for the later development of a standard system (4BSD) for DARPA's contractors to use. A goal of the 4BSD project was to provide support for the DARPA Internet networking protocols, TCP/IP [Comer, 2000]. The networking implementation was general enough to communicate among diverse network facilities, ranging from local networks, such as Ethernets and token rings, to long-haul networks, such as DARPA's ARPANET. We refer to all the Berkeley VAX UNIX systems following 3BSD as 4BSD, although there were really several releases: 4.0BSD, 4.1BSD, 4.2BSD, 4.3BSD, 4.3BSD Tahoe, and 4.3BSD Reno. 4BSD was the UNIX operating system of choice for VAXes from the time that the VAX first became available in 1977 until the release of System V in 1983. Most organizations would purchase a 32V license but would order 4BSD from Berkeley. Many installations inside the Bell System ran 4.1BSD (and replaced it with 4.3BSD when the latter became available). A new virtual-memory system was released with 4.4BSD. The VAX was reaching the end of its useful lifetime, so 4.4BSD was not ported to that machine. Instead, 4.4BSD ran on the newer 68000, SPARC, MIPS, and Intel PC architectures. The 4BSD work for DARPA was guided by a steering committee that included many notable people from both commercial and academic institutions. The culmination of the original Berkeley DARPA UNIX project was the release of 4.2BSD in 1983; further research at Berkeley produced 4.3BSD in mid-1986. The next releases included the 4.3BSD Tahoe release of June 1988 and the 4.3BSD Reno release of June 1990. These releases were primarily ports to the Computer Consoles Incorporated hardware platform. Interleaved with these releases were two unencumbered networking releases: the 4.3BSD Netl release of March 1989 and the 4.3BSD Net2 release of June 1991. These releases extracted nonproprietary code from 4.3BSD; they could be redistributed freely in source and binary form to companies that and individuals who were not covered by a UNIX source license. The final CSRG release requiring an AT&T source license was 4.4BSD in June 1993. Following a year of litigation (see Section 1.3), the free-redistributable 4.4BSD-Lite was released in April 1994. The final CSRG release was 4.4BSD-Lite Release 2 in June 1995. UNIX in the World The UNIX system is also a fertile field for academic endeavor. Thompson and Ritchie were given the Association for Computing Machinery Turing award for the design of the system [Ritchie, 1984b]. The UNIX system and related, specially designed teaching systems—such as Tunis [Ewens et al., 1985; Holt, 1983], XINU [Comer, 1984], and MINIX [Tanenbaum, 1987]—are widely used in courses on operating systems. Linus Torvalds reimplemented the UNIX interface in his freely redistributable Linux operating system. The UNIX system is ubiquitous in universities and research facilities throughout the world, and is ever more widely used in industry and commerce.[@more@]

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