Present day commercial Unix versions are well behind the research community. As far back as 1982 the single machine focus of Unix development became an issue in the research community. Accordingly a number of people at Bell Labs including Dennis Ritchie and Rob Pike, both of whom had contributed to the origination of Unix, decided to try to design a truly network based machine operating system.
Plan 9, named after the movie Plan 9 from Outer Space (itself full of bad puns and a defining moment in the history of "B" movies) rethought core Unix ideas about how to implement system resource allocations in the context of a large network rather than a single computer. Thus the original Unix focus on using one machine as a communication nexus among many users was extended in Plan 9 to multiple networked machines - all with multiple users.
Here's a bit from a paper by Rob Pike and six of his colleagues explaining part of the impetus behind it:
Plan 9 began in the late 1980's as an attempt to have it both ways: to build a system that was centrally administered and cost-effective using cheap modern microcomputers as its computing elements. The idea was to build a time-sharing system out of workstations, but in a novel way. Different computers would handle different tasks: small, cheap machines in people's offices would serve as terminals providing access to large, central, shared resources such as computing servers and file servers. For the central machines, the coming wave of shared-memory multiprocessors seemed obvious candidates. The philosophy is much like that of the Cambridge Distributed System [NeHe82]. The early catch phrase was to build a UNIX out of a lot of little systems, not a system out of a lot of little UNIXes.
The problems with UNIX were too deep to fix, but some of its ideas could be brought along. The best was its use of the file system to coordinate naming of and access to resources, even those, such as devices, not traditionally treated as files. For Plan 9, we adopted this idea by designing a network-level protocol, called 9P, to enable machines to access files on remote systems. Above this, we built a naming system that lets people and their computing agents build customized views of the resources in the network. This is where Plan 9 first began to look different: a Plan 9 user builds a private computing environment and recreates it wherever desired, rather than doing all computing on a private machine. It soon became clear that this model was richer than we had foreseen, and the ideas of per-process name spaces and file-system-like resources were extended throughout the system - to processes, graphics, even the network itself.
By 1989 the system had become solid enough that some of us began using it as our exclusive computing environment. This meant bringing along many of the services and applications we had used on UNIX. We used this opportunity to revisit many issues, not just kernel-resident ones, that we felt UNIX addressed badly. Plan 9 has new compilers, languages, libraries, window systems, and many new applications. Many of the old tools were dropped, while those brought along have been polished or rewritten.
Why be so all-encompassing? The distinction between operating system, library, and application is important to the operating system researcher but uninteresting to the user. What matters is clean functionality. By building a complete new system, we were able to solve problems where we thought they should be solved. For example, there is no real 'tty driver' in the kernel; that is the job of the window system. In the modern world, multi-vendor and multi-architecture computing are essential, yet the usual compilers and tools assume the program is being built to run locally; we needed to rethink these issues. Most important, though, the test of a system is the computing environment it provides. Producing a more efficient way to run the old UNIX warhorses is empty engineering; we were more interested in whether the new ideas suggested by the architecture of the underlying system encourage a more effective way of working. Thus, although Plan 9 provides an emulation environment for running POSIX commands, it is a backwater of the system. The vast majority of system software is developed in the 'native' Plan 9 environment.
Plan 9 is open source and available from the vita nuova site.
The ideas behind plan 9 represent much of where Unix is going today - with Sun, in particular, developing many of these ideas in Solaris, the technically most advanced Unix variant, by concurrently expanding its OS vision outwards through network manageable resource allocation and inward to multi-core SMP on a chip.
- These excerpts don't (usually) include footnotes and most illustrations have been dropped as simply too hard to insert correctly. (The wordpress html "editor" as used here enables a limited html subset and is implemented to force frustrations like the CPM line delimiters from MS-DOS).
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- When I make changes suggested in the comments, I make those changes only in the original, not in the excerpts reproduced here.